Endangered and Threatened Wildlife and Plants; Critical Habitat Designation for Four Vernal Pool Crustaceans and Eleven Vernal Pool Plants in California and Southern Oregon

AGENCY:

Fish and Wildlife Service, Interior.

ACTION:

Proposed rule.

SUMMARY:

We, the Fish and Wildlife Service (Service), propose designation of critical habitat for 4 vernal pool crustaceans and 11 vernal pool plants with a total area being proposed of approximately 672,920 hectares (ha) (1,662,762 acres (ac)). The proposed designation of critical habitat is for Conservancy fairy shrimp (Branchinecta conservatio) 165,820 ha (409,735 ac), longhorn fairy shrimp (Branchinecta longiantenna) 40,605 ha (100,333 ac), vernal pool fairy shrimp (Branchinecta lynchi) 457,556 ha (1,130,605 ac), and vernal pool tadpole shrimp (Lepidurus packardi) 291,370 ha (719,965 ac) (collectively referred to as “vernal pool crustaceans” in the remainder of this document), and Butte County meadowfoam (Limnanthes floccosa ssp. californica) 16,320 ha (40,326 ac), Contra Costa goldfields (Lasthenia conjugens) 14,499 ha (38,297 ac), Hoover's spurge (Chamaesyce hooveri) 81,744 ha (201,987 ac), succulent (or fleshy) owl's-clover (Castilleja campestris ssp. succulenta) 125,217 ha (309,407 ac), Colusa grass (Neostapfia colusana) 132,608 ha (327,670 ac), Greene's tuctoria (Tuctoria greenei) 142,984 ha (353,308 ac), hairy Orcutt grass (Orcuttia pilosa) 65,671 ha (162,272 ac), Sacramento Orcutt grass (Orcuttia viscida) 24,632 ha (60,865 ac), San Joaquin Valley Orcutt grass (Orcuttia inaequalis) 101,059 ha (249,714 ac), slender Orcutt grass (Orcuttia tenuis) 71,035 ha (175,524 ac), and Solano grass (Tuctoria mucronata) 7,345 ha (18,149 ac) (collectively referred to as “vernal pool plants” in the remainder of this document), pursuant to the Endangered Species Act of 1973, as amended (Act). Because many of the units proposed for different species overlap, the total critical habitat area we are proposing is much less than the sum of the areas for each species. The proposed units are in 39 counties in California and one county in southern Oregon.

If this proposed rule is made final, section 7 of the Act would prohibit destruction or adverse modification of critical habitat by any activity funded, authorized, or carried out by any Federal agency. Section 4 of the Act requires us to consider economic and other impacts of specifying any particular area as critical habitat.

We solicit data and comments from the public on all aspects of this proposal, including data on the economic and other impacts of the designation. We may revise or further refine critical habitat boundaries prior to final designation based on habitat and additional plant and animal surveys, public comments on the proposed critical habitat rule, the completion and approval of Habitat Conservation Plans (HCPs), and new scientific and commercial information, and data concerning potential economic impacts from the proposed designation.

DATES:

We will accept comments from all interested parties until November 25, 2002. Public hearing requests must be received by November 8, 2002.

ADDRESSES:

If you wish to comment, you may submit your comments and materials concerning this proposal by any one of several methods.

1. You may mail written comments and information to the Field Supervisor, Sacramento Fish and Wildlife Office, U.S. Fish and Wildlife Service, 2800 Cottage Way, Room W-2605, Sacramento, CA 95825.

2. You may hand deliver written comments to our Sacramento Fish and Wildlife Office at the address given above.

3. You may send comments by electronic mail (e-mail) to fw1_vernalpool@fws.gov. See the Public Comments Solicited section below for file format and other information about electronic filing.

Comments and materials received, as well as supporting documentation used in the preparation of this proposed rule, will be available for public inspection, by appointment, during normal business hours at the above address.

FOR FURTHER INFORMATION CONTACT:

Arnold Roessler or Susan Moore, at the Sacramento Fish and Wildlife Office address above (telephone 916/414-6600; facsimile 916/414-6710). Information regarding this proposal is available in alternate formats upon request.

SUPPLEMENTARY INFORMATION:

Background

The vernal pool crustaceans and plants addressed in this proposed rule live in vernal pools (shallow depressions that hold water seasonally), swales (shallow drainages that carry water seasonally), and ephemeral freshwater habitats. None are known to occur in riverine waters, marine waters, or other permanent bodies of water. The vernal pool habitats of the four vernal pool crustaceans and eleven plants addressed in this proposed rule have a discontinuous distribution west of the Sierra Nevada that extends from southern Oregon through California into northern Baja California, Mexico (Holland and Jain 1978, 1988, Eriksen and Belk 1999).

Vernal pools are a unique kind of wetland ecosystem. Central to their distinctive ecology is the fact that they are vernal or ephemeral, occurring temporarily—typically during the spring—and then disappearing until the next year. They are wet long enough to be different in character and species composition from the surrounding upland habitats, and yet their prolonged annual dry phase prevents the establishment of species typical of more permanent wetlands. In California, where extensive areas of vernal pool habitat developed over long periods of time, unique suites of species specially adapted to the unusual conditions of vernal pools have evolved. Fish and other predators are among the species excluded by vernal pools' annual drying, so vernal pool communities have developed and flourished in the absence of many predators. California vernal pools are also renowned for their showy displays of wildflowers, blooming in concentric rings about the pools in spring. Centres of Plant Diversity, a project of the World Wide Fund for Nature (WWF) and IUCN—The World Conservation Union, has identified the vernal pools of California and Baja California, Mexico, as a center of plant diversity and endemism in North America, and considers them to be severely threatened (WWF and IUCN 2002).

Many areas in California and portions of southern Oregon have the combination of environmental conditions that favors the development of vernal pools (Keeley and Zedler 1998). The climate is of a type classified as Mediterranean, with a wet season when rainfall exceeds evaporation, filling the pools, and a dry season when evaporation is greater, drying the pools. Rainfall is relatively meager even in most wet seasons, so erosion by overflowing waters does not dissect the topographic irregularities that form vernal pool basins. Temperatures during the winter-spring wet season are mild, so plants and animals can grow, mature, and reproduce.

A second major factor in the development of vernal pools is soil. Vernal pools form where there is a soil layer below or at the surface that is impermeable or nearly impermeable to water (Smith and Verrill 1998). Precipitation and surface runoff become trapped or “perched” above this layer. In California, the restrictive soil layers underlying vernal pools are of four main types—hardpans, claypans, volcanic flows, and non-volcanic rock. Volcanic flows include basaltic lavas and cemented mudflows, and are most common along the lower western slope of the Sierra Nevada. Hardpans are formed by leaching, redeposition, and cementing of silica minerals from high in the soil profile to a lower (“B”) horizon (Hobson and Dahlgren 1998, Smith and Verrill 1998). Claypans are formed by another redeposition process—fine clay particles are transported to the B horizon and accumulate there. Claypans may also be augmented by redeposition of saline or alkaline compounds. Hardpans and claypans both develop gradually over thousands of years, and can be a meter (yard) or more thick. Smith and Verrill (1998) list many of the soil series associated with vernal pools in the Central Valley.

A third factor, related to soil and climate, is topography or relief. Vernal pools typically occur in landscapes that, at a broad scale, are shallowly sloping or nearly level, but on a fine scale may be quite bumpy. Complex micro-relief results in shallow, undrained depressions that form vernal pools. Some vernal pool landscapes are dotted with numerous, rounded soil mounds, referred to as mima mounds, after the well-developed mounds of the Mima Prairie in Thurston County, Washington (Scheffer 1947). Scientists still argue about the origins of these mounds, which have been attributed to forces as disparate as gophers acting over millennia (Scheffer 1947, Cox and Gakahu 1983) and the pressures of soil swelling and shrinkage during wetting and drying cycles (Hallsworth et al. 1955, Hobson and Dahlgren 1998)—as well as other hypotheses, many much less plausible. Focusing on the troughs rather than the mounds, Californians long referred to vernal pools as “hog wallows,” but unlike the buffalo wallows of the Great Plains, these wetlands have little to do with hogs or wallowing. From the air, vernal pool landscapes often show characteristic patterning, produced by plant responses to mound and trough micro-relief. This patterning has allowed detailed mapping of vernal pool habitats throughout California's Central Valley and adjacent areas (Holland 1998).

Vernal pools come in a variety of shapes and sizes, from a square meter (yard) to a hectare (2.5 ac) or more. Some larger vernal wetlands, such as the 36 ha (90 ac) Olcott Lake in the Jepson Prairie Preserve in Solano County, are also referred to as vernal lakes or playa pools or lakes. Playa pools with high alkalinity are termed alkali sinks. These larger wetlands contain many of the same animals and plants of smaller vernal pools, including many rare and endangered species.

Since appropriate combinations of climate, soil, and topography often occur over continuous areas rather than in isolated spots, vernal pools in California, particularly in the Central Valley, tend to occur in clusters, called “complexes.” A landscape that supports a vernal pool complex is typically a grassland, with areas of obstructed drainage that form the pools. Vernal pools can also be found in a variety of other habitats, including woodland, desert, and chaparral. The pools may be fed or connected by low drainage pathways called “swales.” Swales are often themselves seasonal wetlands that remain saturated for much of the wet season, but may not be inundated long enough to develop strong vernal pool characteristics. Vernal pool complexes have historically been considered poor farmland, because of their shallow, seasonally saturated or inundated and sometimes alkaline soils, and their root-restricting subsurface layer. For the same reasons, trees are relatively rare in most vernal pool complexes.

California's vernal pools begin to fill with the fall and winter rains. Before ponding occurs, there is a period during which the soil is wetted and the local water table may rise. Some pools have a substantial watershed that contributes to their water inputs; others may fill almost entirely from rain falling directly into the pool (Hanes and Stromberg 1998). Although exceptions are not uncommon, the watershed generally contributes more to the filling of larger or deeper pools, especially playa pools. Even in pools filled primarily by direct precipitation, Hanes and Stromberg (1998) report that subsurface inflows from surrounding soils can help dampen water level fluctuations during late winter and early spring. Vernal pools exhibit four major phases—the wetting phase, when vernal pool soils become saturated; the aquatic phase, when a perched water table develops and the vernal pool contains water; a water-logged drying phase, when the vernal pool begins loses water as a result of evaporation and loss to the surrounding soils but soil moisture remains high; and the dry phase, when the vernal pool and underlying soils are completely dry (Keeley and Zedler 1998). Upland areas associated with vernal pools are also an important source of nutrients to vernal pool organisms (Wetzel 1975). Vernal pool habitats derive most of their nutrients from detritus which is washed into the pool from adjacent uplands, and these nutrients provide the foundation for vernal pool aquatic communities food chain. Detritus is a primary food source for the vernal pool crustaceans addressed in this proposed rule (Eriksen and Belk 1999).

Both the amount and timing of rainfall in California vary greatly from year to year. As a result, pools may fill to different extents at different times. The duration of ponding of vernal pools also varies, and in certain years some pools may not fill at all. Many characteristics of vernal pool plants and animals are adaptations to the highly variable and unpredictable nature of vernal pools (Holland 1976, Holland and Dains 1990, King et al. 1996, Hanes and Stromberg 1998).

California's vernal pools are rich in species composition compared to vernal pools worldwide and contain many species that are endemic to the region (found nowhere else). In addition, while most of California's grasslands are now dominated by non-native grasses and other introduced plants, vernal pools remain a haven for native species. Invasive non-native plants have been introduced into California and have so successfully spread and reproduced in upland habitats that it is not unusual for non-natives to account for a third of the species and more than 90 percent of the biomass in a California grassland. Vernal pools have dramatically resisted this invasion with 75 to 95 percent of plant species found in vernal pools being native; and natives dominate in biomass as well as number (Holland and Jain 1978, Jokerst 1990, Spencer and Rieseberg 1998). Vernal pool communities dominated by natives persist even though they are surrounded by seas of grassland raining the seed of non-native plants. Vernal pool plant communities are able to resist invasion because of the severe ecological constraints on plants living in vernal pool environments.

The animal communities that live in vernal pools also contain diverse groups of highly specialized species. The freshwater crustacean communities of vernal pools are particularly well developed (Simovich 1998). The most visible crustaceans in vernal pools are the large branchiopods (literally, “gill-foots”), about 27 species in California, of which perhaps 10 are endemic (Helm 1998, Belk and Fugate 2000) and 6 are federally listed as threatened or endangered. The large branchiopods are easily visible to the naked eye, ranging up to 5 centimeters (cm) (2 inches (in)) in length, depending on the species. They include the fairy shrimps (Anostraca), tadpole shrimps (Notostraca), and clam shrimps (Conchostraca). Smaller crustaceans that are common in California vernal pools, many large enough to see without magnification, are water fleas (Branchiopoda—Cladocera), copepods (Copepoda), and seed shrimp (Ostracoda).

Amphibians and many insect species also live in vernal pools. The Pacific tree frog (chorus frog) (Hyla (Pseudacris) regilla) and western toad (Bufo boreas) are common and abundant in and around vernal pools. Two rarer amphibians native to vernal pools are the California tiger salamander (Ambystoma californiense) and the western spadefoot toad (Scaphiopus (Spea) hammondii) (Morey 1998). While dispersing bullfrogs (Rana catesbeiana), which are not native to California, are sometimes found in vernal pools, they do not successfully breed there because bullfrog tadpoles require two years to mature and cannot survive the dry season. These voracious introduced predators will sometimes be found resting and feeding in vernal pools close to more permanent water, frequently associated with human modifications of the landscape. Fish likewise do not inhabit vernal pools, except where temporarily introduced by humans (e.g., mosquitofish (Gambusia sp.)) or by flooding of permanent waters.

The insect fauna of vernal pools is numerous, varied and primarily native, including aquatic beetles (Coleoptera—Dytiscidae, Hydrophilidae, Gyrinidae, Halipidae, Hydraenidae), aquatic bugs, including backswimmers (Hemiptera—Notonectidae), water boatmen (Corixidae), and water striders (Gerridae), springtails (Collembola), mayflies (Ephemeroptera), dragonflies and damselflies (Odonata), and various flies with aquatic larvae, including midges (Diptera—Chironomidae), crane flies (Tipulidae) and mosquitoes (Culicidae). Rogers (1998) found that mosquitoes generally made up less than 2 percent of the total macroscopic invertebrate population in natural and two-year old constructed pools—perhaps because many of the other insects listed above are predators. Vernal pool crustaceans are an important food source for a number of aquatic and terrestrial species. Aquatic predators include insects such as backswimmers (Family Notonectidae) (Woodward and Kiesecker 1994), predaceous diving beetles and their larvae (Family Dystictidae), and dragonflies and damselfly larvae (Order Odonate). Vernal pool tadpole shrimp are another significant predator of fairy shrimp.

The plants, invertebrate and vertebrate animals of vernal pools, and vernal pool landscapes in general, are important providers of food and habitat for waterfowl, shorebirds, wading birds, toads, frogs, and salamanders (Proctor et al. 1967, Krapu 1974, Swanson 1974, Morin 1987, Simovich et al. 1991, Silveira 1996). There is evidence that vernal pool crustaceans were used as a food source for Native Americans in California's Central Valley (Silveira 1998). During the spring, waterfowl feed on vernal pool crustaceans and other invertebrates, which are sources of protein and calcium needed for migration and egg-laying (Proctor et al. 1967, Silveira 1998). Vernal pool complexes contribute to continuity of wetland habitats along the Pacific Flyway (a major bird migration route). Many species feed or nest near vernal pools, for example, cliff swallows (Hirundo fulva) glean mud from vernal pool beds for their nests, lesser nighthawks (Chordeiles acutipennis) nest in dry vernal pool beds, burrowing owl (Athene cunicularia) and gopher (Thomomys sp.) burrows are found in mima mounds, and many species graze or hunt along vernal pool shorelines. Before their populations were nearly eliminated by hunting and habitat alteration, elk (Cervus sp.) and pronghorn antelope (Antilocarpa americana) undoubtedly grazed vernal pool landscapes, and have been replaced by cattle. Fishing net weights found near vernal pools suggests that California's first human populations also made use of vernal pool resources, as do hunters today (Silveira 1998).

Classification of Vernal Pools

The variability of vernal pool types has led many researchers to try and classify these ephemeral habitats. (i.e., Holland (1986), Sawyer and Keeler-Wolf (1995), Ferren et al. (1996), Smith and Verrill (1998)). Most of these efforts have focused on classifying vernal pools based on the factors that influence variation in their physical features. Primary physical features that influence vernal pool size, depth, and soil and water chemistry include soil type, geologic formation, and landform. Landforms are physical attributes of the landscape resulting from geomorphological processes such as erosion and deposition, and include features such as alluvial terraces and basins; and volcanic mudflows and lava flows.

The types and kinds of species that are found in vernal pools are largely determined by these physical factors, including pool size, depth, area, and water and soil chemistry (Holland and Griggs 1976, Zedler 1987, Holland and Dains 1990, Eng et al. 1990, Simovich 1998). The physical characteristics of the vernal pool influences the life history characteristics of vernal pool species, such as the speed with which a species can mature and reproduce, the amount of soil moisture required for germination of plant seeds or hatching of invertebrate eggs or cysts, as well as tolerance to turbidity, total dissolved solids, and other aspects of vernal pool water chemistry.

Sawyer and Keeler-Wolf (1995) classified vernal pools according to a number of physical, geographic, and biological characteristics. They identified several general vernal pool types which correspond to the nature of the impermeable layer that underlay the vernal pool and assisted the pool to form. The vernal pools were identified as Northern Hardpan, Northern Claypan, Northern Basalt Flow, Northern Volcanic Mudflow, and Northern Ashflow vernal pools. Northern Hardpan vernal pools are generally formed on alluvial terraces with silicate-cement soil layers. These pool types are generally on acidic soils, and exhibit well developed mima mound topography found on the eastern margins of the Central Valley. Northern Claypan vernal pools are generally formed on impermeable surfaces created by an accumulation of clay particles. These pool types are often found on basin and basin rim landforms and tend to occur in the central portion of the Central Valley and tend to be alkaline. Vernal pools identified as Northern Volcanic Mudflow, Northern Basalt Flow, and Northern Volcanic Ashflow, are generally formed by an impervious bedrock layer of volcanic origin. These pool types are found on the eastern and coastal portions of the Central Valley, and tend to be small and restricted in distribution. Northern Basalt Flow vernal pools occur at greater elevations than other vernal pool types.

Vernal Pool Crustaceans Background

Conservancy fairy shrimp (Branchinecta conservatio), longhorn fairy shrimp (Branchinecta longiantenna), and vernal pool fairy shrimp (Branchinecta lynchi) are members of the aquatic crustacean order Anostraca. Vernal pool tadpole shrimp (Lepidurus packardi) is a member of the aquatic crustacean order Notostraca. Vernal pool fairy shrimp are found in California and southern Oregon while the other three shrimp species are found only in California. These species have all evolved similar adaptations to the unique habitat conditions of their vernal pool habitats. The general appearance and life history characteristics of these four species will be described in combination below.

Longhorn fairy shrimp, vernal pool fairy shrimp, and Conservancy fairy shrimp (fairy shrimp) have delicate elongate bodies, large stalked compound eyes, and 11 pairs of phyllopods, or gill-like structures that also serve as legs. They swim or glide gracefully upside down by means of complex beating movements that pass in a wave-like anterior to posterior direction. Fairy shrimp are filter feeders, and consume algae, bacteria, protozoa, rotifers, and bits of detritus as they move through the water. The second pair of antennae in fairy shrimp adult males are greatly enlarged and specialized for clasping the females during copulation. The females carry eggs in an oval or elongate ventral sac (brood sac). Once fertilized, the eggs are coated with a protective protein layer that allows them to withstand heat, cold, and prolonged dehydration. The fully developed eggs are either dropped to the pool bottom or remain in the brood sac until the female dies and sinks. These dormant eggs are also known as cysts, and they can remain viable in the soil for decades after deposition (Eriksen and Belk, 1999). When the pools refill in the same or subsequent seasons, some, but not all, of the cysts may hatch (Eriksen and Belk, 1999). The cyst bank in the soil may consist of cysts from several years of breeding. The cysts that hatch may do so within days after the vernal pools fill, and rapidly develop into adults within weeks. In pools that persist for several weeks to a few months, fairy shrimp may have multiple hatches during a single season.

Vernal pool tadpole shrimp have dorsal compound eyes, a large shield-like carapace (shell) that covers most of their body and a pair of long cercopods or appendages at the end of the last abdominal segment. They are primarily benthic (living on the bottoms of the pools) animals that swim with their legs down. Vernal pool tadpole shrimp climb or scramble over objects, and plow along bottom sediments as they forage for food. Their diet consists of organic detritus (decaying matter) and living organisms, such as fairy shrimp and other invertebrates (Fryer 1987). The females deposit eggs on vegetation and other objects on the pool bottom. Like fairy shrimp, vernal pool tadpole shrimp pass the summer months as dormant cysts in the soil. Some of the cysts hatch as the vernal pools are filled with rainwater in the next or subsequent seasons, while other cysts may remain dormant in the soil for many years. When winter rains refill inhabited pools, tadpole shrimp reestablish from dormant cysts and may become sexually mature within three to four weeks after hatching (Ahl 1991, Helm 1998). Mature adults may be present in pools until the habitats dry up in the spring (Ahl 1991, Gallagher 1996).

All of the vernal pool crustacean species addressed in this proposed critical habitat designation have evolved unique physical adaptations to survive in vernal pools. The timing and duration of wet and dry phases can vary significantly from year to year, and in some years vernal pools may not inundate at all. In order to take advantage of the short inundation phase, vernal pool crustaceans have evolved short reproduction times and high reproductive rates. Most of the species addressed in this proposed rule hatch within a few days after their habitats fill with water, and can start reproducing within a few weeks (Eng et al. 1990, Helm 1998, Eriksen and Belk 1999). Vernal pool crustaceans can complete their entire life cycle in a single season, and some species may complete several life cycles. Vernal pool crustaceans can also produce thousands viable cysts when environmental conditions are favorable.

To survive the prolonged heat and dessication of the vernal pool dry phase, vernal pool crustaceans have developed a dormant stage. After vernal pool crustacean eggs are fertilized in the female's brood sac, the embryos develop a thick, usually multi-layered shell. When embryonic development reaches a late stage, further maturation stops, metabolism is drastically slowed, and the egg, now referred to as a cyst, enters a dormant state called diapause. The cyst is then either dropped to the pool bottom or remains in the brood sac until the female dies and sinks. Once the cyst is desiccated, it can withstand temperatures near boiling (Carlisle 1968), fire (Wells et al. 1997), freezing, and anoxic conditions without damage to the embryo. The cyst wall cannot be affected by digestive enzymes, and can be transported in the digestive tracts of animals without harm (Horne 1967). Most fairy shrimp cysts can remain viable in the soil for a decade or longer (Belk 1998).

Although the exact signals that cause crustacean cysts to hatch are unknown, factors such as soil moisture, temperature, light, oxygen, and osmotic pressure may trigger the embryo's emergence from the cyst (Brendonck 1996). Because the cyst contains a well developed embryo, the animal can quickly develop into a fully mature adult. This allows vernal pool crustaceans to reproduce before the vernal pool enters the dry phase, sometimes within only a few weeks (Helm 1998, Eriksen and Belk 1999). In some species, cysts may hatch immediately without going through a dormant stage, if they are deposited while the vernal pool still contains water. These cysts are referred to as quiescent, and allow the vernal pool crustacean to produce multiple generations in a single wet season as long as their habitat remains inundated.

Another important adaptation of vernal pool crustaceans to the unpredictable conditions of vernal pools is the fact that not all of the dormant cysts hatch in every season. Simovich and Hathaway (1997) found that only 6 percent of San Diego fairy shrimp cysts hatched after initial hydration, and only 0.18 percent of Riverside fairy shrimp cysts hatched. The cysts that don't hatch remain dormant and viable in the soil. These cysts may hatch in a subsequent year, and form a cyst bank much like the seed bank of annual plants. The cyst bank may be comprised of cysts from several years of breeding, and large cyst banks of viable resting eggs in the soil of vernal pools containing fairy shrimp have been well documented (Belk 1998). Based on a review of other studies (e.g., Belk 1977, Gallagher 1996, Brendonck 1996), Simovich and Hathaway (1997) concluded that species inhabiting more unpredictable environments, such as smaller or shorter lived pools, are more likely to have a smaller percent of their cysts hatch after their vernal pool habitats fill with water. This strategy reduces the probability of complete reproductive failure if a vernal pool dries up prematurely. This kind of “bet-hedging strategy” has been suggested as a mechanism by which rare species may persist in unpredictable environments (Chesson and Warner 1981, Chesson and Huntly 1989, Ellner and Hairston 1994).

Although the vernal pool crustaceans, and particularly the fairy shrimp, addressed in this proposed rule are not often found in the same vernal pool at the same time, when coexistence does occur, it is generally in deeper, longer lived pools (Eng et al. 1990, Thiery 1991, Gallagher 1996, Simovich 1998). In larger pools, closely related species of fairy shrimp may coexist by hatching at different temperatures, and by developing at different rates (Thiery 1991, Hathaway and Simovich 1996). Vernal pool crustacean species may also be able to coexist by utilizing different physical portions of the vernal pool, or by eating different food sources (Daborn 1978, Mura 1991, Hamer and Appleton 1991, Thiery 1991).

The primary historic dispersal mechanisms for the vernal pool crustaceans probably consisted of large scale flooding resulting from winter and spring rains, and dispersal by migratory birds. As a result of widespread flood control and agricultural water diversion projects developed during the twentieth century, large scale flooding is no longer a major form of dispersal for the vernal pool crustaceans. When being dispersed by migratory birds, the eggs of these crustaceans are either ingested (Krapu 1974, Swanson 1974, Driver 1981, Ahl 1991) and/or adhere to the bird's legs and feathers where they are transported to new habitats. Cysts may also be dispersed by a number of other species, such as salamanders, toads, cattle, and humans (Eriksen and Belk 1999).

The vernal pool crustaceans addressed in this proposed rule are generally confined to habitats that are low to moderate in alkalinity and dissolved salts, when compared with other aquatic systems (Ericksen and Belk 1999). Although potentially moderated by soil type, vernal pools are generally unbuffered and exhibit wide fluctuations in pH and dissolved oxygen (Keeley and Zedler 1998). Vernal pool water ion concentrations, such as sodium, potassium, calcium, chlorine, and magnesium, also experience large daily and seasonal variations. These variations are due to the concentration of ions due to evaporation, and the dilution of ions with additional rainfall throughout the wet season (Barclay and Knight 1981). How vernal pool crustacean species adapt to these fluctuations in water chemistry varies. Definitive conclusion on why the species has certain water chemistry habitat preferences is generally unknown due to the anecdotal nature of observations.

Additional information specific to each of the four individual vernal pool crustacean species described in this proposed rule is provided below.

Conservancy Fairy Shrimp

Conservancy fairy shrimp were first described in 1990 by Eng, Belk, and Eriksen. The type specimens were collected in 1982 at Olcott Lake, Solano County, California. Conservancy fairy shrimp are currently known from only eight disjunct areas—Vina plains and vicinity in southern Tehama and northern Butte County; Jepson Prairie in Solano County; Suisun Slough in southern Solano County; Sacramento National Wildlife Refuge in Glenn County; near Caswell Memorial State Park in Stanislaus County; Haystack Mountain Area in eastern Merced County; San Luis National Wildlife Refuge Complex in central Merced County, and the Mutau Flat area in the Los Padres National Forest area of northern Ventura County.

Conservancy fairy shrimp look similar to other fairy shrimp species, but can be distinguished by characteristics of the male second antenna. The second antennae of Conservancy fairy shrimp males have a distal segment which is about 30 percent shorter than the basal segment, and has a tip bent medially about 90 degrees (Eng et al. 1990). The female brood pouch is tapered at each end, typically extends to abdominal segment 8, and has a terminal opening (Eng et al. 1990). Males may be from 14 to 27 millimeters (mm) (0.6 to 1.1 in) in length, and females have been measured between 14.5 and 23 mm (0.6 and 0.9 in) long.

Further discussion on the life history and habitat requirements of Conservancy fairy shrimp can be found in the final rule to list this species (59 FR 48136).

Longhorn Fairy Shrimp

Longhorn fairy shrimp were first collected in 1937, but were not formally described until 1990 by Eng, Belk, and Eriksen. The type specimen was collected from a sandstone outcrop pool on the Souza Ranch in Contra Costa County, California. Longhorn fairy shrimp are extremely rare, and are only known from three widely separated locations; the Altamont Pass area in Contra Costa and Alameda counties; the western and northern boundaries of Soda Lake on the Carrizo Plain in San Luis Obispo County; and Kesterson National Wildlife Refuge in the San Joaquin Valley in Merced County. Vernal pool crustacean surveys conducted by Sugnet (1993) found only 3 occurrences of longhorn fairy shrimp out of 3,092 locations surveyed, and Helm (1998) found occurrences of longhorn fairy shrimp in only 9 of 4,008 wetlands sampled.

Longhorn fairy shrimp are distinguished from other fairy shrimp by the male's very long second antennae, which is about twice as long, relative to its body, as the second antennae of other species of Branchinecta. Longhorn fairy shrimp antennae range from 6.7 to 10.4 mm (0.3 to 0.4 in) in length (Eriksen and Belk 1999). Females can be recognized by their cylindrical brood pouch, which extends to below abdominal segments 6 or 7. Mature males have been measured between 12 and 21 mm (0.5 to 0.8 in) in length, and females range from 13.3 to 19.8 mm (0.5 to 0.8 in) in length (Eng et al. 1990).

Further discussion on the life history and habitat requirements of longhorn fairy shrimp can be found in the final rule to list this species (59 FR 48136).

Vernal Pool Fairy Shrimp

Vernal pool fairy shrimp were first described by Eng et al. in 1990 from a type specimen that was collected in 1982 at Souza Ranch, Contra Costa County, California. The species occurs in disjunct fragmented habitats distributed across the Central Valley of California from Shasta County to Tulare County and the central and southern coast ranges from northern Solano County to Ventura County, California. Additional disjunct populations have been identified in southern California and in Oregon. In Oregon, the species' distribution is limited to the vicinity of an approximately 82.9 square kilometer (sq km) (32 square mile (sq mi)) area known as the Agate Desert in Jackson County, north of Medford. In southern California the distribution is equally limited with populations occurring in three areas in Riverside County.

Vernal pool fairy shrimp are characterized by the presence and size of several bulges on the male's antenna, and by the female's short, pyriform or pear shaped, brood pouch. Vernal pool fairy shrimp vary in size, ranging from 11 to 25 mm (0.4 to 1.0 in) in length (Eng et al. 1990).

Vernal pool fairy shrimp are currently found in 27 counties across the Central Valley and coast ranges of California, inland valleys of southern California, and southern Oregon. Although vernal pool fairy shrimp are distributed more widely than most other fairy shrimp species, they are generally uncommon throughout their range, and rarely abundant where they do occur (Eng et al. 1990, Eriksen and Belk 1999).

Further discussion on the life history and habitat requirements of vernal pool fairy shrimp can be found in the final rule to list this species (59 FR 48136).

Vernal Pool Tadpole Shrimp

Vernal pool tadpole shrimp were initially described by Simon in 1886, and named Lepidurus packardi. After subsequent reclassification by Longhurst (1955), the species was given a subspecies status based primarily on the lack of apparent geographic boundaries between L. apus and L. packardi populations. Lynch (1972) resurrected L. packardi to full species status based on further examination of specimens and this is the currently accepted taxonomic status of vernal pool tadpole shrimp. Vernal pool tadpole shrimp inhabit sites in California's Central Valley and San Francisco Bay area. The geographic range of this species includes disjunct populations found in the Central Valley from Shasta County to northern Tulare County and in the central coast range from Solano County to Alameda County.

Vernal pool tadpole shrimp are distinguished by a large, shield-like carapace, or shell, that covers the anterior half of their body. Vernal pool tadpole shrimp have 30 to 35 pairs of phyllopods, a segmented abdomen, paired cercopods or tail-like appendages, and fused eyes. Vernal pool tadpole shrimp will continue to grow as long as their vernal pool habitats remain inundated, in some cases for six months or longer. They periodically shed their shells, which can often be found along the edges of vernal pools where vernal pool tadpole shrimp occur. Mature vernal pool tadpole shrimp range in size from 15 to 86 mm (0.6 to 3.4 in) in length.

Vernal pool tadpole shrimp have relatively high reproductive rates. Ahl (1991) found that fecundity increases with body size. Large females, greater than 20 mm (0.8 in) carapace length, could deposit as many as 6 clutches, averaging 32 to 61 eggs per clutch, in a single wet season.

Further discussion on the life history and habitat requirements of vernal pool tadpole shrimp can be found in the final rule to list this species (59 FR 48136).

The habitat of the four vernal pool crustaceans is imperiled by a variety of activities, primarily by urban development, water supply and flood control activities, and conversion of land to agricultural use. Habitat loss occurs from direct destruction and modification of pools due to filling, grading, discing, leveling, and other activities, as well as modification of surrounding uplands. Vernal pool crustaceans and their habitat also are threatened by altered flood regimes, degraded water quality, siltation, erosion, grazing, improper burning, military operations, off-road vehicles, pollution, vandalism, road and trail maintenance, and introduction of non-native predators. Further discussion on threats to the vernal pool crustaceans can be found in the final rule to list these species (59 FR 48136).

Vernal Pool Plants Background

The vernal pool plants described in this proposed rule have developed a suite of highly specialized adaptations which allow them to survive in vernal pool habitats. All eleven species are annuals, meaning they germinate, grow, and reproduce within a single year. This allows the vernal pool plants to complete their life cycles during the relatively short inundation and drying periods of their vernal pool habitat.

Another adaptation of vernal pool plants is production of dormant seeds. This adaptation allows vernal pool plants to survive the hot summer months in the soil. The seeds may remain viable in the soil for many years. The number of plants present above ground may fluctuate dramatically from year to year. However, much of the population of these species exists as seeds in the soil. Vernal pool plant seeds generally germinate after winter rains in response to a complex set of environmental cues that are not well understood, but that generally include temperature and soil moisture. Specific germination cues differ greatly among species and are discussed in more detail in the individual species descriptions below. Not all of the dormant seeds will germinate in any given year. This strategy reduces the probability of local extirpation if environmental conditions change, for example if a vernal pool dries up prematurely. This kind of “bet-hedging strategy” has been suggested as a mechanism by which rare species may persist in unpredictable environments (Chesson and Warner 1981, Chesson and Huntly 1989, Ellner and Hairston 1994).

Tolerance to inundation differs greatly among species (Zedler 1987). The zonation of vernal pool plants which forms the characteristic rings of flowers around vernal pools is a result of this differential tolerance to inundation. Species that are the least tolerant to inundation grow along the margins of the pool, while those that can tolerate extended periods of inundation grow in the center of the pools.

Information on the appearance and life history of each of the eleven individual vernal pool plant species described in this proposed rule is provided below.

Butte County Meadowfoam

Butte County meadowfoam (Limnanthes floccosa ssp. californica) was first collected in 1917 at a site 16 kilometers (km) (10 mi)) north of Chico (Service 1991b), although it was recognized as a separate subspecies at that time. Kalin-Arroyo (1973) determined that Butte County meadowfoam was a distinct taxon and gave it the scientific name Limnanthes floccosa ssp. californica. The type locality is in Butte County between Chico and Oroville, near the intersection of state Highway 99 and Shippee Road (Kalin-Arroyo 1973).

Butte County meadowfoam is a small annual of the meadowfoam or false mermaid family (Limnanthaceae). It has erect stems less than 25 cm (9.8 in) tall. The stem and leaves are densely pubescent (covered with short hairs). The alternate leaves are pinnately compound (divided into distinct segments which are arranged featherlike on either side of a rachis), up to 8 cm (3.1 in) long, and consist of five to eleven leaflets on a long petiole. A single flower arises in the axil (angle between the base of a leaf and the stem) of each upper leaf. The flowers are white with yellow veins, cup or bowl-shaped, and consist of five petals, five sepals, five pistils (female reproductive structures of a flower), and ten stamens (male reproductive structures of a flower) on a long flower stalk (Kalin-Arroyo 1973, McNeill and Brown 1979, Ornduff 1993b).

Butte County meadowfoam seedlings can tolerate short periods of submergence (Jokerst 1989, Dole and Sun 1992). The seedlings develop into rosettes (clusters of leaves near the ground), which do not begin producing flowering stems immediately (McNeill and Brown 1979, Ritland and Jain 1984). Butte County meadowfoam typically begins flowering in February, reaches peak flowering in March, and may continue into April if conditions are suitable. Nutlets are produced in March and April, and the plants die back by early May (Jokerst 1989, Dole and Sun 1992).

Butte County meadowfoam is predominantly self fertilized (Dole and Sun 1992). Nutlets of Butte County meadowfoam apparently are dispersed by water; they can remain afloat for up to 3 days (Hauptli et al. 1978). Limnanthes taxa that grow in wet sites have larger tubercles than those adapted to dry sites. Hauptli et al. (1978) speculated that the tuberculate surface of such nutlets may aid in flotation by trapping air. However, most meadowfoam nutlets are dispersed only short distances. Thus, Butte County meadowfoam nutlets would not be expected to disperse beyond their pool or swale of origin. Birds and livestock are potential sources of long-distance seed dispersal, but specific instances of dispersal have not been documented (Jain 1978).

Butte County meadowfoam has always been confined to the Butte County (Keeler-Wolf et al. 1998). In her original description, Kalin-Arroyo (1973) mentioned six collections, including the type locality. Five of those ranged from the original collection site southeast to Oroville, and the sixth was from Table Mountain north of Oroville. However, Jokerst (1983) did not find Butte County meadowfoam on Table Mountain and later suggested that the specimen had been misidentified (Service 1992a).

All 13 of the occurrences described by the CNDDB (2001) had been reported by 1988 (Kalin-Arroyo 1973, McNeill and Brown 1979, Dole 1988, Jokerst 1989). Five were in northern and northeastern Chico near the municipal airport, four (including the type locality) were from the area around Shippee (northwest of Oroville), and three from southeastern Chico. The other occurrence, northeast of the town of Nord, contained only one plant that was of questionable identity (CNDDB 2001). However, the area indicated would be in the same vicinity as the 1917 collection.

Jokerst (1989) identified “north” and “south” races of Butte County meadowfoam in the Chico “sphere of influence” based on morphology. Later, in studies of enzyme systems, Dole and Sun (1992) confirmed that these races differed genetically. They also identified genetically distinct races that they called “northeast” and “southwest,” with the latter referring to the type locality. They found that 96 percent of genetic diversity in Butte County meadowfoam existed among populations and that little variability was evident within populations. Dole and Sun (1992) used mathematical formulas to estimate an average generation time of 2 years for Butte County meadowfoam and to predict that a seed would be transferred between populations only once every 100 to 200 years. Although considerable morphological variability has been observed within populations, it apparently is attributable to differences in environmental response by plants of the same genetic makeup (Jain 1976, Jokerst 1989).

Two occurrences of Butte County meadowfoam have been extirpated, one each in northern and southeastern Chico (Jokerst 1989, Dole and Sun 1992, Service 1992a, CNDDB 2001). Some of the other 11 occurrences have been reduced in extent (CNDDB 2001). The most recent reports are from 1992 and additional losses could have occurred since then.

Sawyer and Keeler-Wolf (1995) mentioned Butte County meadowfoam as only associated with Northern Basalt Flow vernal pools; however, this pool type was likely based on the erroneous Table Mountain occurrence. Butte County meadowfoam occurs primarily in vernal swales and to a lesser extent on the margins of vernal pools (Kalin-Arroyo 1973, Dole 1988, Jokerst 1989, BioSystems Analysis, Inc. 1993, CNDDB 2001). Swales vary in width from narrow channels to broad, pool-like areas (LSA Associates, Inc. 1994). They may connect in branching, tree-like patterns or in net-like patterns around low mounds. Occupied swales are inundated periodically by water from the surrounding uplands, causing the soil to become saturated. However, Butte County meadowfoam does not persist in pools or swales that are inundated for prolonged periods or remain wet during the summer months, nor in drainages where water flows swiftly (Jokerst 1989, Kelley and Associates Environmental Sciences 1993). BioSystems Analysis Inc. (1993) only found it in the wettest swales in 1992 during the drought. Occupied swales are less than 10 cm (3.9 in) deep (LSA Associates, Inc. 1994) and pools are typically less than 30 m (100 ft) long (Jokerst 1989). In both swales and pools, Butte County meadowfoam may grow along the edges or in the bottom (Kalin-Arroyo 1973, Jokerst 1989). In a study of the Shippee area population (BioSystems Analysis, Inc. 1993) Butte County meadowfoam was found growing more often on pool margins than in the bottom of pools but the pattern was reversed in swales, with the plants more often growing in the center. It typically occurs in long, narrow bands in connected swales or on pool margins but can be found in irregular clusters in isolated drainages (Crompton 1993). Butte County meadowfoam has been found occasionally in disturbed areas such as drainage ditches, firebreaks, and graded sites (McNeill and Brown 1979, Jokerst 1989, Kelley and Associates Environmental Sciences 1992, BioSystems Analysis, Inc. 1993, Kelley and Associates Environmental Sciences 1993).

Further discussion on Butte County meadowfoam's life history and habitat characteristics can be found in the final rule to list the species (62 FR 54807).

Contra Costa Goldfields

Greene (1888) first described Contra Costa goldfields, as Lasthenia conjugens, from specimens collected near Antioch, California. Hall (1914) later lumped Contra Costa goldfields in with the common species Fremont's goldfields, which at that time was called Baeria fremontii. Ferris (1958) proposed the name Baeria fremontii var. conjugens to recognize the distinctiveness of L. conjugens. Finally, Ornduff (1966) restored Greene's original name and rank, returning this species to the genus Lasthenia.

Contra Costa goldfields is a showy spring annual in the aster family (Asteraceae). Its stems are 10 to 30 cm (4 to 12 in) tall, somewhat fleshy, and usually are branched. The leaves are opposite and narrow; the lower leaves are entire, but stem leaves have one or two pairs of narrow lobes. The daisy-like flower heads are solitary (Greene 1888, Ornduff 1993a).

As a vernal pool annual, seeds of Contra Costa goldfields would be expected to germinate in response to autumn rains, with the plants maturing in a single growing season, setting seed, and dying back during the summer. However, detailed research on the life cycle has not been conducted. Contra Costa goldfields flower from March through June (Ornduff 1966, Ornduff 1979, Skinner and Pavlik 1994). The flowers are self-incompatible (Crawford and Ornduff 1989). Insect visitors to flowers of Lasthenia belong to five orders—Coleoptera, Diptera, Hemiptera (true bugs), Hymenoptera (ants, bees and wasps), and Lepidoptera (butterflies and moths) (Thorp and Leong 1998). Most of these insects are generalist pollinators. Some Lasthenia are pollinated by specialist solitary bees (family Andrenidae); including two bee species in the subgenus Diandrena (Andrena submoesta and A. puthua) and five or six species in the subgenus Hesperandrena (Andrena baeriae, A. duboisi, A. lativentris, and two or three undescribed species) (Thorp and Leong 1998). The extent to which pollination of Contra Costa goldfields depends on host-specific bees or more generalist pollinators is currently unknown.

Seed dispersal mechanisms in Contra Costa goldfields are unknown. However, the lack of a pappus or even hairs on the achenes makes wind dispersal unlikely (Ornduff 1976). Seed longevity, survival rates, fecundity, and other demographic parameters have not been investigated. However, as with other vernal pool annuals, population sizes have been observed to vary by up to four orders of magnitude from year to year (CNDDB 2001).

By far the greatest concentration of this species is in Solano County where Contra Costa goldfields are found in the area east and south of the City of Fairfield. Other areas that support populations of this species include the central coast between Monterey and Alameda counties, including Fort Ord in Monterey County, San Francisco Bay National Wildlife Refuge, and near Fremont, in Alameda County. The Santa Barbara County occurrence has probably been lost due to habitat alteration (CNDDB 2001). Contra Costa goldfields also occurs near Manchester in Mendocino County, and at Suscol Ridge in Napa County. Another Napa County site, Milliken Canyon, contained only a single plant in 1987 and may or may not be still in existence (CNDDB 2001). The other existing occurrence is near Rodeo in Contra Costa County (CNDDB 2001).

Further discussion on Contra Costa goldfields' life history and habitat characteristics can be found in the final rule to list the species (62 FR 33037).

Hoover's spurge

Hoover's spurge (Chamaesyce hooveri) was originally named Euphorbia hooveri based on a specimen collected by Hoover in Yettem, Tulare County (Wheeler 1940). Koutnik (1985) placed the species in the genus Chamaesyce as Chamaesyce hooveri.

Hoover's spurge is an annual herb of the spurge family (Euphorbiaceae). Hoover's spurge trails along the ground, forming gray-green mats 5 to 100 cm (2.0 to 39.4 in) in diameter (Broyles 1987, Stone et al. 1988). The stems are hairless and contain milky sap. The tiny (2 to 5 mm (0.08 to 0.20 in)) leaves are opposite, rounded to kidney-shaped, with an asymmetric base and a toothed margin. In the genus Chamaesyce, the structures that appear to be flowers actually are groups of flowers; each group is referred to as a cyathium (Koutnik 1993).

Few details of the life history of Hoover's spurge are known. Seeds of Hoover's spurge germinate after water evaporates from the pools; the plants cannot grow in standing water (Alexander and Schlising 1997). The indeterminate growth pattern allows the plants to continue growing as long as sufficient moisture is available. The proportion of seedlings surviving to reproduction has not been documented; in years of below normal rainfall, seedling survival was characterized as “low” (Stone et al. 1988). The phenology (timing of various stages in the life cycle of a plant) varies among years and among sites, even for those populations in close proximity (Stone et al. 1988). Populations in Merced and Tulare counties typically flower from late May through July, whereas those in Stanislaus County and the Sacramento Valley flower from mid-June into October (Alexander and Schlising 1997, CNDDB 2001, J. Silveira USFWS pers. comm.). Seed set apparently begins soon after flowering. Seed production has not been quantified or studied in relation to environmental factors, but Stone et al. (1988) reported that large plants may produce several hundred seeds. Horned larks (Eremophila alpestris) have been observed eating seeds of Hoover's spurge and thus may assist in seed dispersal (Alexander and Schlising 1997).

Demographic data suggest that seeds of Hoover's spurge can remain dormant until the appropriate temperature and moisture conditions occur. This is evident from the fact that plants can be absent from a given pool for up to four years and then reappear in substantial numbers. Although certain years appear to be more favorable for Hoover's spurge than others, population trends vary from pool to pool, even within the same year in the same area. Moreover, a particular year may be favorable for Hoover's spurge at one site and unfavorable at another. For example, Hoover's spurge was extremely abundant on the Vina Plains Preserve in 1995, but reached a 7-year low at Sacramento National Wildlife Refuge that year. Five occurrences of Hoover's spurge have numbered 5,000 or more plants at their maximum size. Four of those five occur on the Vina Plains, and the other occurs in Tulare County (Stone et al. 1988, CNDDB 2001).

Hoover's spurge probably is pollinated by insects. Related species in the spurge family are pollinated by flies (Heywood 1978, Stone et al. 1988). Also, glands on the plant produce nectar (Wheeler 1941), which is attractive to insects. Beetles, flies, bees and wasps, and butterflies and moths (order Lepidoptera) have been observed visiting the flowers of Hoover's spurge and may potentially serve as pollinators (Stone et al. 1988, Alexander and Schlising 1997). Related species in the genus Euphorbia typically are cross-pollinated because the female flowers on each plant mature before the male (Heywood 1978, Stone et al. 1988), which may or may not be the case for Hoover's spurge.

For decades, Hoover's spurge was known from only three localities—near Yettem and Visalia in Tulare County, and near Vina in Tehama County. Collections were made from these three areas in the late 1930's and early 1940's (Wheeler 1941, Munz and Keck 1959, Stone et al. 1988). From 1974 through 1987, 21 additional occurrences of Hoover's spurge were reported. The majority of these (15) were in Tehama County. One to three occurrences were discovered during this period in each of Butte, Merced, Stanislaus, and Tulare counties (Stone et al. 1988, CNDDB 2001).

The CNDDB (2001) now includes 30 occurrences of Hoover's spurge. In addition to those known historically, six occurrences were discovered in 1992 (three each in Glenn and Tulare counties). Of the 30 occurrences, one each in Tehama and Tulare counties are classified as extirpated; two others, in Butte and Tehama counties, are “possibly extirpated” because this species was not observed for two consecutive years (Stone et al. 1988, CNDDB 2001). Of the 26 occurrences presumed to be extant, only 12 have been observed within the past decade (CNDDB 2001).

The main area of concentration for Hoover's spurge is within the northeastern Sacramento Valley. The Vina Plains of Tehama and Butte counties contains 14 (53.8 percent) of the 26 extant occurrences for Hoover's spurge (CNDDB 2001) in an area approximately 91 sq km (35 sq mi) in extent (Stone et al. 1988). One other site in the same region is near Chico in Butte County. Seven of the extant occurrences are in Southern Sierra Foothills Vernal Pool Region, including five in the Visalia-Yettem area of Tulare County and two in the Hickman-La Grange area of Stanislaus County. Three other occurrences are on the Sacramento National Wildlife Refuge in Glenn County, which is in the Solano-Colusa Vernal Pool Region. The one other extant occurrence is on the Bert Crane Ranch in Merced County, which is within the San Joaquin Valley Vernal Pool Region (Keeler-Wolf et al. 1998, CNDDB 2001).

Further discussion on Hoover's spurge's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14351).

Succulent Owl's-Clover

Succulent (or fleshy) owl's-clover was first described by Hoover (1936a) as Orthocarpus campestris var. succulentus. The type specimen had been collected at Ryer, in Merced County. Hoover (1968) subsequently raised succulent owl's-clover to the rank of species and assigned it the name Orthocarpus succulentus. Chuang and Heckard (1991) reconsidered the taxonomy of Orthocarpus and related genera. Based on floral morphology (external structure or form), seed morphology, and chromosome number, they transferred many species into the genus Castilleja. Furthermore, they determined that the appropriate rank for succulent owl's-clover was as a subspecies of Castilleja campestris (field owl's-clover). The scientific name currently assigned to the plant is Castilleja campestris ssp. succulenta (Chuang and Heckard 1991).

Succulent owl's-clover is a hemiparasitic (partly parasitic) annual herb belonging to the snapdragon family (Scrophulariaceae). It has erect or decumbent stems up to 30 cm (11.8 in) long. The stems are usually unbranched and without hairs. The leaves at the base of the stem are small and scalelike, whereas those on the upper stem are lance-shaped, not lobed, thick, fleshy, brittle, and easily broken. The bracts (leaf-like structures in the flowering structure) are green, similar to but shorter than the upper leaves, and longer than the flowers. Overall, the inflorescence (entire flowering structure of a plant) may occupy as much as half of the plant's height (Hoover 1936a, Hoover 1937, Hoover 1968, Chuang and Heckard 1991, Chuang and Heckard 1993).

As with many related species, succulent owl's-clover is a hemiparasite, meaning that it obtains water and nutrients by forming root grafts with other host plants but manufactures its own food through photosynthesis (Chuang and Heckard 1991). Research on hemiparasitism has focused on related species of Castilleja, but not specifically on succulent owl's-clover. Many different plants can serve as hosts for a single species or even a single individual of Castilleja. Seeds do not require the presence of a host to germinate, and form root connections only after reaching the seedling stage. Some seedlings can survive to maturity without attaching to a host's roots, but in general reproduction is enhanced by root connections (Atsatt and Strong 1970).

The conditions necessary for germination of succulent owl's-clover seeds have not been studied, nor has the timing of seed germination been documented. Flowering occurs in April and May (Skinner and Pavlik 1994). Although many related taxa of Castilleja are pollinated by generalist bees (Superfamily Apoidea) (Chuang and Heckard 1991), succulent owl's-clover is thought to be self-pollinating. Among close relatives that do not require insect pollinators, flower structure and timing of stigma receptivity maximize the chances for self-fertilization and seed set. Even so, insects may transfer some pollen among individual plants and species occurring in the same area. Self-pollinating species of Castilleja typically occur as widely scattered individuals, rather than in dense colonies (Atsatt 1970). Succulent owl's-clover follows this pattern in part, often occurring in many pools within a complex but with fewer than 100 plants per pool. However, succulent owl's-clover also may occur in large populations within a single pool (California Natural Diversity Data Base (CNDDB) 2001). Little is known about the demography of succulent owl's-clover, although population size can fluctuate greatly from year to year. In the few populations where population size was reported for more than 1 year, fluctuations up to two orders of magnitude were noted (CNDDB 2001).

Succulent owl's-clover is known from vernal pool habitats along the Southern Sierra Foothills ranging from Madera County to a disjunct occurrence in northern San Joaquin County. The highest density of occurrences of succulent owl's-clover occurs in Merced County, but the species is also known from Fresno, Madera, Stanislaus, and San Joaquin counties.

Further discussion on succulent owl's-clover life history and habitat characteristics can be found in the final rule to list the species (62 FR 14351).

Orcuttieae Tribe

Colusa grass, hairy Orcutt grass, Solano grass, Greene's tuctoria, Sacramento Valley Orcutt grass, San Joaquin Valley Orcutt grass, and slender Orcutt grass belong to the tribe Orcuttieae in the grass family, Poaceae (Reeder 1965). Many life history characteristics are common to all members of the Orcuttieae. All are wind pollinated, but pollen probably is not carried long distances between populations (Griggs 1980, Griggs 1981, Griggs and Jain 1983). Local seed dispersal is by water, which breaks up the inflorescence (Reeder 1965, Crampton 1976, Griggs 1980, Griggs 1981). Long distance dispersal is unlikely (Service 1985c) but seed may have been carried occasionally by waterfowl (family Anatidae), tule elk (Cervus elaphus nannoides), or pronghorn (Antilocapra americana) in historical times (Griggs 1980). The seeds can remain dormant for an undetermined length of time, but at least for 3 or 4 years, and germinate underwater after they have been immersed for prolonged periods (Crampton 1976, Griggs 1980, Keeley 1998a). Unlike typical terrestrial grasses that grow in the uplands surrounding vernal pools, members of the Orcuttieae flower during the summer months (Keeley 1998a).

All members of the Orcuttieae tribe have large soil seed banks that may often be 50 times or more larger in numbers than the above ground population in any given year. In general, years of above average rainfall promote larger populations of Orcuttieae, but population responses vary by pool and by species (Griggs 1980, Griggs and Jain 1983). Population sizes have been observed to vary by one to four orders of magnitude among successive years and to return to previous levels even after 3 to 5 consecutive years when no mature plants were present (Griggs 1980, Griggs and Jain 1983, Holland 1987). Thus, many years of observation are necessary to determine whether a population is stable or declining.

All members of the Orcuttieae are endemic to vernal pools. Although the various species have been found in pools ranging widely in size, the vast majority occur in pools of 0.01 ha (0.03 ac) to 10 ha (24.7 ac) (Stone et al. 1988). Larger pools retain water until May or June, creating optimal conditions for Orcuttieae (Crampton 1959, Crampton 1976, Griggs 1981, Griggs and Jain 1983). Orcuttieae occur in patches within the pools that are essentially devoid of other plant species (Crampton 1959, Crampton 1976). Typically, plants near the center of a pool grow larger and produce more spikelets than those near the margins, but patterns vary depending on individual pool characteristics and seasonal weather conditions (Griggs 1980).

The specific life history requirements and distribution of each of the seven Orcuttieae species are provided below.

Colusa Grass

Colusa grass (Neostapfia colusana) was first described by Davy (1898), and given the Latin name Stapfia colusana. He had collected the type specimen near the town of Princeton in Colusa County. Davy soon realized that the name Stapfia had already been assigned to a genus of green algae and therefore changed the scientific name of Colusa grass to Neostapfia colusana (Davy 1899). Two other taxonomists proposed alternate Latin names for the genus in the same year, but neither is accepted today. No other species of Neostapfia are known (Reeder 1982, Reeder 1993).

Unlike terrestrial grasses, Colusa grass has pith filled stems, lacks distinct leaf sheaths and ligules, and produces exudate (aromatic, sticky fluid discharged from the plant surface). Colusa grass stems and inflorescence (flower cluster) differs from other members of the Orcuttieae. The plant is pale green when young (Davy 1898) but becomes brownish as the exudate darkens (Reeder 1982, Reeder 1993).

Existing populations of Colusa grass are concentrated northeast of the city of Merced in Merced County and east of Hickman in Stanislaus County. Colusa grass also occurs in central Merced County, in southeastern Yolo County, and in central Solano County (Stone et al. 1988, Keeler-Wolf et al. 1998, CNDDB 2001). This species has been extirpated from Colusa County (CNDDB 2001).

In the 50 years after its initial discovery (Davy 1898), Colusa grass was reported from only three sites other than the type locality; these were in Merced and Stanislaus counties. By the mid-1970's Colusa grass had been reported from a total of 11 sites in Colusa, Merced, Solano, and Stanislaus counties (Hoover 1936b, Hoover 1940, Crampton 1959, Medeiros 1976, Reeder 1982). During the 1980's, many new populations of Colusa grass were located during extensive surveys. As of 1989, 40 occurrences were extant and 11 already had been extirpated. Of the 51 occurrences known up to that point, 26 were in Merced County, 22 were in Stanislaus County, 2 were in Solano County, and one was in Colusa County (Stone et al. 1988, CNDDB 2001). Currently, the CNDDB (2001) considers 48 occurrences of Colusa grass to be “presumed extant” and 11 others as known or possibly extirpated.

Further discussion on Colusa grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

Greene's Tuctoria

Greene's tuctoria (Tuctoria greenei) was originally assigned its name by Vasey (1891) as Orcuttia greenei. Greene had collected the type specimen in 1890 “on moist plains of the upper Sacramento, near Chico, California” (Vasey 1891), presumably in Butte County (Hoover 1941, Crampton 1959). Citing differences in lemma morphology, arrangement of the spikelets, and other differences, Reeder (1982) segregated the genus Tuctoria from Orcuttia and created the new scientific name Tuctoria greenei for this species.

Greene's tuctoria is an erect to low growing annual with fragile stems that easily break apart at the nodes, which are often purplish. The leaves are flat and curve outward and the plants are sparsely hairy. The inflorescence is crowded near the tip with the lower spikelets more or less separated. Optimum germination of Greene's tuctoria seed occurs when the seed is exposed to light and anaerobic (lacking oxygen) conditions after stratification (Keeley 1988). Germination occurs several months after initial inundation (Keeley 1998a). Tuctoria seedlings do not develop floating juvenile leaves, as does Orcuttia (Griggs 1980, Keeley 1998a). The adult plants apparently do not tolerate inundation; all five Greene's tuctoria plants in a Glenn County pool died when the pool refilled during late spring rains in 1996 (Silveira in litt. 1997). Greene's tuctoria flowers from May to July (Skinner and Pavlik 1994), with peak flowering in June and July (Griggs 1981, Broyles 1987).

As with other vernal pool annuals, population size in Greene's tuctoria can vary enormously from year to year, and populations that have no visible plants one year can reappear in large numbers in later years. Population fluctuations may be due to annual variations in weather, particularly rainfall, to changes in management, or to a combination of the two. Such fluctuations were observed at scattered sites in Butte and Tehama counties during the 1970's (Griggs 1980, Griggs and Jain 1983) and at Sacramento National Wildlife Refuge, where the population in the single occupied pool ranged from zero to 60 plants between 1994 and 1999 (Silveira in litt. 2000). Fluctuations of as much as three orders of magnitude were documented on the Vina Plains Preserve during the 1980's and 1990's (Alexander and Schlising 1997)

After its discovery in Butte County in 1890, Greene's tuctoria was not seen again for over 40 years. During extensive surveys in the late 1930's, Hoover (1937, 1941) found the species at sites in Fresno, Madera, Merced, San Joaquin, Stanislaus, Tehama, and Tulare counties. In fact, he described it as the most common of all Orcuttia species, with which it was classified at the time. By the end of the 1980's, Greene's tuctoria had been reported from a total of 36 occurrences in the same 8 counties (Stone et al. 1988, CNDDB 2001).

Three additional occurrences of Greene's tuctoria have been discovered during the past decade, bringing the reported total to 39 occurrences (Oswald and Silveira 1995, CNDDB 2001). However, 19 of the historical occurrences apparently have been extirpated. The other 20 occurrences are presumed to be still in existence, although 6 of those have not been verified for more than a decade (Alexander and Schlising 1997, CNDDB 2001).

Sixty percent of the extant occurrences of Greene's tuctoria are in the Vina Plains area of Tehama and Butte counties. Eastern Merced County has about 30 percent of the known occurrences. Other occurrences are located in Glenn (Oswald and Silveira 1995) and Shasta counties (CNDDB 2001). Greene's tuctoria has been extirpated from Fresno, Madera, San Joaquin, Stanislaus, and Tulare counties (Stone et al. 1988, Skinner and Pavlik 1994, CNDDB 2001).

Further discussion on Greene's tuctoria's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

Hairy Orcutt Grass

Hoover (1941) described hairy Orcutt grass as (Orcuttia pilosa) from specimens he collected in Stanislaus County, “12 miles east of Waterford” in 1937. Hairy Orcutt grass grows in tufts consisting of numerous stems. The stems are decumbent (laying on the ground with the tip turned upward) or erect and branch from only the lower nodes. Almost the entire plant is pilose or hairy, giving it a grayish appearance. The spikelets near the tip of the inflorescence are crowded together, whereas those near the base are more widely spaced.

Griggs (1974 cited in Stone et al. 1988) found that stratification followed by temperatures of 15 to 32°C (59 to 90°F) was necessary for seed germination in hairy Orcutt grass. Flowering period for the plant is mid-April through July. Seed production has not been studied extensively in hairy Orcutt grass, but Griggs and Jain (1983) did note that one individual produced more than 10,000 seeds. Although the predominant pollination agent for all Orcutt grasses is wind, native bees (Halictidae) have been observed visiting the inflorescence of hairy Orcutt grass to gather pollen (Griggs 1974 cited in Stone et al. 1988).

Like other vernal pool annuals, the size of hairy Orcutt grass populations fluctuates dramatically from year to year. Population sizes have varied by as much as four orders of magnitude over time (Griggs 1980, Griggs and Jain 1983, Alexander and Schlising 1997). In fact, two populations that had no visible plants for three successive years exceeded 10,000 plants in the fourth year (Griggs 1980, Griggs and Jain 1983).

Hairy Orcutt grass is known from sites in the southern portion of the Sacramento Valley and the southern Sierra foothills (Keeler-Wolf et al. 1998). The species has been found in Tehama, Stanislaus, Madera, and Merced counties (Hoover 1941, Crampton 1959, Reeder 1982, Stone et al. 1988, CNDDB 2001). Hairy Orcutt grass also was collected in Glenn County, in 1937 (CNDDB 2001); the specimen has since been lost but may have been misidentified as California Orcutt grass (Silveira in litt. 2000). During the late 1980's, Stone et al. (1988) determined that 12 historical occurrences had been extirpated but they and others discovered three additional populations in Madera, Stanislaus, and Tehama counties. One other occurrence from Madera County was previously considered to be hairy Orcutt grass and is listed as such in the CNDDB (2001); however, this population since has been identified as San Joaquin Valley Orcutt grass (Stone in litt. 1992).

Within the past decade, hairy Orcutt grass has been discovered in additional areas in Glenn, Madera, and Tehama counties (CNDDB 2001). Hairy Orcutt grass has also been discovered in another pool at the Vina Plains Preserve in Tehama County (Alexander and Schlising 1997). Of the 38 element occurrences listed by the CNDDB (2001), not counting the misidentified population of San Joaquin Valley Orcutt grass, 24 natural occurrences are presumed to be still in existence. Nineteen of those occurrences have been confirmed as existing within the past decade (CNDDB 2001).

Further discussion on hairy Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

Sacramento Orcutt Grass

Hoover (1941) first described Sacramento Orcutt grass (Orcuttia viscida) as Orcuttia californica var. viscida based on the type specimen he collected from “7 miles south of Folsom” in Sacramento County. Reeder (1980) determined that the differences in morphology, seed size, and chromosome number were sufficient grounds to elevate Sacramento Orcutt grass to the species level as Orcuttia viscida.

In basic form, Sacramento Orcutt grass resembles other members of the tribe and genus. Although all members of the Orcuttieae produce exudate, Sacramento Orcutt grass is particularly viscid even when young. The plants are densely tufted, bluish green, and covered with hairs. The stems are erect or spreading, 3 to 10 cm (1 to 4 in) long, and do not branch. The inflorescence occupies the upper one third to one half of the stem and consists of between 5 and 15 spikelets. The spikelets are closely spaced, and although distichous (arranged in two opposing rows) are oriented towards one side of the stem.

Sacramento Orcutt grass flowers in May and June (Griggs 1977, Skinner and Pavlik 1994, Cochrane in litt. 1995a) and sets seed in June and July (Holland 1987). Seeds likely do not disperse far under natural conditions. In a 6-year period, an experimental population spread at most 3 m (10 ft) from the seed source, and 95 percent of plants were within 30 cm (12 in) of the source (Holland in litt. 1986). A demographic study conducted from 1974 to 1978 (Griggs 1980, Griggs and Jain 1983) indicated that Sacramento Orcutt grass produced an average of 500 seeds per plant. At one site in 1978, 88 percent of plants survived to maturity. The size of the seed bank stored in the soil was approximately 44 times as great as the population of growing plants (Griggs 1980, Griggs and Jain 1983). The number of plants varies with rainfall. Large numbers of plants grow only in years when seasonal rainfall exceeds 40 cm (16 in), particularly when heavy rains begin in November and continue through the end of April (Holland 1987). This species is less likely to germinate in years of below normal precipitation than are other members of the tribe (Griggs 1980, Griggs and Jain 1983).

Sacramento Orcutt grass is endemic to the southeastern Sacramento Valley (Keeler-Wolf et al. 1998) and always has been restricted to Sacramento County. The earliest collection was from 1936 near Phoenix Field. Three other occurrences documented in 1941 and 1958 extended the range north to Orangevale and south to near Sloughhouse. Sacramento Orcutt grass was introduced to Phoenix Park, in Sacramento County, in 1978. Three additional natural occurrences were discovered in the late 1980's, including one in extreme southeastern Sacramento County near State Highway 104. Thus, by 1990 this species was known from a total of seven natural occurrences and one introduction (Stone et al. 1988, CNDDB 2001).

Within the past decade, Sacramento Orcutt grass has been discovered at one new site in Sacramento County, within the previously known range. However, one entire occurrence and a portion of another have been extirpated. Thus, eight of the nine occurrences are still in existence. Five occurrences, comprising more than 70 percent of the occupied habitat, are concentrated into a single small area east of Mather Field. Two other occurrences are adjacent to each other-Phoenix Field Ecological Reserve and the introduced population at Phoenix Park. The eighth existing occurrence is near Rancho Seco Lake (Stone et al. 1988, Cochrane in litt. 1995a, CNDDB 2001).

Further discussion on Sacramento Orcutt grass life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

San Joaquin Valley Orcutt Grass

Hoover (1936b) described San Joaquin Valley Orcutt grass (Orcuttia inaequalis) based on a collection from “Montpellier [sic], Stanislaus County.” Hoover (1941) subsequently reduced this taxon to a variety of Orcuttia californica, using the combination Orcuttia californica var. inaequalis. Based on differences in morphology, seed size, and chromosome number, Reeder (1980) restored the taxon to species status.

Mature plants of San Joaquin Valley Orcutt grass grow in tufts of several erect stems. The plant is grayish-green due to the long hairs on the stem and leaves and produces exudate. Orcuttia plants grow underwater for 3 months or more and have evolved specific adaptations for aquatic growth (Keeley 1998a).

The earliest collection of San Joaquin Valley Orcutt grass was made in 1927 from the Fresno-Madera County border near Lanes Bridge (CNDDB 2001). Hoover (1941) mentioned collections from eight sites in Fresno, Madera, Merced, Stanislaus, and Tulare counties. A total of 20 occurrences had been reported by the mid 1970's, all in the same five counties (Crampton 1959, CNDDB 2001), but none remained as of the late 1970's (Griggs 1980, Griggs and Jain 1983). However, since that time San Joaquin Valley Orcutt grass has been discovered in Merced, Madera, and Fresno counties, and recently additional occurrences of San Joaquin Valley Orcutt grass have been found, including sites in Tulare County. Of the 47 occurrences of San Joaquin Valley Orcutt grass reported in CNDDB (2001), 27 are presumed to be still in existence; 17 are certainly extirpated and 3 others are possibly extirpated because the habitat has been modified (CNDDB 2001). However, only 12 of the occurrences presumed still in existence have been revisited within the past decade, so even the most recent information is outdated. This species has been completely extirpated from Stanislaus County but remains in Fresno, Madera, Merced, and Tulare counties (Stone et al. 1988, Skinner and Pavlik 1994, CNDDB 2001).

Further discussion on San Joaquin Valley Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

Slender Orcutt Grass

Slender Orcutt grass (Orcuttia tenuis) was first named by Hitchcock (1934). The type specimen of slender Orcutt grass was collected in Goose Valley, Shasta County, in 1912. Slender Orcutt grass grows as single stems or in small tufts consisting of a few stems. The plants are sparsely hairy and branch only from the upper half of the stem. Although the stems typically are erect, they may become decumbent if many branches form near the stem tip (Reeder 1982). The inflorescence comprises more than half of the plant's height, and the spikelets are more or less evenly spaced throughout the inflorescence.

Optimal germination of slender Orcutt grass is achieved through stratification followed by warm days and mild nights (Griggs 1974 in Stone et al. 1988). Peak flowering of this species typically occurs in May in the Central Valley (Griggs 1981, Reeder 1982) but not until June or July on the Modoc Plateau (Schoolcraft in litt. 2000). Unlike hairy Orcutt grass and Greene's tuctoria, slender Orcutt grass is not likely to die when pools are flooded by late spring or summer rains (Griggs 1980, Griggs and Jain 1983). Conversely, drought has been known to cause 100 percent mortality (Griggs 1980, Griggs and Jain 1983).

Similar to other vernal pool annuals, slender Orcutt grass populations can vary greatly in size from year to year. Fluctuations of up to four orders of magnitude have been documented in Lake and Shasta counties (Griggs 1980, Griggs and Jain 1983). At the Vina Plains Preserve, the single population ranged in size from 1,000 to 147,700 individuals during the five times it was reported over a 13 year period (Stone et al. 1988, Alexander and Schlising 1997). However, slender Orcutt grass populations do not always fluctuate in size. Among five populations of slender Orcutt grass that Griggs tracked from 1973 to 1979, two in the Dales area remained at the same order of magnitude for the entire period. None of the other five species of Orcuttieae included in the study remained stable for the full 7 years (Griggs 1980, Griggs and Jain 1983).

By the mid 1980s, slender Orcutt grass was known from only 18 localities in Lake, Sacramento, Shasta, and Tehama counties (Reeder 1982, Stone et al. 1988). During the late 1980s, Stone et al. (1988) and others (CNDDB 2001) discovered 34 additional occurrences of slender Orcutt grass. Slender Orcutt grass was found primarily in Tehama County, in the vicinity of Dales and on the Vina Plains. The species was also found in the Stillwater and Millville Plains of Shasta County, and at additional sites in Shasta, Siskiyou, Lake, and Sacramento counties (Griggs and Jain 1983, Stone et al. 1988, CNDDB 2001). During the past decade, 27 new occurrences of slender Orcutt grass have been reported. In addition to the counties where it was reported historically, slender Orcutt grass is now known from Lassen and Plumas counties. The extirpated occurrences of slender Orcutt grass were near Reading Airport and Stillwater Plains in Shasta County and additional possibly extirpated occurrences were near Goose Valley and Battle Creek in Tehama and Shasta counties.

Further discussion on slender Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).

Solano Grass

Solano grass (Tuctoria mucronata) was originally described under the name Orcuttia mucronata based on specimens collected “12 miles due south of Dixon, Solano County” (Crampton 1959, p. 108). Reeder (1982) transferred this species to a new genus, Tuctoria, resulting in the currently accepted name Tuctoria mucronata.

Solano grass is grayish-green, pilose, and sticky. The tufted stems are decumbent and do not branch. The long leaves are rolled inward and have pointed tips. The base of the inflorescence is partially hidden by the uppermost leaves. As is characteristic of the genus, the spikelets are arranged in a spiral; the spikelets in the inflorescence of Solano grass are crowded together.

Solano grass typically flowers in June and sets seed during July (Holland 1987). The demography of Solano grass has not been investigated in detail. Annual estimates or counts at Olcott Lake (Holland 1987, CNDDB 2001) indicated that population sizes for this species fluctuate dramatically from year to year, as do other members of the Orcuttieae. Solano grass was not observed at Olcott Lake from 1976 through 1980, then reappeared in 1981 (Holland 1987), indicating that viable seeds can persist in the soil for a minimum of 5 years. Apparently both drought years and years of excessively high rainfall are unfavorable for Solano grass; the largest populations were observed after seasons of 45 to 60 cm (17.7 to 23.6 in) of precipitation (Holland 1987).

Prior to 1985, Solano grass was known only from Olcott Lake in Solano County, which is believed to be the type locality (Crampton 1959, CNDDB 2001). A second occurrence was discovered in 1985 approximately 4 km (2.5 mi) southwest of Olcott Lake (CNDDB 2001). Solano grass is presumed to remain at the type locality, although only four individual plants have been found within the last decade, all in 1993 (CNDDB 2001). The other Solano County site is still in existence. A third occurrence, comprising the largest population known, was discovered in 1993 on a Department of Defense (DOD) communications facility in Yolo County (CNDDB 2001).

Further discussion on Solano grass's life history and habitat characteristics can be found in the Delta Green Ground Beetle and Solano Grass Recovery Plan (Service 1985c).

The vernal pool plants are threatened by habitat loss and degradation due to urbanization, agricultural land conversion, off road vehicle use, flood control projects, highway projects, altered hydrology, landfill projects, and competition from weedy nonnative plants. The habitat of these species has been reduced and fragmented throughout their respective ranges as vernal pools continue to be eliminated. Further discussion on threats to the vernal pool plants can be found in the final rules to list these species (62 FR 34029, 62 FR 14338, 57 FR 24192, 43 FR 44810) and in the criteria section of this proposed rule.

Previous Federal Action (Vernal Pool Crustaceans)

Ms. Roxanne Bittman petitioned us to list Conservancy fairy shrimp, longhorn fairy shrimp, vernal pool fairy shrimp, and California linderiella (Linderiella occidentalis) as endangered species on November 19, 1990. Ms. Dee Warneycia petitioned us to list vernal pool tadpole shrimp as an endangered species on April 28, 1991. On May 8, 1992, we published a proposed rule in the Federal Register (57 FR 19856) to list the four fairy shrimp and vernal pool tadpole shrimp as endangered. On September 19, 1994, we published a final rule in the Federal Register (59 FR 48136) determining endangered status for Conservancy fairy shrimp, longhorn fairy shrimp and vernal pool tadpole shrimp and threatened status for vernal pool fairy shrimp. We withdrew the California linderiella as a species proposed for listing based on additional information received during the public review and comment period indicating that during the review period this species was more abundant than previously known.

On April 17, 1995, the Building Industry Association of Superior California (BIAC) and Marvin L.Oates (Plaintiffs) filed a lawsuit in Federal District Court for the District of Columbia against Bruce Babbit (Secretary, Department of the Interior) et al. (Defendants) and Environmental Defense Center and Butte Environmental Council (Defendent-Intervenors) arguing that the listing of four vernal pool crustaceans (Conservancy fairy shrimp, longhorn fairy shrimp, vernal pool fairy shrimp, and vernal pool tadpole shrimp) violated the Act, the Administrative Procedures Act, the Fifth Amendment, the Tenth Amendment, and the Commerce Clause of the United States Constitution (Building Industry Association of Superior California, et al. v. Babbit et al., CIV 95-0726 PLF). On July 25, 1997, the district court granted the defendant's motion for summary judgement on all aspects except the decision not to designate critical habitat. The plaintiffs later amended their complaint to drop the claim relating to the designation of critical habitat and the district court vacated its ruling regarding this matter. On April 12, 2000, the Butte Environmental Council filed suit, alleging that our failure to establish critical habitat for the four vernal pool crustaceans violated the Endangered Species Act and the Administrative Procedures Act (Butte Environmental Council v. White CIV S-00-797 WES GGH). On February 9, 2001, the U.S. District Court for the Eastern District of California granted the plaintiff's motion for summary judgement and required the defendants, to the maximum extent prudent and determinable, to designate critical habitat for the four vernal pool crustaceans within six months.

On July 23, 2001, the district court approved a settlement agreement between the parties which extended the deadline for designation of critical habitat to August 15, 2002. As a condition of the settlement, we agreed to also designate critical habitat, to the maximum extent prudent and determinable, for the eleven vernal pool plants addressed in this proposed rule by the same date.

Previous Federal Action (Vernal Pool Plants)

Section 12 of the Act directed the Secretary of the Smithsonian Institution to prepare a report on plant species which were or might become endangered or threatened. The resulting report, dated January 9, 1975, reviewed the status of 3,100 vascular plants. The report categorized as endangered six of the eleven vernal pool plants under consideration here, and categorized two others as threatened. The six plants considered endangered were hairy Orcutt grass, Sacramento Orcutt grass, slender Orcutt grass, Colusa grass, San Joaquin Valley Orcutt grass, and succulent owl's clover. The two threatened plants were Contra Costa goldfields and Hoover's spurge. On July 1, 1975, the Director of the Department of the Interior published a notice (40 FR 27823) accepting the Smithsonian Institution's report as a listing petition within the context of section 4(c)(2) of the Act (petition provisions are now found in section 4(b)(3)), and of his intention to review the status of the plants covered by the report. On June 16, 1976, based on both the Smithsonian report and on public comments and data pertaining to it, we published a proposed rule (41 FR 24523) to determine approximately 1,700 vascular plants as endangered pursuant to section 4 of the Act. The 1,700 plants included all eleven vernal pool plants considered here.

We published a final rule to list Solano grass (along with four other plants) as endangered on September 28, 1978 (43 FR 44810). A recovery plan for Solano grass and the delta green ground beetle (Elaphrus viridis) was subsequently approved on September 11, 1985 (Service 1985c). We failed to complete final listing rules for the other ten vernal pool plants within three years of the proposed listing, however, despite amendments to the Act in 1978 requiring us to withdraw proposed rules which were more than two years old (with a one-year grace period). Accordingly, on December 10, 1979, we withdrew the proposal to list the ten remaining vernal pool plants (44 FR 70796).

We established the remaining vernal pool plants as category 1 candidate species in a Notice of Review (NOR) for plants published December 15, 1980 (45 FR 82480). Category 1 candidates were those species for which data in our possession was sufficient to support proposals to list. In a subsequent NOR published November 28, 1983 (48 FR 53640), we downgraded the status of Contra Costa goldfields, slender Orcutt grass and Colusa grass to category 2. Category 2 candidates were defined as species for which data in our possession indicated listing was possibly appropriate, but for which we lacked substantial data on biological vulnerability and threats to support listing proposals. Another NOR on September 27, 1985, left the status of the remaining vernal pool plants unchanged (50 FR 39526).

On February 2, 1988, we received a petition from the California Native Plant Society (CNPS) to emergency list Butte County meadowfoam as endangered. We published a 90-day administrative finding that the requested action might be warranted on December 30, 1988 (53 FR 53030). On February 15, 1991, we published a proposal to list Butte County meadowfoam as an endangered species (56 FR 6345), and on June 8, 1992, we published a final determination that Butte County meadowfoam was endangered (57 FR 24192).

On February 22, 1990, we published a new NOR which re-established Colusa grass and Contra Costa goldfields as category 1 candidate species (55 FR 6184). In 1991 and 1992, we received additional information regarding threats to succulent owl's-clover, and so returned this species to category 1 status on August 5, 1993 (58 FR 41700), in the same notice proposing to list succulent owl's clover and seven other vernal pool plants under the Act.

On August 5, 1993, we published a proposal to list San Joaquin Valley Orcutt grass, hairy Orcutt grass, Sacramento Orcutt grass, and Greene's tuctoria as endangered; and to list succulent owl's-clover, Hoover's spurge, Colusa grass, and slender Orcutt grass as threatened was published on August 5, 1993 (58 FR 41700). This proposal was primarily based on information supplied by reports to the CNDDB, the Status Survey of the Grass Tribe Orcuttieae and Hoover's Spurge in the Central Valley of California (Stone et al. 1988), and observations by numerous botanists. Prior to publishing the final rule on these eight plants, we published another NOR on September 30, 1993 (58 FR 51144), indicating that the current status of the vernal pool plants as category 1 candidates remained unchanged. We subsequently published a proposal to list Contra Costa goldfields as endangered on December 19, 1994 (59 FR 65311). Then on March 26, 1997, we published the final rule (62 FR 14338) for the eight plants proposed for listing in 1993. The final rule listed San Joaquin Valley Orcutt grass as threatened, rather than endangered as had originally been proposed, because we determined the threats to its existence to be smaller and less immediate than had previously been thought. All seven other plants were listed as proposed, resulting in a listing of hairy Orcutt grass, Sacramento Orcutt grass and Greene's tuctoria as endangered; and San Joaquin Valley Orcutt grass, succulent owl's clover, Hoover's spurge, Colusa grass and slender Orcutt grass as threatened. Later that same year (June 18, 1997) we published the final rule to list Contra Costa goldfields, the last of the vernal pool plants considered here, as endangered (62 FR 34029).

We did not identify critical habitat in the final listing rules for any of the vernal pool plants or crustaceans considered here because we determined that the threats of increased vandalism and collection of listed species in the areas thus identified would make it imprudent to do so. Based on the interpretation of section 4 of the Act in a number of judicial decisions issued after the not prudent findings for these species were made, however, we have reconsidered those determinations and now consider the designation of critical habitat for the fifteen vernal pool species to be prudent. We are therefore proposing to designate critical habitat here, for the four vernal pool crustaceans and eleven vernal pool plants covered by the July 23, 2001, court approved settlement agreement in that case.

On August 14, 2002, we filed a motion in Butte Environmental Council seeking to modify the deadline of August 15, 2002, for issuance of final critical habitat determinations. We were unable to meet that deadline, and have asked the court to approve a new deadline of September 30, 2003.

Critical Habitat

Critical habitat is defined in section 3(5)(A) of the Act as: (i) The specific areas within the geographic area occupied by a species at the time it is listed in accordance with the Act, on which are found those physical or biological features (I) essential to the conservation of the species and (II) that may require special management considerations or protection; and (ii) specific areas outside the geographic area occupied by a species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. “Conservation” means the use of all methods and procedures that are necessary to bring an endangered or threatened species to the point at which listing under the Act is no longer necessary.

Critical habitat receives protection under section 7 of the Act through the prohibition against destruction or adverse modification of critical habitat with regard to actions carried out, funded, permitted, or authorized by a Federal agency. Section 7 also requires conferences on Federal actions that are likely to result in the destruction or adverse modification of proposed critical habitat. Aside from the added protection that may be provided under section 7, the Act does not provide other forms of protection to lands designated as critical habitat. Because consultation under section 7 of the Act does not apply to activities on private or other non-Federal lands that do not involve a Federal nexus, critical habitat designation would not afford any additional regulatory protections under the Act.

Critical habitat also provides non-regulatory benefits to the species by informing the public and private sectors of areas that are important for species recovery and where conservation actions would be most effective. Designation of critical habitat can help focus conservation activities for a listed species by identifying areas that contain the physical and biological features essential for the conservation of that species, and can alert the public as well as land-managing agencies to the importance of those areas. Critical habitat also identifies areas that may require special management considerations or protection, and may help provide protection to areas where significant threats to the species have been identified, by helping people avoid causing accidental damage to such areas.

In order to be included in a critical habitat designation, the habitat must first be “essential to the conservation of the species.” Critical habitat designations identify, to the extent known and using the best scientific and commercial data available, habitat areas that provide at least one of the physical or biological features essential to the conservation of the species (primary constituent elements, as defined at 50 CFR 424.12(b)). Section 3(5)(C) of the Act states that not all areas that can be occupied by a species should be designated as critical habitat unless the Secretary determines that all such areas are essential to the conservation of the species. Our regulations (50 CFR 424.12(e)) also state that, “The Secretary shall designate as critical habitat areas outside the geographic area presently occupied by the species only when a designation limited to its present range would be inadequate to ensure the conservation of the species.”

Section 4(b)(2) of the Act requires that we take into consideration the economic impact, and any other relevant impact, of specifying any particular area as critical habitat. We may exclude areas from critical habitat designation when the benefits of exclusion outweigh the benefits of including the areas within critical habitat, provided the exclusion will not result in extinction of the species.

Our Policy on Information Standards Under the Endangered Species Act, published on July 1, 1994 (59 FR 34271), provides criteria, establishes procedures, and provides guidance to ensure that our decisions represent the best scientific and commercial data available. It requires that our biologists, to the extent consistent with the Act and with the use of the best scientific and commercial data available, use primary and original sources of information as the basis for recommendations to designate critical habitat. When determining which areas are critical habitat, a primary source of information should be the listing rule for the species. Additional information may be obtained from a recovery plan, articles in peer-reviewed journals, conservation plans developed by States and surveys and studies, and biological assessments or other unpublished materials.

Section 4 of the Act requires that we designate critical habitat based on what we know at the time of designation. Habitat is often dynamic, and species may move from one area to another over time. Furthermore, we recognize that designation of critical habitat may not include all of the habitat areas that may eventually be determined to be necessary for the recovery of the species. For these reasons, critical habitat designations do not signal that habitat outside the designation is unimportant or may not be required for recovery. Areas outside the critical habitat designation will continue to be subject to conservation actions that may be implemented under section 7(a)(1) of the Act and to the regulatory protections afforded by the section 7(a)(2) jeopardy standard and the section 9 prohibitions, as determined on the basis of the best available information at the time of the action. Federally funded or assisted projects affecting listed species outside their designated critical habitat areas may still result in jeopardy findings. Similarly, critical habitat designations made on the basis of the best available information at the time of designation will not control the direction and substance of future recovery plans, HCPs, or other species conservation planning efforts if new information available to these planning efforts calls for a different outcome.

The action of designating critical habitat does not automatically lead to recovery of a listed species, but it may contribute to species recovery. Critical habitat units are not target preserve areas: designation does not target and establish specific preserves and their boundaries. Critical habitat is designated to make Federal agencies aware that these areas are critical to the species. Although the designation of critical habitat can identify areas where a variety of conservation strategies may be developed to ensure the survival and recovery of target species, the development of these strategies are most appropriately taken through local planning efforts, such as the development of HCPs. The action of designating critical habitat does not result in the creation of management plans, establish numerical population goals, and/or prescribe specific management actions, whether inside or outside of such designated critical habitat. Specific management recommendations for areas designated as critical habitat are most appropriately addressed in recovery, conservation, and management plans, and through consultations and permits under section 7 and section 10 of the Act.

Prudency Redetermination

Section 4(a)(3) of the Act, as amended, and implementing regulations (50 CFR 424.12) require that, to the maximum extent prudent and determinable, we designate critical habitat at the time the species is determined to be endangered or threatened. At the time of the final listing determination (62 FR 34029, 62 FR 14338, 59 FR 48136, 57 FR 24192), we found that designation of critical habitat was not prudent for the vernal pool crustaceans and plants (excluding Solano grass). At the time of final listing of Solano grass (43 FR 44810), we did not make any determination about whether or not designation of critical habitat was prudent. Our regulations (50 CFR 424.12(a)(1)) state that designation of critical habitat is not prudent when one or both of the following situations exist—(1) The species is threatened by taking or other human activity, and identification of critical habitat can be expected to increase the degree of such threat to the species, or (2) such designation of critical habitat would not be beneficial to the species. In our final listing rules for the vernal pool crustaceans and plants (excluding Solano grass), we believed that publication of precise maps and descriptions of critical habitat for the vernal pool crustaceans and plants could make these species more vulnerable to incidents of vandalism or other human activities such as discing, grading, or filling (62 FR 34029, 62 FR 14338, 59 FR 48136, 57 FR 24192). In addition, we determined that publication of precise maps and descriptions of critical habitat for the vernal pool plants would increase the vulnerability of these species to incidents of collection (62 FR 34029, 62 FR 14338, 57 FR 24192). Therefore, we determined that the designation of critical habitat would increase the degree of threat to the vernal pool crustaceans and plants. We also determined that designation of critical habitat was not beneficial for the vernal pool plant species (excluding Solano grass) because many populations of these species were found on private lands (62 FR 34029, 62 FR 14338, 57 FR 24192). For Butte County meadowfoam and Contra Costa goldfields, we believed that Federal involvement in the areas where these plant species occurred could be identified without designation of critical habitat (62 FR 34029, 57 FR 24192). For eight of the vernal pool plant species (succulent owl's-clover, Hoover's spurge, Colusa grass, San Joaquin Valley Orcutt grass, hairy Orcutt grass, slender Orcutt grass, Sacramento Orcutt grass, and Greene's tuctoria), we believed that Federal agencies were aware of the species' presence and were already addressing conservation efforts where the species were found on Federal lands (62 FR 14338).

In 1995, the CDFG received a grant from the U.S. Environmental Protection Agency (EPA) to map vernal pools in particular areas for conservation purposes (Vendlinski 2000). As a result of this effort, the CDFG published a report which delineated 17 vernal pool regions throughout California (Keeler-Wolf et al. 1998). In 1997, Robert Holland's original 1973-1974 map of vernal pools in the Central Valley was updated and the results were documented Holland (1998). In 1998, we published the Recovery Plan for Vernal Pools of Southern California (Service 1998) which outlined recovery strategies for seven vernal pool species (two vernal pool crustaceans and five vernal pool plants) including the San Diego fairy shrimp (Branchinecta sandiegonensis). The release of these data resulted in the widespread distribution of information about vernal pool habitat and its location to the public and to local jurisdictions for planning purposes. Since the release of these data, we have not documented an increase in the threats to the species addressed in this rule through vandalism, collection, habitat destruction, or other means. In contrast, we have witnessed an increase in public interest in the species and their conservation through survey efforts by species experts, scientific research, regional and local planning, and educational outreach. Since listing of the vernal pool crustaceans and plants, several vernal pool conservation planning efforts have been initiated by public agencies and non-government organizations. For example, in 1997 the Framework Agreement for the Interagency Vernal Pool Stewardship Initiative was signed by a number of Federal and State agencies; this agreement encourages coordination of vernal pool conservation efforts on a regional scale between the signatory agencies.

Based on the lack of an increase in vandalism threats, we have reconsidered our evaluation of our original prudency determination. We have determined that the threats to the vernal pool crustaceans and plants and their habitat from the specific instances of habitat destruction we identified in the final listing rules do not outweigh the broader educational, regulatory, and other possible benefits that a designation of critical habitat would provide for these species. The instances of likely vandalism, though real, have been relatively isolated. Consequently, we conclude that designating critical habitat will not increase incidences of habitat vandalism above current levels for these species. In the absence of finding that critical habitat would increase threats to a species, if there are any benefits to critical habitat designation, then a prudent finding is warranted. The potential benefits include: (1) Triggering consultations under section 7 of the Act in new areas where it would not otherwise occur because, for example, it is or has become unoccupied or the occupancy is in question; (2) focusing conservation activities on the most essential areas; (3) providing educational benefits to State or county governments or private entities; and, (4) preventing people from causing inadvertent harm to the species. Therefore, we conclude that the benefits of designating critical habitat on lands essential for the conservation of the vernal pool crustaceans and plants outweigh the risks of increased vandalism resulting from such designation. Critical habitat for the 4 vernal pool crustaceans and 11 vernal pool plants addressed herein is prudent and we are subsequently proposing critical habitat for them in this proposed rule.

All of the proposed critical habitat units contain one or more of the primary constituent elements for the vernal pool crustaceans or plants addressed in this proposed rule. However, as stated earlier, vernal pool crustaceans and plants occur in ephemeral pools that may not be present throughout a given year or from year to year.

In summary, in determining areas that are essential to conserve the species addressed in this proposed rule, we used the best scientific information available to us. The critical habitat areas described below constitute our best assessment of areas needed for the species' conservation.

Methods

In determining critical habitat for vernal pool crustaceans and vernal pool plants we used the best scientific and commercial data available. This included data and information contained in the final rules listing the 15 species addressed herein, research and survey observations published in peer reviewed articles, the Vernal Pools of Southern California Final Recovery Plan (Service 1998), data collected for the development of HCPs, reports submitted by biologists holding section 10(a)(1)(A) recovery permits, data collected for the development of a Wetland Conservation Plan in Oregon, reports and documents that are on file in the Service's field offices, and personal discussions with experts outside of the Service with extensive knowledge of vernal pool species and habitats.

We utilized Geographic Information System (GIS) data derived from a variety of Federal, State, and local agencies, and from private organizations and individuals. To identify where vernal pool species and habitats occur we evaluated GIS data of vernal pool habitats by Holland (1998 and 2002), and species occurrences information from the CNDDB (2001). We presumed occurrences identified in CNDDB to be extant until we received documentation that the occurrences have been extirpated. We also relied on unpublished species occurrence data contained within our files. We produced preliminary maps using GIS information that plotted species occurrences and vernal pool habitats superimposed on SPOT imagery (CNES/SPOT Image Corporation 1993-2000). The use of SPOT imagery allowed us to identify landmarks such as roads, cities, rivers, and urban areas.

Because the minimum mapping unit of the Holland (1998 and 2002) vernal pool habitat data was 16 ha (40 ac) and the resolution of the SPOT imagery did not allow us to identify all vernal pool habitat areas, we then refined unit boundaries based on additional GIS data layers when necessary and available, including soils information from the Soil Survey Geographic (SSURGO) data bases (U.S. Department of Agriculture (USDA) 1998-2001), and the California State Soil Geographic (STATSGO) data bases (USDA 1994). We used geologic information developed by the California Department of Mines and Geology (CDMG) (2000) and Liss (2001). To identify the extent of flat or gently sloping topography where vernal pools are found we evaluated Digital Elevation Models from the U.S. Geologic Survey (2000).

We also used a number of local GIS data sets for specific areas, including information developed through the Riverside Multiple Species HCP and the Vernal Pools of Southern California Final Recovery Plan (Service 1998), habitat mapping for Butte County (EPA 1994), Tehama County (2001), Shasta County (2001) Placer County (Glazner 2001), Solano County (2000), Yolo County (1995), Sacramento County (1999) and San Joaquin County (2000) in California, and by the Rogue Valley Council of Governments in Oregon (Evans 2000). Other smaller scale mapping efforts were reviewed from Solano County Farmlands and Open Space (2000) and East Bay Regional Parks District (2001). The specific layers used and the methodology employed for each unit is described within the unit descriptions. To determine land ownership within each unit we used data from the State of California (Davis et al. 1998) and the U.S. Bureau of Indian Affairs in Sacramento, California (2001).

Primary Constituent Elements

In accordance with section 3(5)(A)(i) of the Act and regulations at 50 CFR 424.12, in determining which areas to propose as critical habitat, we consider those physical and biological features (primary constituent elements) that are essential to the conservation of the species and that may require special management considerations or protection. These features include, but are not limited to—space for individual and population growth, and for normal behavior; food, water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, and dispersal; and habitats that are protected from disturbance or are representative of the historic geographical and ecological distributions of a species.

When considering the designation of critical habitat for vernal pool crustaceans, we focused on the principal biological and physical features that support vernal pool crustacean feeding, growth, breeding, reproduction, and dispersal. Vernal pool crustaceans are found only in ephemeral wetland habitats that contain water during the winter, when temperatures are suitable for cyst hatching and juvenile development. Individuals have never been found in riverine, marine, or other permanent bodies of water.

Generally, we identified two primary constituent elements for all four vernal pool crustacean species addressed in this proposed rule. Each species has primary constituent elements that differ slightly from these general elements discussed in later sections of this rule. We determined that these proposed primary constituent elements of critical habitat provide for the physiological, behavioral, and ecological requirements of the vernal pool crustaceans.

The first primary constituent element provides the aquatic environment required for cyst incubation and hatching, growth and maturation, reproduction, feeding, sheltering, and dispersal, and the appropriate periods of dessication for cyst dormancy and to eliminate predators such as bullfrogs, fish, and other aquatic predators that depend on year round inundation of wetland habitats to survive. We conclude this element is essential to the conservation of vernal pool crustaceans because these species are ecologically dependent on seasonal fluctuations, such as absence or presence of water during specific times of the year, and duration of inundation (59 FR 48136). They cannot persist in perennial wetlands or wetlands that are inundated for the majority of the year, nor can they persist without periodic seasonal inundation.

The second primary constituent element is essential to maintain the aquatic phase of the vernal pool habitat. The entire vernal pool complex, including the pools, swales, and associated uplands, is essential to support the aquatic functions of the vernal pool habitat. Although the uplands are not actually occupied by vernal pool crustaceans, they nevertheless are essential to the conservation of vernal pool habitat and crustaceans because they maintain the aquatic phase of vernal pools and swales. Associated uplands are also essential to provide nutrients that form the basis of the vernal pool food chain, including a primary food source for the vernal pool crustaceans.

We have used vernal pool complexes as the basis for determining populations of vernal pool crustaceans since the species were first proposed for listing. The final rule to list the four vernal pool crustaceans states that “[t]he genetic characteristics of the three fairy shrimp and vernal pool tadpole shrimp, as well as ecological conditions, such as watershed contiguity, indicate that populations of these animals are defined by pool complexes rather than by individual vernal pools' (Fugate 1992, Fugate 1998, King 1996). Therefore, the most accurate indication of the distribution and abundance of the four vernal pool crustaceans is the number of inhabited vernal pool complexes. Individual vernal pools occupied by the four species listed herein are most appropriately referred to as “subpopulations” (59 FR 48137). Our use of vernal pool complexes to define populations of the four listed crustaceans was upheld by the U.S. District Court in post-listing challenge to the listing (Building Industry Association of Superior California). The July 25, 1997, decision stated: “The Court finds that the plaintiffs were on notice that the FWS would consider vernal pool complexes as a basis for determining fairy shrimp populations. The Court also concludes that the use of this methodology was neither arbitrary nor capricious.” The Court of Appeals for the D.C. Circuit upheld the district court's decision, and the Supreme Court has declined to hear the case.

In identifying specific primary constituent elements for each of the four vernal pool crustaceans, we expanded upon the general primary constituent elements described above and focused on the specific habitat requirements of each individual vernal pool crustacean species. These habitat requirements and the specific primary constituent elements for each vernal pool crustacean are described below.

Conservancy Fairy Shrimp Primary Constituent Elements

The Conservancy fairy shrimp is uniquely adapted to the ephemeral conditions of its vernal pool habitat. Helm (1998) found that the life span and maturation rate of Conservancy fairy shrimp did not differ significantly from other fairy shrimp species under the conditions he observed. Helm (1998) found that Conservancy fairy shrimp reached maturity in an average of 46 days, and lived for as long as 154 days. However, aquatic invertebrate growth rates are largely controlled by water temperature and can vary greatly (Eriksen and Brown 1980, Helm 1998). Eriksen and Belk (1999) observe that Conservancy fairy shrimp produce large cohorts of offspring, and is an “especially hyperactive swimmer and filter feeder.” Conservancy fairy shrimp have only been observed to produce one cohort of offspring each wet season (Eriksen and Belk 1999).

Observations suggest this species is generally found in pools that are relatively large and turbid (King et al. 1996, Helm 1998, Eriksen and Belk 1999). Helm (1998) found that most Conservancy fairy shrimp occurrences were generally within vernal pools formed on fertile, basin rim soils. These pool types may be over several acres in size, and are often alkaline. Soil types where the species is known to occur include Anita, Pescadero, Riz, Solano, Edminster, San Joaquin, and Peters soil series.

Conservancy fairy shrimp occur with several other vernal pool crustaceans, including vernal pool fairy shrimp, California linderiella, and vernal pool tadpole shrimp (King et al. 1996, Eriksen and Belk 1999, Helm 1998). In general, Conservancy fairy shrimp have very large populations within a given pool, and is usually the most abundant fairy shrimp when more than one fairy shrimp species is present (Helm 1998, Eriksen and Belk 1999). Conservancy fairy shrimp are eaten by vernal pool tadpole shrimp (Alexander and Schlising 1997), as well as a variety of insect and vertebrate predator species.

When considering the designation of critical habitat for Conservancy fairy shrimp, we focused on the principal biological and physical features that support Conservancy fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions, and their associated uplands. The primary constituent elements for Conservancy fairy shrimp include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for Conservancy fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to large, playa vernal pools often on basin rim landforms and alkaline soils, but which are dry during the summer and do not necessarily fill with water every year; and

(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Conservancy fairy shrimp. We determined the primary constituent elements of critical habitat for Conservancy fairy shrimp based on studies on their habitat and population biology including but not limited to—Eng et al. 1990, Gallagher 1996, Alexander and Schlising 1997, Helm 1998, Eriksen and Belk 1999.

Longhorn Fairy Shrimp Primary Constituent Elements

Longhorn fairy shrimp are known only from three general locations, and each of these sites contain very different types of vernal pool habitats. Longhorn fairy shrimp in Contra Costa and Alameda counties live in small, clear, sandstone outcrop pools. These sandstone pools have a pH near neutral, and very low alkalinity and conductivity (Eriksen and Belk 1999). Water temperatures in these pools have been measured between 10 and 18°C (50 and 64°F). In the other two locations in Merced and San Luis Obispo counties where longhorn fairy shrimp occur, they are found in turbid, alkaline, grassland vernal pools (Helm 1998, Eriksen and Belk 1999). Water temperatures in these grassland vernal pools tend to be warmer, between 10 and 28°C (50.0 to 82.0°F). However, no experimental studies have been conducted to determine the specific habitat requirements of longhorn fairy shrimp, and until research addressing the tolerance of longhorn fairy shrimp to a range of temperatures and water chemistries, its potential to occur in other types of vernal pool habitats cannot be ruled out.

Like other fairy shrimp, longhorn fairy shrimp are highly adapted to the variable conditions of vernal pool habitats. Longhorn fairy shrimp require a minimum of 23 days, but averaged 43 days, to reach maturity in artificial pools described by Helm (1998). However, Helm (1998) found no significant differences between the life span or reproductive rate of longhorn fairy shrimp and other species of fairy shrimp he studied.

When considering the designation of critical habitat for longhorn fairy shrimp, we focused on the principal biological and physical features that support longhorn fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for the longhorn fairy shrimp include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for longhorn fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to sandstone outcrop pools and turbid alkaline pools, but which are dry during the summer and do not necessarily fill with water every year; and

(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for longhorn fairy shrimp. We determined the primary constituent elements of critical habitat for longhorn fairy shrimp based on studies on their habitat and population biology including but not limited to— Eng et al. 1990, Fugate 1992, Gallagher 1996, Fugate 1998, Helm 1998, and Eriksen and Belk 1999.

Vernal Pool Fairy Shrimp Primary Constituent Elements

Vernal pool fairy shrimp generally will not hatch until water temperatures drop to below 10°C (50°F) (Gallagher 1996, Helm 1998). Vernal pool fairy shrimp are capable of hatching multiple times within a single wet season if conditions are appropriate. Helm (1998) observed 6 separate hatches of vernal pool fairy shrimp within a single wet season, and Gallagher (1996) observed 3 separate hatches of vernal pool fairy shrimp in vernal pools in Butte County.

Vernal pool fairy shrimp have been documented to live for as long as 147 days Helm (1998), but their life cycle and longevity is dependant upon water temperature as well as other environmental factors. Vernal pool fairy shrimp can reproduce in as few as 18 days at optimal conditions of 20°C (68°F) and can complete their life cycle in as little as 63 days (Gallagher 1996, Helm 1998). However, maturation and reproduction rates of vernal pool crustaceans are controlled by water temperature and can vary greatly (Eriksen and Brown 1980, Helm 1998). Helm (1998) observed that vernal pool fairy shrimp did not reach maturity until 41 days at water temperatures of 15°C (59°F). Vernal pool fairy shrimp have been collected at water temperatures as low as 4.5°C (40°F) (Eriksen and Belk 1999), however, the species has not been found in water temperatures above about 23°C (73°F) (Helm 1998, Eriksen and Belk 1999).

Vernal pool fairy shrimp occupy a variety of different vernal pool habitats, from small, clear, sandstone rock pools to large, turbid, alkaline, grassland valley floor pools (Eng et al. 1990, Helm 1998, CNDDB 2001). The pool types where the species has been found include Northern Hardpan, Northern Claypan, Northern Volcanic Mud Flow, and Northern Basalt Flow vernal pools which formed on a variety of geologic formations and soil types (CNDDB 2001). Although vernal pool fairy shrimp have been collected from large vernal pools, including one exceeding 10 ha (25 ac) in area (Eriksen and Belk 1999), they are most frequently found in pools measuring less than 0.02 ha (0.05 ac) in area (Helm 1998, Gallagher 1996). The species occurs at elevations from 10 m (33 ft) to 1,220 m (4,003 ft) (Eng et al. 1990), and is typically found in pools with low to moderate amounts of salinity or total dissolved solids (Keeley 1984, Syrdahl 1993). Vernal pools are mostly rain fed, resulting in low nutrient levels and dramatic daily fluctuations in pH, dissolved oxygen, and carbon dioxide (Keeley and Zedler 1998). Although there are many observations of the environmental conditions where vernal pool fairy shrimp have been found, there have been no experimental studies investigating the specific habitat requirements of this species.

When considering the designation of critical habitat for vernal pool fairy shrimp, we focused on the principal biological and physical features that support vernal pool fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for vernal pool fairy shrimp include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to Northern Hardpan, Northern Claypan, Northern Volcanic Mud Flow, and Northern Basalt Flow vernal pools formed on a variety of geologic formations and soil types, but which are dry during the summer and do not necessarily fill with water every year; and

(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for one of these species. We determined the primary constituent elements of critical habitat for vernal pool fairy shrimp based on studies on their habitat and population biology including but not limited to—Eng et al. 1990, Fugate 1992, Gallagher 1996, Fugate 1998, Helm 1998, and Eriksen and Belk 1999.

Vernal Pool Tadpole Shrimp Primary Constituent Elements

Although the vernal pool tadpole shrimp is adapted to survive in ephemeral vernal pool habitat, the species has a relatively long life span compared to other vernal pool crustaceans. Helm (1998) found that vernal pool tadpole shrimp lived significantly longer than any other species observed under the same conditions except California linderiella (Linderiella occidentalis). Vernal pool tadpole shrimp continue growing throughout their lives, periodically molting their shells. These shells can often be found in vernal pools where the species occurs. Helm (1998) found that vernal pool tadpole shrimp took a minimum of 25 days to mature and the mean age at first reproduction was 54 days. Other researchers have observed that vernal pool tadpole shrimp generally take between 21 to 28 days to mature (Ahl 1991, King 1996). Ahl (1991) found that reproduction did not begin until individuals were larger than 10 mm (0.39 in) carapace length. Variation in growth and maturation rates may be a result of differences in water temperature, which strongly influences the growth rates of aquatic invertebrates.

Vernal pool tadpole shrimp occur in a wide variety of vernal pool habitats (Helm 1998). They have been found in pools with water temperatures ranging from 10°C (50°F) to 29°C (84°F) and pH ranging from 6.2 to 8.5 (Syrdahl 1993, King 1996). However, vernal pools exhibit daily and seasonal fluctuations in pH, temperature, dissolved oxygen, and other water chemistry characteristics (Syrdahl 1993, Scholnick 1995, Keeley 1998a). Determining vernal pool tadpole shrimp habitat requirements is not possible based on anecdotal evidence, and the tolerances of this species to specific environmental conditions have yet to be determined. Although vernal pool tadpole shrimp are found on a variety of geologic formations and soil types, Helm (1998) found that over 50 percent of vernal pool tadpole shrimp occurrences were on high terrace landforms and Redding and Corning soils. Platenkamp (1998) found that vernal pool tadpole shrimp presence differed significantly between geomorphic surfaces at Beale Air Force Base and the species was most likely to be found on Riverbank formation.

When considering the designation of critical habitat for vernal pool tadpole shrimp, we focused on the principal biological and physical features that support vernal pool tadpole shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for vernal pool fairy shrimp include:

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool tadpole shrimp incubation, reproduction, dispersal, feeding, and sheltering, but which are dry during the summer and do not necessarily fill with water every year; including but not limited to vernal pools on Redding and Corning soils on high terrace landforms, and

(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for vernal pool tadpole shrimp. We determined the primary constituent elements of critical habitat for vernal pool tadpole shrimp based on studies on their habitat and population biology including but not limited to—Longhurst 1955, Lynch 1966, Ahl 1991, King 1996, and Helm 1998.

General Primary Constituent Elements for Vernal Pool Plants

The primary constituent elements of critical habitat for vernal pool plants are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. All of the vernal pool plants addressed in this proposed rule are found only in ephemeral wetlands including vernal pools and swales. None of these species are known to occur in permanent wetlands, and none are found in strictly upland areas that are never inundated.

Generally, we identified two primary constituent elements for all eleven vernal pool plants addressed in this proposed rule. Each species has primary constituent elements that differ slightly from these general elements discussed in later sections of this rule. We determined that these proposed primary constituent elements of critical habitat provide for the physiological and ecological requirements of the vernal pool plants.

The first primary constituent element provides the necessary soil moisture and aquatic environment required for seed germination, growth and maturation, reproduction, and dispersal, and the appropriate periods of dry-down for seed dormancy. Both the wet and dry phases of the vernal pool help to reduce competition with strictly terrestrial or strictly aquatic plant species. The wet phase provides the necessary cues for germination and growth, while the drying phase allows the vernal pool plants to flower and produce seeds. We conclude this element is essential to the conservation of the vernal pool plants because these species are ecologically dependent on seasonal fluctuations, such as absence or presence of water during specific times of the year, and duration of inundation and the rate of drying of their habitats. They cannot persist in perennial wetlands or wetlands that are inundated for the majority of the year, nor can they persist without periodic seasonal inundation.

The second primary constituent element is essential to maintain both the aquatic phase and the drying phase of the vernal pool habitat. Although the vernal pool plants addressed in this proposed rule do not occur in the strictly upland areas surrounding vernal pools, they are dependent on these upland areas to maintain the aquatic and drying phases of the vernal pool. The germination of vernal pool plants is dependant on the timing and length of inundation of the vernal pool. The rate of vernal pool drying, during which vernal pool plants must flower and produce seeds, is also largely controlled by interactions between the vernal pool and the surrounding uplands (Hanes et al. 1990, Hanes and Stromberg 1998).

In identifying specific primary constituent elements for each of the eleven vernal pool plant species addressed in this proposed rule, we expanded upon the general primary constituent elements described above to focus on the specific habitat requirements of each of the eleven individual species. These habitat requirements and the specific primary constituent elements for each species are described below.

Butte County Meadowfoam Primary Constituent Elements

The swales and vernal pools where Butte County meadowfoam grows are on intermediate fan terraces (Kelley and Associates Environmental Sciences 1992) in annual grasslands with a mima mound topography. Large cobbles are present throughout the pools and swales (Jokerst 1989). These pools are associated with Tuscan, Redbluff, Riverbank, and Modesto geologic formations, and most of them occur on soils of the Tuscan-Anita and the Redding-Igo complexes. Anita and Igo soils are confined to the pools and swales. Tuscan and Redding soils are restricted to the mounds. Anita soils can be up to 50 cm (19.7 in) deep, whereas Igo soils are no more than 18 cm (7.1 in) deep; the two soils are underlain by iron-silica cemented and indurated hardpan, respectively (Kelley and Associates Environmental Sciences 1993). Butte County meadowfoam has been observed on Anita clay soils annually regardless of rainfall but appears on Igo soils only in years of above average rainfall (Kelley and Associates Environmental Sciences 1992a, Crompton 1993, Schonholtz in litt. 1995), presumably because the former can hold approximately twice as much moisture (Kelley and Associates Environmental Sciences 1993). Confirmed occurrences have been found at 50 to 90 m (165 to 300 ft) in elevation (McNeill and Brown 1979, CNDDB 2001).

The primary constituent elements of critical habitat for Butte County meadowfoam are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Butte County meadowfoam include:

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Butte County meadowfoam germination, growth and reproduction, including but not limited to vernal pool swales and the margins of vernal pools on the Tuscan, Redbluff, Riverbank, and Modesto geologic formations underlain by Tuscan-Anita and Igo-Redding complex soils among others. These habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Butte County meadowfoam germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Butte County meadowfoam. We determined the primary constituent elements of critical habitat for Butte County meadowfoam based on studies of their habitat and population biology including but not limited to—Kalin-Arroyo 1973, Dole 1988, Jokerst 1989, Kelley and Associates Environmental Sciences 1992a, and Crompton 1993.

Contra Costa Goldfields Primary Constituent Elements

Contra Costa goldfields typically grows in vernal pools, swales, moist flats, and depressions within a grassland matrix (CNDDB 2001). However, several historical collections were from populations growing in the saline-alkaline transition zone between vernal pools and tidal marshes on the eastern margin of the San Francisco Bay (Baye USFWS in litt. 2000a). The herbarium sheet for one of the San Francisco Bay specimens notes that the species also grew in evaporating ponds used to concentrate salt (Baye in litt. 2000b). The vernal pool types from which this species has been reported are Northern Basalt Flow, Northern Claypan, and Northern Volcanic Ashflow (Sawyer and Keeler-Wolf 1995). The landforms and geologic formations for sites where Contra Costa goldfields occurs have not yet been determined. Most occurrences of Contra Costa goldfields are at elevations of 2 to 61 m (6 to 200 ft), but the recently discovered Monterey County occurrences are at 122 m (400 ft) and one Napa County occurrence is at 445 m (1,460 ft) elevation (CNDDB 2001).

The soil types that maintain these vernal pool habitats for Contra Costa goldfields have not yet been identified for most localities. The soil series from which it is known are Aiken, Antioch, Concepcion, Conejo, Crispin, Haire, Linne, Los Robles, Rincon, Solano, and San Ysidro, plus the Arnold-Santa Ynez, Hambright-rock outcrop, and Los Osos complexes. Soil textures, where known, are clays or loams. At least in Solano County and on the shores of San Francisco Bay, Contra Costa goldfields grows in alkaline or saline-alkaline sites (Baye in litt. 2000a, Baye in litt. 2000b, CNDDB 2001).

The primary constituent elements of critical habitat for Contra Costa goldfields are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Contra Costa goldfields include—

(1) Vernal pools, swales, moist flats, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Contra Costa goldfields germination, growth and reproduction, including, but not limited to, vernal pools on clay soils from a variety of soils series, rock outcrop pools on basalt flows, and vernal pools in saline alkaline transition zones with tidal marsh habitats. All of these habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Contra Costa goldfields. We determined the primary constituent elements of critical habitat for Contra Costa goldfields based on studies on their habitat and population biology including but not limited to—Ornduff 1966, Ornduff 1979, Crawford and Ornduff 1989, Skinner and Pavlik 1994.

Hoover's Spurge Primary Constituent Elements

Vernal pools from which Hoover's spurge has been reported are classified as Northern Hardpan and Northern Claypan vernal pools (Sawyer and Keeler-Wolf 1995). The pools supporting this species vary in size from 0.19 to 243 ha (0.47 to 600 ac), with a median area of 0.58 ha (1.43 ac) (Stone et al. 1988). Many occurrences consist of multiple pools that vary in area and in depth, yet not all pools at a site support Hoover's spurge. Deeper pools apparently provide better habitat for this species because the duration of inundation is longer. This species may occur along the margins or in the deepest portions of the dried pool bed (Stone et al. 1988, Alexander and Schlising 1997). A particularly important feature of Hoover's spurge microhabitat, at least in the deeper pools, is that it is nearly devoid of other vegetation, and thus competition from other plants is reduced (Stone et al. 1988).

Vernal pools supporting Hoover's spurge occur mostly on alluvial fans or terraces of ancient rivers or streams, with a few on the rim of the Central Valley basin. Hoover's spurge is found on a wide variety of soils, which range in texture from clay to sandy loam. Soil series from which it has been reported include Anita, Laniger, Lewis, Madera, Meikle, Riz, Tuscan, Whitney, Willows. All of these soils may not be equally suitable for this species, however. For example, in one Vina Plains pool, Hoover's spurge grew primarily in the portion that was underlain by Tuscan loam and was nearly absent from the portion underlain by Anita clay (Alexander and Schlising 1997).

In the Sacramento Valley occupied pools are on acidic soils over iron-silica cemented hardpan. Most pools supporting Hoover's spurge in the San Joaquin Valley are on neutral to saline-alkaline soils over lime-silica cemented hardpan or claypan (Broyles 1987, Stone et al. 1988, Sawyer and Keeler-Wolf 1995, CNDDB 2001). Occurrences of Hoover's spurge have been reported from elevations ranging from 26 m (85 ft) in Glenn County to 128 m (420 ft) in Tehama County (CNDDB 2002).

The primary constituent elements of critical habitat for Hoover's spurge are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Hoover's spurge include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Hoover's spurge germination, growth and reproduction, including but not limited to vernal pools formed on neutral to saline-alkaline soils over lime-silica cemented hardpan or claypan, or on acidic soils over iron-silica cemented hardpan, that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Hoover's spurge. We determined the primary constituent elements of critical habitat for Hoover's spurge based on studies on their habitat and population biology including but not limited to—Broyles 1987, Stone et al. 1988, and Alexander and Schlising 1997.

Succulent Owl's-Clover Primary Constituent Elements

Succulent owl's-clover is known mostly from vernal pools occurring on alluvial terrace landforms. These pool types have been described as both Northern Claypan and Northern Hardpan vernal pools (Sawyer and Keeler-Wolf 1995) within annual grassland communities (CNDDB 2001). However, it is found on Northern Basalt Flow vernal pools on Hideaway soils series at one location in the San Joaquin Valley. It is known from both small and large pools (EIP Associates 1999). Although not all pools occupied by this taxon have been studied in detail, Stebbins et al. (1995) collected data on six occupied pools in Fresno and Madera counties. Some were typical “bowl-like” pools, whereas others were more similar to swales. This subspecies has been reported from pools with both long and short inundation periods (EIP Associates 1999) and from both shallow and “abnormally deep vernal pools,” but approximate depth of these pools was not given (CNDDB 2001).

Soil series supporting succulent owl's-clover include Amador, Anderson, Corning, Fallbrook, Keyes, Pentz, Ramona, Redding, San Joaquin, Vista, and Yokohl, as well as the Pollasky-Montpellier complex. Soil textures at those sites range from extremely stony loam to loamy clay. In the proposed UC Merced campus and community area, the species is found primarily on Redding gravelly loam; however, Corning, Keyes, and Pentz soils also contain occurrences of the species (EIP Associates 1999). Populations of succulent owl's-clover have been reported from elevations of 24 m (80 ft) at the San Joaquin County site to 700 m (2,300 ft) at Kennedy Table in Madera County (CNDDB 2001).

The primary constituent elements of critical habitat for succulent owl's-clover are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for succulent owl's-clover include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain succulent owl's-clover germination, growth and reproduction, including but not limited to hardpan vernal pools on alluvial terraces and San Joaquin, Redding, Corning, Keyes, and Pentz soils series, among others, and northern basalt flow vernal pools on Hideaway soils series, that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for succulent owl's-clover germination, growth, reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for succulent owl's-clover. We determined the primary constituent elements of critical habitat for succulent owl's-clover based on studies of their habitat and population biology including but not limited to—Hoover 1968, Chuang and Heckard 1991, Chuang and Heckard 1993, and EIP Associates 1999.

Colusa Grass Primary Constituent Elements

Colusa grass has the broadest ecological range among the Orcuttieae. It occurs on the rim of alkaline basins in the Sacramento and San Joaquin valleys, as well as on acidic soils of alluvial fans and stream terraces along the eastern margin of the San Joaquin Valley and into the adjacent foothills (Stone et al. 1988). Colusa grass has been found in Northern Claypan and Northern Hardpan vernal pool types (Sawyer and Keeler-Wolf 1995) within rolling grasslands (Crampton 1959). This species typically grows in the deepest portion of the pool (Crampton 1959) but also may occur on the margins (Hoover 1937, Stone et al. 1988). Deeper pools are most likely to provide the long inundation period required for germination (EIP Associates 1999).

Several soil series maintain the vernal pool habitats where Colusa grass is found. Solano and Yolo county sites where Colusa grass grows contain vernal pools formed by soils in the Pescadero series, whereas those in central Merced County are formed by soils in the Landlow and Lewis series (Silveira in litt. 2000). The eastern Merced County and Stanislaus County sites include vernal pool habitats formed by the Bear Creek, Corning, Greenfield, Keyes, Meikle, Pentz, Peters, Raynor, Redding, and Whitney series (Stone et al. 1988, EIP Associates 1999, CNDDB 2002). The type and composition of impermeable layers underlying occupied vernal pools also vary, ranging from claypan in the Sacramento Valley to lime-silica cemented hardpan in the San Joaquin Valley basins, to iron-silica cemented hardpan in the eastern margin of the San Joaquin Valley. Tuffaceous alluvium underlies some eastern San Joaquin Valley pools and intermittent streams where Colusa grass grows (Stone et al. 1988).

The primary constituent elements of critical habitat for Colusa grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Colusa grass include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Colusa grass germination, growth and reproduction, and that typically become inundated during winter rains, including but not limited to vernal pools formed on the rim of alkaline basins in the Sacramento and San Joaquin valleys, as well as on acidic soils of alluvial fans and stream terraces along the eastern margin of the San Joaquin Valley and into the adjacent foothills. All of these pool types are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Colusa grass germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Colusa grass. We determined the primary constituent elements of critical habitat for Colusa grass based on studies on their habitat and population biology including but not limited to—Crampton 1976, Griggs 1980, Reeder 1982, Griggs and Jain 1983, Keeley 1998a, and Stone et al. 1988.

Greene's Tuctoria Primary Constituent Elements

Greene's tuctoria has been found in three types of vernal pools: Northern Basalt Flow, Northern Claypan, and Northern Hardpan (Sawyer and Keeler-Wolf 1995, Stone et al. 1988). Occupied pools are or were underlain by iron-silica cemented hardpan, tuffaceous alluvium, or claypan (Stone et al. 1988). Of pools where the species was known to be extant in 1987, the median size was 0.6 ha (1.5 ac), with a range of 50 m2 (0.01 ac) to 3.4 ha (8.4 ac) (Stone et al. 1988). Stone et al. (1988) noted that Greene's tuctoria grew in shallower pools than other members of the tribe or on the shallow margins of deeper pools, but they did not quantify pool depth. At the Vina Plains, Greene's tuctoria grew in pools of “intermediate” size, which dried in April or early May of 1995 (Alexander and Schlising 1997). The Central Valley pools containing Greene's tuctoria are (or were) in grasslands; the Shasta County occurrence is surrounded by pine forest (CNDDB 2001). Occupied pools in the Central Valley are (or were) at elevations of 33.5 to 134 m (110 to 440 ft) (Stone et al. 1988), whereas the Shasta County occurrence is at 1,067 m (3,500 ft) (CNDDB 2001).

In Tehama and Butte counties, Greene's tuctoria grows mostly on Anita clay and Tuscan loam soils, with one occurrence on Tuscan stony clay loam. Soil types are not certain for several other occurrences in this region; one is on either the Rocklin or the San Joaquin series, and the others are unknown. The single occurrence in the central portion of the Central Valley, near the Glenn and Colusa county line, is on strongly saline-alkaline Willows clay (Silveira in litt. 2000). On the eastern margin of the San Joaquin Valley, Greene's tuctoria is known to grow on a number of different soil series including Archerdale, Bear Creek, Exeter, Meikle, Ramona, Raynor, Redding, and San Joaquin.

The primary constituent elements of critical habitat for Greene's tuctoria are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Greene's tuctoria include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Greene's tuctoria germination, growth and reproduction, including but not limited to Northern Claypan, Northern Hardpan and Northern Basalt flow vernal pools, that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Greene's tuctoria. We determined the primary constituent elements of critical habitat for Greene's tuctoria based on studies on its habitat and population biology including but not limited to—Griggs 1980, Griggs and Jain 1983, Stone et al. 1988, Keeley 1988, and Alexander and Schlising 1997.

Hairy Orcutt Grass Primary Constituent Elements

This species is found within vernal pools formed on high or low stream terraces and alluvial fans (Stone et al. 1988). The median size of occupied pools measured in the late 1980's was 1.7 ha (4.2 ac), with a range of 0.34 to 250 ha (0.8 to 617.5 ac) (Stone et al. 1988). At the Vina Plains, hairy Orcutt grass was found growing only in pools that held water until May, June, or July in 1995, not in those that dried in April (Alexander and Schlising 1997). This species is known from elevations of 26 m (85 ft) in Glenn County to 123 m (405 ft) in Madera County (CNDDB 2001).

Hairy Orcutt grass is found on both acidic and saline-alkaline soils, in pools with an iron-silica cemented hardpan or claypan. In Tehama and Butte counties, pools supporting hairy Orcutt grass occur on the Anita and Tuscan soil series (Stone et al. 1988, CNDDB 2001). At one pool in the Vina Plains that spans both Anita clay and Tuscan loam soils, hairy Orcutt grass was found growing primarily on the Anita clay (Alexander and Schlising 1997). At the Sacramento National Wildlife Refuge, hairy Orcutt grass occurs on the Willows and Riz soil series (Silveira in litt. 2000), whereas in the Southern Sierra Foothills Vernal Pool Region it occurs on the Cometa, Greenfield, Hanford, Meikle, and Whitney soil series (Stone et al. 1988).

The primary constituent elements of critical habitat for hairy Orcutt grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for hairy Orcutt grass include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain hairy Orcutt grass germination, growth and reproduction, including but not limited to features occurring on both acidic and saline-alkaline soils, with an iron-silica cemented hardpan or claypan, and that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool plant germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for hairy Orcutt grass. We determined the primary constituent elements of critical habitat for hairy Orcutt grass based on studies on their habitat and population biology including but not limited to—Crampton 1959, Medeiros, 1976, Griggs 1980, Griggs and Jain 1983, Stone et al. 1988, Durgarian 1995, and Alexander and Schlising 1997.

Sacramento Orcutt Grass Primary Constituent Elements

Sacramento Orcutt grass has been found in Northern Hardpan and Northern Volcanic Mudflow vernal pools (Sawyer and Keeler-Wolf 1995). It occurs on high terrace sites (Stone et al. 1988) at elevations of 46 to 82 m (150 to 270 ft) (CNDDB 2001). Occupied pools occur in blue oak woodland and annual grassland (Crampton 1959, Griggs 1977, CNDDB 2002). Among occupied pools discovered prior to 1988, the median area was 0.28 ha (0.69 ac) and ranged from 0.1 ha (0.25 ac) to 0.82 ha (2.03 ac). Soils underlying pools where Sacramento Orcutt grass grows are acidic with an iron-silica hardpan (Stone et al. 1988), and the pools contain numerous cobbles (Crampton 1959, Stone et al. 1988). Four of the known occurrences are on soils in the Redding series, two are on Red Bluff-Redding complex soils, two are (or were) on Xerarents-urban land-San Joaquin complex, and one is on Corning complex soils.

The primary constituent elements of critical habitat for Sacramento Orcutt grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Sacramento Orcutt grass include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Sacramento Orcutt grass germination, growth and reproduction, including but not limited to vernal pools on high terrace landforms on acidic soils such as Red Bluff, Redding, and Corning soil series. These habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Sacramento Orcutt grass germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Sacramento Orcutt grass. We determined the primary constituent elements of critical habitat for Sacramento Orcutt grass based on studies on their habitat and population biology including but not limited to—Crampton 1959, Griggs 1980, Griggs and Jain 1983, Holland 1987, and Stone et al. 1988.

San Joaquin Valley Orcutt Grass Primary Constituent Elements

San Joaquin Valley Orcutt grass occurs on alluvial fans, high and low stream terraces (Stone et al. 1988), and tabletop lava flows (Stebbins et al. 1995, CNDDB 2001). This species has been reported in Northern Claypan, Northern Hardpan, and Northern Basalt Flow vernal pools (Sawyer and Keeler-Wolf 1995) within rolling grassland (Crampton 1959). Occupied pools range in surface area from 0.014 to 4.9 ha (0.05 to 12.1 ac), with a median area of 0.62 ha (1.54 ac) (Stone et al. 1988). San Joaquin Valley Orcutt grass has been reported from elevations of 30 to 755 m (100 to 2,475 ft); the highest elevation sites are those on the volcanic tabletops of Fresno and Madera counties (Stebbins et al. 1995, CNDDB 2001).

The pools where San Joaquin Valley Orcutt grass is known to occur form on acidic soils that vary in texture from clay to sandy loam. Soil series represented include the Hideaway series on Fresno-Madera County volcanic tabletops, and Amador, Cometa, Corning, Greenfield, Los Robles, Madera, Peters, Pollasky-Montpellier complex, Raynor, Redding, and San Joaquin soil series elsewhere in the range. The impermeable layer at historical or extant occurrences included iron-silica cemented hardpan, tuffaceous alluvium, and basaltic rock from ancient volcanic flows (Stone et al. 1988, Stebbins et al. 1995, EIP Associates 1999, CNDDB 2001).

The primary constituent elements of critical habitat for San Joaquin Valley Orcutt grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for San Joaquin Valley Orcutt grass include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain San Joaquin Orcutt grass germination, growth and reproduction, including but not limited to vernal pools on alluvial fans, high and low stream terraces, and tabletop lava flows. These habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for San Joaquin Valley Orcutt grass germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for San Joaquin Valley Orcutt grass. We determined the primary constituent elements of critical habitat for San Joaquin Valley Orcutt grass pools based on studies on their habitat and population biology including but not limited to—Crampton 1959, Griggs 1980, Griggs and Jain 1983, Stone et al. 1988, Stebbins et al. 1995, Keeley 1998a, and EIP Associates 1999.

Slender Orcutt Grass Primary Constituent Elements

Slender Orcutt grass is found primarily on substrates of volcanic origin (Crampton 1959, Corbin and Schoolcraft 1989). Vernal pools in which slender Orcutt grass grows are classified as Northern Volcanic Ashflow and Northern Volcanic Mudflow vernal pools (Sawyer and Keeler-Wolf 1995). Impervious layers range from iron-silica hardpan to bedrock (Stone et al. 1988, Corbin and Schoolcraft 1989, CNDDB 2001). Among the populations studied by Stone and others (1988), the median area of pools occupied by slender Orcutt grass was 0.65 ha (1.6 ac) and ranged from 0.08 to 45 ha (0.2 to 111 ac). On the Modoc Plateau, occupied pools known as of 1989 ranged in size from 2 to 40 ha (5 to 100 ac) and were typically at least 30 cm (11.8 in) deep; this species was restricted to the deepest areas of these pools (Corbin and Schoolcraft 1989). Slender Orcutt grass occurs through a wide range of elevations corresponding to its broad geographical range. The lowest reported elevation was 27 m (90 ft) in Sacramento County (Stone et al. 1988) and the highest was 1,756 m (5,761 ft) in Plumas County (Corbin in litt. 1999).

Soil types supporting vernal pools where slender Orcutt grass is known to occur are diverse, ranging from slightly to strongly acidic (Stone et al. 1988) and from clay to sandy, silty, or cobbly loam (Corbin and Schoolcraft 1989, CNDDB 2001). The soil series has not been reported for all slender Orcutt grass sites but the species has been reported on Collayomi-Aiken-Whispering complex and the Konocti-Hambright complex soils. Modoc Plateau occurrences occur on the Gooval, Lasvar, Lasvar-Pitvar complex, and Nosoni soil series, whereas occurrences in northeastern Sacramento Valley are on the Anita, Guenon, Inks, Inskip, Laniger, Moda, Redding, Toomes, and Tuscan soil series. The Redding soil series also supports slender Orcutt grass in Sacramento County (Stone et al. 1988, CNDDB 2001).

Vegetation types in which the occupied pools occur are diverse, ranging from grassland and oak woodland to mixed conifer forest, silver sagebrush (Artemisia cana) flats, and sedge meadows (Crampton 1959, CNDDB 2001). Associated species vary throughout the range of slender Orcutt grass. Although slender Orcutt grass grows in the same vernal pool complexes as hairy Orcutt grass in Tehama County (including the Vina Plains Preserve) and Sacramento Orcutt grass in Sacramento County, it has not been found to share any pools with either species (Stone et al. 1988, Cochrane in litt. 1995a, Alexander and Schlising 1997, CNDDB 2001).

The primary constituent elements of critical habitat for slender Orcutt grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for slender Orcutt grass include—

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain slender Orcutt grass germination, growth and reproduction, including but not limited to Northern Volcanic Ashflow and Northern Volcanic Mudflow vernal pools (Sawyer and Keeler-Wolf 1995) with iron-silica and bedrock hardpan impervious layers, and that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for slender Orcutt grass. We determined the primary constituent elements of critical habitat for slender Orcutt grass based on studies on their habitat and population biology including but not limited to—Griggs 1980, Griggs 1981, Reeder 1982, Griggs and Jain 1983, Stone et al. 1988, Corbin and Schoolcraft 1989, and Alexander and Schlising 1997.

Solano Grass Primary Constituent Elements

Solano grass has been found only in the Northern Claypan type of vernal pool (Sawyer and Keeler-Wolf 1995) within annual grassland (CNDDB 2001). Pools where Solano grass occurs tend to be milky from suspended sediments (Holland 1987). The occupied pools in Solano County are more properly described as alkaline playas or intermittent lakes due to their large surface area (Crampton 1959), whereas those at the Yolo County site are “relatively small” (Witham in litt. 2000a). Soils underlying known Solano grass sites are saline-alkaline clay or silty clay in the Pescadero series (Crampton 1959, CNDDB 2001). Known occurrences are at elevations of approximately 5 to 11 m (15 to 35 ft) (CNDDB 2001).

The primary constituent elements of critical habitat for Solano grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Solano grass include:

(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Solano grass germination, growth and reproduction, including but not limited to Northern Claypan vernal pools (Sawyer and Keeler-Wolf 1995) on saline-alkaline clay or silty clay in the Pescadero soil series that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and

(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Solano grass germination, growth and reproduction, and dispersal, but not necessarily every year.

All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Solano grass. We determined the primary constituent elements of critical habitat for Solano grass based on studies on their habitat and population biology including but not limited to—Griggs 1980, Holland 1987, and Stone et al. 1988.

Criteria Used To Identify Critical Habitat

In accordance with section 3(5)(A)(I) of the Act and regulations at 50 CFR 424.12 in determining which areas to propose as critical habitat, we are required to base critical habitat determinations on the best scientific and commercial data available and to consider those physical and biological features that are essential to the conservation of the species and that may require special management considerations or protection. Such requirements include but are not limited to: space for individual and population growth, and for normal behavior; food, water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, rearing of offspring; and habitats that are protected from disturbance or are representative of the historic geographical and ecological distributions of a species. Our implementing regulations at 50 CFR 424.12(e) indicate that the Secretary shall designate as critical habitat areas outside the geographical area presently occupied by a species only when a designation limited to its present range would be inadequate to ensure the conservation of the species.

The primary objective in designating critical habitat is to identify areas that are considered essential for the conservation of the species, and to highlight specific areas where special management considerations or protections are necessary. The Act defines the term “conservation” to mean “the use of all methods and procedures which are necessary to bring any endangered species or threatened species to the point at which the measures provided pursuant to this Act are no longer necessary. Such methods and procedures include, but are not limited to, all activities associated with scientific resources management such as research, census, law enforcement, habitat acquisition and maintenance, propagation, live trapping, and transplantation * * * ” Section 4(f)(1) of the Act provides for the development and implementation of recovery plans “for the conservation and survival of endangered species and threatened species,” and directs that such plans incorporate “a description of such site-specific management actions as may be necessary to achieve the plan's goal for the conservation and survival of the species;” and “objective, measurable criteria which, when met, would result in a determination * * * that the species be removed from the list.”

General Criteria

The Service currently is preparing a draft recovery plan that will describe measures and actions necessary for the conservation and survival of the vernal pool species addressed in this proposed rule. In determining the size, number, and location of areas to propose as critical habitat we have considered the features necessary for conservation of each species as recommended by the vernal pool recovery team, other vernal pool experts, peer reviewed literature, scientific reports, and other information in our files. We do not, however, anticipate that these areas include all of the habitat areas that may eventually be determined to be necessary for the conservation of the species addressed herein. For these reasons, critical habitat designations do not signal that habitat outside the designation is unimportant or may not be required for recovery.

The conservation of species addressed in this rule depends on removing and alleviating the factors that threaten them, including factors that led to their population decline and subsequent Federal listing. Most species addressed in this proposed rule are threatened by common factors because they occupy the same vernal pool ecosystems.

Holland (1998) estimated that almost three-quarters of vernal pool habitats in the Central Valley of California had been lost by 1997. Loss of habitat has been even more complete in areas outside of the Central Valley. In the central coast area, at least 90 percent of historic vernal pools have been destroyed, and most remaining pools have been degraded (Ferren and Pritchett 1988). In southern California estimated loss of vernal pool habitat ranges from 95 percent to nearly total (Bauder 1986, 1987, Bauder and McMillan 1998). In Oregon, 60 percent of vernal pool habitats have been destroyed, and only 18 percent of the remaining habitats are considered intact (Oregon Natural Heritage Program 1997, Borgias and Patterson 1999). As a result of widespread habitat loss, most of the species addressed in this rule are now limited to a fraction of their former ranges.

Beginning around the mid-1800s, vernal pool habitats were destroyed as a result of conversion to agriculture and water diversion and impoundment projects (Frayer et al. 1989, Holland 1998, Kreissman 1991). In more recent years, vernal pool habitats have been lost primarily as a result of widespread urbanization (Bauder 1986, Bauder and McMillan 1998). Much of the loss of habitat was the result of residential, commercial, and industrial development projects. The construction of infrastructures associated with urbanization has also contributed greatly to loss of vernal pool habitats, including the construction of highways, wastewater treatment plants, sewer lines, water supply projects, and other utility projects associated with urbanization in California.

In some areas, conversion of vernal pool habitats to intensive agricultural uses continues to contribute to the decline of vernal pool habitats and the species that inhabit them. From 1992 to 1998, 50,825 ha (125,591 ac) of grazing land were converted to other agricultural uses in the Central Valley of California (California Department of Conservation 2001). It is likely that much of this land supported vernal pools. Holland estimated that more than 12,950 ha (32,000 ac) of vernal pool habitats had been lost in the San Joaquin valley vernal pool region from the late 1980s until 1997, mostly as a result of agricultural conversion (Holland 1998). Through consultation under section 7 of the Act, we reviewed projects converting more than 6,070 ha (15,000 ac) of vernal pool habitats to intensive agricultural uses.

Vernal pool species are also threatened by other activities that indirectly destroy vernal pool ecosystems and render them unsuitable for vernal pool species, including activities that alter hydrology, introduce contaminants, cause erosion or sedimentation, and introduce non-native species into vernal pool ecosystems. Maintaining habitat integrity was identified by the vernal pool recovery team as an important consideration in planning recovery strategies for the species addressed in this proposed rule (Vernal Pool Recovery Team in litt. 1996). The recovery of the species addressed in this proposed rule will depend on the development of recovery strategies that eliminate or minimize these threats so that populations can stabilize, and future declines will be minimized.

Alteration of vernal pool hydrology can dramatically degrade vernal pool habitats. Vernal pool hydrology can be altered by a variety of activities, including the construction of roads, trails, ditches, or canals that can block the flow of water into, or drain water away from, vernal pools and vernal pool complexes (CNDDB 2001). Runoff from irrigated agricultural lands, storm water drains, or developed areas covered with concrete, asphalt, or irrigated lawns can dramatically alter the hydrology of adjacent vernal pools (Bauder 1987, Clark et al. 1998). As described in the primary constituent element section of this rule, all of the species addressed herein depend on specific timing and duration of inundation to complete their life cycles. Altered vernal pool hydrology can harm vernal pool species by preventing germination or hatching, preventing growth and maturation, and by preventing reproduction and disrupting gene flow and dispersal. Altered hydrology can also allow invasion of habitats and extirpation of vernal pool species by dominant upland or aquatic species.

Vernal pool species have also declined as a result of water contamination. Vernal pool crustaceans, in particular are highly sensitive to the water chemistry of their vernal pool habitats, and contamination of vernal pools may injure or kill them (Belk 1977, Eng et al. 1990, Gonzalez et al. 1996). Toxic chemicals, such as petroleum products, pesticides, herbicides, adjuvants, fertilizers, and soap may wash into vernal pools during development of adjacent areas. Vernal pools adjacent to existing developments may also be contaminated from roadway contaminants in surface runoff (e.g., grease, oil, and heavy metals). Contamination may result from discharge of fertilizers and pesticides into surface waters from golf courses, irrigated agricultural lands, or landscaped residential areas (Petrovic 1990). In addition to altered hydrology and contamination, vernal pool species have declined as a result of a variety of other incompatible land uses including off road vehicle use, dumping, vandalism, erosion and sedimentation (Service 1994c, CNDDB 2001).

Additional threats to vernal pool species include the negative effects of fragmentation and isolation on populations that were once part of larger interconnected habitats, and the effects of small population sizes and loss of genetic diversity that result from habitat fragmentation. Fragmentation threatens the elimination of some populations with unforeseen natural and anthropogenic catastrophic events. Vernal pool species in these small habitat patches are also vulnerable to random fluctuations in habitat availability due to annual weather patterns and other environmental factors. They are also more vulnerable to extirpation from random fluctuations in demographic factors, such as birth rates and death rates (Lesica and Allendorf 1995).

Fragmentation of vernal pool complexes could contribute significantly to the loss of genetic diversity among vernal pool species and reduce the likelihood of recolonization events following population extinction by limiting opportunities for dispersal (King 1996, Fugate 1998). The fragmentation of vernal pool habitats may decrease the ability of avian species to move between remaining patches of vernal pool habitats (Silveira 1998), which would contribute to the isolation of vernal pool crustacean populations by reducing cyst dispersal between remaining vernal pool habitat patches (Proctor 1964, Krapu 1974, Swanson 1974, Driver 1981, Ahl 1991). Fragmentation of vernal pool areas could reduce the availability of habitat for pollinator species, and decrease or eliminate seed production of many vernal pool plants (Thorp and Leong 1998).

As described in the Primary Constituent Element section of this proposed rule, the conservation of the wetted area of the vernal pool alone is not sufficient to provide the hydrologic conditions necessary for the reproduction, feeding, sheltering, and dispersal of the vernal pool species addressed in this proposed rule. To maintain the integrity of the vernal pool habitat and prevent extirpation of vernal pool species resulting from altered hydrology, contamination, sedimentation, and other factors which originate in the uplands surrounding the vernal pools it is equally necessary to conserve the surrounding micro-watershed and associated uplands that directly surround and feed the wetted area of the vernal pool or pool complex.

The boundaries of vernal pool complexes, including vernal pools, swales, and the associated uplands, where vernal pool species are known to occur in California have been mapped by Holland (1998, 2002) and by a number of local and state organizations throughout California and in Oregon. The soil types and geologic formations which support vernal pools have also been mapped, and the associated landforms have been identified. We utilized these boundaries to identify areas that support vernal pools, swales, and the associated uplands that comprise the hydrological unit of the vernal pool complex necessary for vernal pool crustacean growth, reproduction, feeding, and dispersal and vernal pool plant germination, growth, and reproduction. We relied on these mapped boundaries to identify vernal pool complexes as intact, hydrologically functioning units. We did not dissect or fragment existing complexes within this designation. However, we do not believe the entire watershed of vernal pool habitats, as depicted by CALWATER or other watershed mapping efforts, is essential to the conservation of the species, and we are not proposing to designate entire watersheds as critical habitat.

Maintaining the range of habitat types in which a species is known to occur has been identified as an important element in species recovery (Vernal Pool Recovery Team in litt. 1996). Protecting environmental variability will reduce the chance of losing populations that are important for their genetic uniqueness and adaptation to local environmental conditions (Fugate 1992, King 1996, Linhart and Grant 1996, Fugate 1998). Environmental factors such as hydrology, soil composition and chemistry, pool size, and water chemistry, play a major role in determining species presence and composition in vernal pool plants (Holland and Griggs 1976, Holland and Dains 1990, Jokerst 1990, Stallings and Warren 1996). The presence and species composition of vernal pool crustaceans is also largely determined by physical factors such as pool size, depth, area, and water chemistry (Eng et al. 1990, Gonzales et al. 1996, Hathaway and Simovich 1996, Simovich and Hathaway 1997, Platenkamp 1998, Simovich 1998, Helm 1998). Variation in these factors contributes to the wide range of life history strategies observed in vernal pool crustaceans and plants, and to the high levels of species diversity observed in vernal pool ecosystems in general. Various efforts to classify vernal pools, including Sawyer and Keeler-Wolf 1995, Keeler-Wolf et al. 1998, Smith and Verrill 1998, have identified the locations and distributions of these different pool types. We consulted these sources of information to ensure we have accurately identified the range of habitats in which each of the 15 species addressed in this proposed rule are known to occur.

Special Management Considerations

In proposing critical habitat, we also have considered how this designation highlights habitat that needs special management considerations or protection. For example, we have many regional HCPs under development, and this designation will be useful in helping applicants determine what vernal pool habitat areas should be highest priority for special management or protection, and where there may be more flexibility in conservation options. This designation will guide them and us in ensuring that all local habitat conservation planning efforts are consistent with conservation objectives for these species.

Once a vernal pool habitat has been protected from direct filling, it is still necessary to ensure that the habitat is not rendered unsuitable for vernal pool species because of factors such as altered hydrology, contamination, non-native species invasions, or other incompatible land uses. Even the best designed vernal pool preserve may still be susceptible to alterations that render it unsuitable for vernal pool species. Many of the factors that cause the decline and extirpation of vernal pool species can be controlled through special management actions. Examples of special management actions that may be necessary to prevent further declines and loss of populations of species addressed in this rule include—

(1) Actions to prevent or reduce competition of vernal pool plants with invasive species. Many of the species addressed in this rule are threatened by invasion of non-native species (CNDDB 2001). Special management actions can be taken to reduce the negative effects of such invasions. For example, grazing can be effectively used to control a variety of upland exotic plants. However, the timing and intensity of grazing is critical to its success as a management tool, and these factors should be closely monitored. Alternatively, inappropriate grazing can also pose a threat to many of the vernal pool plant species (CNDDB 2001). Prescribed burning is another management tool that may be effective in controlling non-native plant species (Pollack and Kan 1998). Fire must also be appropriately timed and fire frequency is important. The potential for alteration of nutrient cycling must be also considered. Other management techniques for control of invasive species include mowing, hand removal, and selective herbicide applications. Any technique employed must be carefully controlled and monitored to ensure that it does not negatively affect the vernal pool species.

(2) Actions to restore vernal pool hydrology. Alteration of natural hydrology threatens many of the species addressed in this proposed rule (CNDDB 2001). In many cases other threats, such as the invasion of non-native species or contamination, are facilitated by alterations of natural vernal pool hydrology. Special management actions, such as the removal of dams or other structures which artificially increase the length of vernal pool inundation, the removal of ditches that artificially drain vernal pools, or the construction of berms or reconstruction of culverts to prevent water from flowing artificially into vernal pools from adjacent areas, can be taken to restore natural vernal pool hydrology. Modification of grazing regimes may also restore natural vernal pool hydrology (Barry 1998). Monitoring of vernal pool hydrology is important to ensure that restoration actions are successful.

(3) Actions to reduce human degradation of vernal pools. Special management actions such as fencing, trail building, and posting signs can help to reduce human activities that threaten vernal pool species. These actions may reduce the damage resulting from off-road vehicle use, dumping, and vandalism that threatens many of the species addressed in this proposed rule.

(4) Actions to restore severely degraded habitats. Active restoration of highly degraded vernal habitats may be necessary in some areas. Such restoration may involve earth moving activities designed to restore historic pool and swale topography and to reestablish natural vernal pool hydrology (e.g., Ferren and Hubbard 1998, Black and Zedler 1998). These types of actions are extremely complex, and require diligent planning and monitoring to ensure their success. Active restoration is only recommended for seriously degraded habitats that otherwise would not maintain natural vernal pool ecosystem processes.

Summary of Proposed Designation

Table 1 shows approximate areas of proposed critical habitat, by unit and species. Because of overlap between units established for different species, the total of all critical habitat proposed is much less than the sum of critical habitat areas proposed for each species. Lands proposed are under private, State, and Federal ownership and divided into 128 Critical Habitat Units. The table provides separate columns for privately owned land subject to conservation easements or agreements and other privately owned lands.

Species Specific Criteria

After developing the general criteria described previously, we conducted a species by species review based on the specific habitat requirements, primary constituent elements, and individual threats to each species addressed in this proposed rule. The specific unit description for each species is described below.

Conservancy Fairy Shrimp Criteria

In proposing critical habitat units for Conservancy fairy shrimp, we evaluated the life history and current distribution of the species described in the background section of this rule, the primary constituent elements described in the primary constituent element section of this rule, and the threats to the species described above, in addition to those described below. This information allowed us to determine which areas are likely to contribute to the conservation of Conservancy fairy shrimp and to delineate units so that threats to these species might be minimized.

Conservancy fairy shrimp are known only from eight disjunct areas: the Vina Plains area and vicinity in southern Tehama and northern Butte County; Jepson Prairie and Suisun Slough in southern Solano County; Sacramento National Wildlife Refuge in Glenn and Colusa counties; near Caswell Memorial State Park in Stanislaus County; near Haystack Mountain in Merced County; at the San Luis National Wildlife Refuge Complex in western Merced County, and at the Mutau Flat area in the Los Padres National Forest area of northern Ventura County.

Conservancy fairy shrimp continues to be threatened by all of the factors which lead to the original listing of this species, primarily habitat loss through agricultural conversion and urbanization. Helm (1998) found that most Conservancy fairy shrimp occurrences were on Anita, Pescadero or Peters Clay soils. These fertile, basin rim soils were among the first areas converted to agriculture in the 19th century, suggesting that a disproportionate amount of Conservancy fairy shrimp habitat may have been lost early in California's history (Helm 1998).

In addition to direct habitat loss, almost one third of the known occurrences of Conservancy fairy shrimp are threatened by alterations of hydrology, including the construction of drainage channels, diking, and inappropriate water diversion within managed wetland areas in Merced and Solano counties (CNDDB 2002). Other threats include possible introduction of predators (e.g., bullfrogs, crayfish, fish) either directly or through alteration of drainage patterns (CNDDB 2002). Off-road vehicles also represent a threat to the continued survival of Conservancy fairy shrimp populations (Hathaway et al. 1996). In some cases, special management actions may be necessary to prevent these threats from extirpating occurrences of Conservancy fairy shrimp.

Conservancy Fairy Shrimp Review

We conducted a regional review across the range of Conservancy fairy shrimp to evaluate and select areas that are essential to the conservation of the species and that may require special management actions. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Vina Plains Unit, Butte and Tehema Counties (20,546 ha (50,769 ac))

This unit is proposed as critical habitat for Conservancy fairy shrimp because it contains occurrences of the species (CNDDB 2002) within vernal pools found on Anita clay and Tuscan loam soils (EPA 1994, Holland 1998, Tehama County 1999, USDA 2001). These soils support pool types that remain inundated for sufficient periods of time to allow Conservancy fairy shrimp to hatch, mature, and reproduce, but do not contain water during the summer preventing the invasion of predator species such as bullfrogs and fish. This unit represents the northern extent of Conservancy fairy shrimp range.

Conservancy fairy shrimp in this area occupy vernal pools that are classified as Northern Hardpan by Sawyer and Keeler-Wolf (1995) and occur on the Tuscan, Red Bluff, and Riverbank geologic formations. Within this unit vernal pools occur in complexes with a range of pool sizes, from over several acres to less than a tenth of an acre, in areas of hummocky ground on old terraces above recent river flood plains below the foothills (Alexander and Schlising 1997, Keeler-Wolf et al. 1998). The boundaries of this unit were delineated to include the interconnected pools, swales, and interconnected uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where Conservancy fairy shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Conservancy fairy shrimp hatching, growth and reproduction, and dispersal, but not necessarily every year.

This unit includes relatively undisturbed, hydrologically intact vernal pool habitats, that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for Conservancy fairy shrimp. This area also provides seasonal habitat for waterfowl and other migratory bird species which aid in the dispersal of Conservancy fairy shrimp among vernal pools within the unit, and between other habitats across the species range.

The majority of the lands included within this unit are privately owned. This unit contains TNC's Vina Plains preserve as well as other TNC lands 2,264 ha (5,660 ac) and conservation easements 4,348 ha (10,870 ac). The NRCS also holds WRP conservation easements or agreements on 57 ha (142 ac). The preserve contains over 300 species of plants, and diverse communities of aquatic invertebrates. Since the 1960's, the Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating of the effects of grazing and fire on vernal pool plants, animals, and ecosystems (Griggs 2000). Much of the basic life history information known about vernal pool crustaceans was collected at Vina Plains (e.g. Lanway 1974, Ahl 1991, Syrdahl 1993, Gallagher 1996). The results of this research have provided crucial information to guide management and monitoring of vernal pool ecosystems and to identify factors which influence population dynamics of a number of endangered species, including Conservancy fairy shrimp. The Vina Plains is open to the public and provides excellent outreach and educational opportunities. In addition to TNC, the importance of vernal pool habitats in this area has been recognized by the CDFG, the Service, the EPA, the CNPS, the NRCS's WRP, and by researchers at the CSU at Chico, who have all supported research and conservation efforts for Conservancy fairy shrimp and other vernal pool species within this unit. Urban development north of Chico and the conversion of grazed lands to more intensive agricultural uses threaten vernal pool habitat within this unit.

The Vina Plains Unit extends from south of Deer Creek to north of Rock Creek and the Chico Airport near the City of Chico. State Highway 99 bisects this unit. The western boundary generally parallels the Southern Pacific Railway line. The eastern boundary of this unit extends to the boundary of the East Red Bluff watershed. This unit overlaps Unit 7 for vernal pool fairy shrimp and Unit 3 for vernal pool tadpole shrimp and contains part of Unit 1 for hairy Orcutt grass, Unit 2 for Greene's tuctoria, Unit 1 for Hoover's spurge, and Unit 4 for slender Orcutt grass. Additional sensitive species occurring in this unit include California linderiella and Bogg's Lake hedge-hyssop.

Unit 2, Colusa Unit, Sacramento Valley, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical habitat for Conservancy fairy shrimp because it contains occurrences of the species within large, alkaline vernal pools formed on the Modesto geologic formation on Willows and Riz soils that provide the primary constituent elements essential to the conservation of the Conservancy fairy shrimp (Holland 1998, Silveira 2000, CNDDB 2002). Conservancy fairy shrimp in this area occupy pools that are often large, shallow and alkaline. They may display white salt deposits following pool drying. These pool types remain inundated for sufficient periods of time to allow Conservancy fairy shrimp to hatch, mature, and reproduce, but do not contain water during the summer, preventing the invasion of predator species such as bullfrogs and fish. This area is important to maintain the diversity of habitats in which Conservancy fairy shrimp occur.

This unit is primarily located on the Sacramento National Wildlife Refuge (5,126 ha (12,816 ac)). Any additional lands within this unit are privately owned. The refuge supports over 355 native plant taxa, including a number of rare alkaline species (Oswald and Silveira 1995). Vernal pool habitats on the refuge are specifically managed for the conservation of listed species, and to promote habitat for migratory birds and waterfowl. As a result this unit also provides essential habitat for avian species that aid in the dispersal of Conservancy fairy shrimp and other vernal pool crustacean cysts. The Sacramento National Wildlife Refuge contains the only remnants of the widespread Colusa Plains vegetation that once covered the entire Colusa Basin (Silveira 2000). Vernal pool habitats within the area have become greatly fragmented and isolated from other habitats in the region.

The boundaries of this unit were delineated to include the interconnected pools, swales, and interconnected uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where Conservancy fairy shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Conservancy fairy shrimp hatching, growth and reproduction, and dispersal, but not necessarily every year.

This unit occupies vernal pool habitat east of Interstate 5 to the Colusa Trough from Riz Road on the north and Delevan Road on the south. This unit coincides with vernal pool fairy shrimp Unit 10, vernal pool tadpole shrimp Unit 5, Unit 3 for hairy Orcutt grass, and Unit 3 for Hoover's spurge. Other rare vernal pool species found in this unit include pappose spikeweed, Fremont's goldfields, alkali goldfields, Scribe's popcorn flower, Hoover's downingia, folded downingia, Heckard's peppergrass, heartscale, brittlescale, San Joaquin spearscale, Ferris' milk-vetch, spike-primrose, sessile mousetail, and the federally listed as endangered palmate-bracted bird's beak.

Unit 3, Jepson Prairie Unit, Solano County (9,927 ha (24,529 ac))

This unit is proposed as critical habitat for Conservancy fairy shrimp because it includes numerous occurrences of the species within one of the most pristine, intact vernal pool ecosystems remaining in California (Holland 1998, Solano County 1999, Solano County Farmland and Open Space 2001, CNDDB 2002). The unit boundary was drawn to include the vernal pools where Conservancy fairy shrimp occur, including the 32 ha (80 ac) Olcott Lake and other large playa pools associated with Solano Loam and Pescadero soil series. Conservancy fairy shrimp in this unit occupy vernal pool complexes extending from Jepson Prairie west towards the City of Fairfield. Within these complexes larger pools often occur with smaller pools and hogwallow depressions. Together the pools, swales, and associated uplands maintain the necessary timing and frequency of inundation for Conservancy fairy shrimp hatching, growth, and reproduction, but are dry during the summer. The relatively undisturbed, hydrologically intact condition of the Jepson Prairie increases the likelihood that it will continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for Conservancy fairy shrimp. This unit also provides habitat for avian species that aid in the dispersal of Conservancy fairy shrimp and other vernal pool crustacean cysts.

In addition to Conservancy fairy shrimp, the greater Jepson Prairie grassland area supports a diverse community of native plants and animals, including the only known occurrence of Delta green ground beetle, and occurrences of Solano grass, Colusa grass, California tiger salamander, vernal pool tadpole shrimp, vernal pool fairy shrimp, alkali milk-vetch, Bogg's Lake hedge-hyssop, legenere, California linderiella, and midvalley fairy shrimp. The southwestern portion of this unit contains vernal pool habitats near the Potrero Hills south of Travis Air Force Base. These vernal pool habitats occur in close proximity to tidal marshes and contain habitat for Contra Costa goldfields.

This unit includes the Jepson Prairie Preserve, jointly managed by the Solano County Farmlands and Open Space Foundation and the UC Reserve System. Jepson Prairie has long been recognized as an outstanding example of vernal pool ecosystems. In 1987 NPS named Jepson Prairie a National Natural Landmark, a designation given to sites that provide high quality habitat for threatened or endangered species. Jepson Prairie is the target of ongoing conservation planning efforts and active management. As part of the UC Reserve System, this area provides critical research opportunities for scientists to study Conservancy fairy shrimp, and to determine their response to different management regimes. Conducting this research is essential to ensure the conservation of Conservancy fairy shrimp and other vernal pool species. This unit also contains land owned by the CDFG (319 ha (797 ac)), and State Land Commission (7 ha (17 ac)), as well as conservation easements held by TNC (623 ha (1,090)) and by NRCS under the WRP program (436 ha (1,090 ac). The unit also includes portions of Travis Air Force Base (DOD lands totaling 238 ha (596 ac)). Within the greater Jepson Prairie grassland area, existing vernal pools are threatened by agricultural conversion, landfill expansion, power plant construction, and utility maintenance. Urbanization in the vicinity of Fairfield and Suisun, and landfill expansion projects in the vicinity of the Protero Hills, threaten vernal pool habitats in the area.

This unit occurs in the southern portion of Solano County, east and south of the City of Fairfield, south and southwest of the City of Dixon, and north of Nurse Slough and the confluence of the Sacramento and San Joaquin rivers. This unit contains Unit 3 for Colusa grass, Unit 2 for Solano grass, and overlaps with Unit 4 for Contra Costa goldfields. This unit is encompassed by Unit 11 for vernal pool tadpole shrimp and Unit 16 for vernal pool fairy shrimp.

Unit 4, Montezuma Unit, Solano County (603 ha (1,490 ac))

This unit is proposed as critical habitat for Conservancy fairy shrimp because it contains vernal pools that support the necessary timing, frequency, and duration of inundation essential for Conservancy fairy shrimp feeding, sheltering, reproducing, and dispersing (Lipton in litt. 2002, Levine Fricke Restoration Corp 2000). This is the most recently discovered occurrence of Conservancy fairy shrimp, and one of the only areas where this species occurs in the saline-alkaline transition zone between vernal pools and tidal marshes.

Most of the habitats within this unit are on private land, although portions of the Hill Slough Wildlife Area managed by the CDFG are also included within this unit. The primary threats to vernal pool habitats within this unit are alterations to hydrology from filling, diking, and dredging activities which may occur in the tidal marsh. This unit is also proposed so that special management actions may be taken to prevent the degradation of Conservancy fairy shrimp occurrences through alteration of the hydrology of their vernal pool habitats.

This unit is located near the Suisun Marsh in southern Solano County, east of Montezuma Slough and west of Collinsville Road; the northernmost portion of this unit is bisected by Birds Landings Road. Portions of this unit coincide with Unit 12 for vernal pool tadpole shrimp. In addition to Conservancy fairy shrimp, this unit contains occurrences of other rare vernal pool species including vernal pool fairy shrimp, alkali milk-vetch and dwarf downingia.

Unit 5, Northern San Joaquin Valley Unit, Stanislaus County (302 ha (746 ac))

This unit is proposed as critical habitat for Conservancy fairy shrimp because it contains the species within alkali sink vernal pools formed on Fresno series soils (CNDDB 2002). The unit boundary was designated to include the vernal pool complex mapped by Holland (1998) that maintains the necessary timing and frequency of inundation for Conservancy fairy shrimp hatching, growth, and reproduction, but is dry in the summer. The minimum mapping unit of Holland (1998) of 16 ha (40 ac) did not allow us to exclude all non-vernal pool areas from within the unit boundary. However, the entire unit is located within the San Joaquin River National Wildlife Refuge and restoration is currently the focus of conservation planning efforts by the Service. Additional restoration designed to enhance habitat for riparian species, as well as migratory birds and waterfowl, is also currently underway. This unit is proposed so that special management actions, including appropriate wetland management, can be taken to maintain the natural hydrology of the vernal pools where Conservancy fairy shrimp are known to occur. This unit is over 70 km (43 mi) from the nearest unit to the south and over 40 km (25 mi) from the nearest unit to the north. Such isolated populations may have genetic characteristics essential to overall long-term conservation of the species (i.e. they may be genetically different than more central populations) (Lesica and Allendorf 1995, Fugate 1998).

Lands within this unit form a mosaic of riparian habitat, wetlands, and grasslands. The San Joaquin River National Wildlife Refuge is the primary wintering site of 98 percent of the Aleutian Canada geese that winter in the Valley (October—April), and it is a major wintering and migration area for lesser and greater sandhill cranes, cackling Canada geese, and white-fronted geese. These migratory birds act as dispersal agents for Conservancy fairy shrimp and other vernal pool crustacean species.

This unit is situated west of the City of Modesto and east of the confluence of the San Joaquin and Stanislaus rivers. Caswell Memorial State Park lies just north of this unit. This unit is bisected by the Hetch Hetchy Aqueduct and State Highway 132. This unit overlaps vernal pool fairy shrimp Unit 20. It is also contains California linderiella and California tiger salamander occurrences, in addition to a number of rare non-vernal pool species including the federally listed endangered riparian wood rat and riparian brush rabbit.

Unit 6, Merced Unit, Merced and Mariposa Counties (63,750 ha (157,525 ac)

This unit is proposed as critical habitat for Conservancy fairy shrimp because it contains occurrences of the species within large, playa vernal pools found on Raynor Cobbly clay soils on the Mehrten Formation (CNDDB 2001, EIP Associates 1999). These pool types provide the necessary length and timing of inundation essential for the conservation of Conservancy fairy shrimp. The Merced Unit encompasses the largest block of pristine, high density vernal pool grasslands remaining in California (Vollmar 1999). The relatively undisturbed, hydrologically intact condition of the unit increases the likelihood that it will continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for Conservancy fairy shrimp. Genetic analyses of vernal pool tadpole shrimp revealed that occurrences in this unit were genetically different from other occurrences in California, and that this area was isolated from other vernal pool habitats (King 1996). Given that Conservation fairy shrimp and vernal pool tadpole shrimp are dispersed in similar ways, it is reasonable to assume that Conservancy fairy shrimp occurrences in this areas are also isolated from other occurrences throughout its range, and may also have unique genetic characteristics.

Vernal pool habitats in eastern Merced County are seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced campus and associated development. Effects associated with the UC campus and associated community could result in loss and degradation of vernal pool habitats within this unit. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Merced County and the CDFG are currently gathering data on presence, distribution, and microhabitat preferences of vernal pool crustaceans to aid in developing long-term conservation planning strategies for eastern Merced County. There is interest among ranch owners to establish conservation easements that will support rangeland and vernal pool conservation. The Conservancy fairy shrimp occurrence at the Flying M Ranch is already being managed through a conservation easement with TNC that conserves over 2,023 ha (5,000 ac) of vernal pool and upland habitat. Land ownership within the unit includes approximately 419 ha (1,048 ac) of DOD, (3 ha (8 ac) of BLM, and 10 ha (26 ac) of California State Parks. TNC has a total of 4,513 ha (11,283 ac) of conservation easements within this unit.

A majority of the vernal pool habitat in the Merced Unit is in eastern Merced County. The eastern edge of the unit overlaps into western Mariposa County and in the south it extends to Deadman Creek. The northern boundary parallels the Merced River. The unit is located east of Highway 99 and the City of Merced, Planada, and Le Grand. The eastern boundary extends into the low elevation foothills of the Sierra Nevada. The boundaries of this unit overlap with San Joaquin Valley Orcutt grass Units 2 and 3, Colusa grass Units 7, Greene's tuctoria Unit 6, succulent owl's-clover Units 3B, vernal pool fairy shrimp Unit 22, and vernal pool tadpole shrimp Unit 15. Other sensitive vernal pool species found within this unit include California tiger salamander, shining navarretia, dwarf downingia, Bogg's Lake hedge-hyssop, western spadefoot toad, and California linderiella.

Unit 7, Grassland Ecological Unit, Madera, Merced and Stanislaus Counties (46,142 ha (114,016 ac))

We propose this area as critical habitat for Conservancy fairy shrimp because it supports multiple occurrences of the species within large, playa vernal pools of the Edminstor and Kesterson soil series (Holland 1998, USDA 2001, CNDDB 2002). The unit boundary was drawn to include Conservancy fairy shrimp and the vernal pool complexes mapped by Holland (1998) where the species is known to occur. These features maintain the necessary length and timing of inundation for Conservancy fairy shrimp hatching, maturation, and reproduction, but are dry in the summer and do not support aquatic species such as fish or bullfrogs. Conservancy fairy shrimp are found in large numbers throughout this unit, making this area a potential source for propagules dispersing to Conservancy fairy shrimp habitats to the south in Ventura County, to the east in eastern Merced County, and to the north in Stanislaus County. This unit is also proposed as critical to ensure that special management actions are taken to prevent or reverse changes in hydrology, contamination from adjacent land use, and invasion by aquatic species that threaten Conservancy fairy shrimp occurrences within this unit.

This area contains the largest intact vernal pool habitat for Conservancy fairy shrimp in the San Joaquin Valley (Holland 1998). This unit also provides essential habitat for migratory waterfowl that aid in the dispersal of Conservancy fairy shrimp and other vernal pool crustacean cysts. The Grassland Ecological Unit includes Kesterson, San Luis, and Merced National Wildlife Refuges (12,765 ha (31, 542 ac)), CDFG lands (1,703 ha (4,257 ac)), CDFG administration lands (1,052 ha (2,631 ac)), California State Parks (1,358 ha (3,394 ac)), and private lands protected by WRP easements or agreements (54 ha (134 ac)). Combined, these lands are known as the Grasslands Ecological Area, a 66,773 ha (160,000 ac) area which supports the largest remaining areas of several rare valley floor habitats within the San Joaquin valley, including examples of alkali grasslands, alkali scrublands, wild rye grasslands, cotton wood riparian forests, vernal marshes, relict dune lands, and high quality vernal pool habitats.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit represents Unit 23 for vernal pool fairy shrimp and Unit 16 for vernal pool tadpole shrimp. The western half of this unit represents Unit 2 for longhorn fairy shrimp and the eastern half represents Unit 8 for Colusa grass, and Unit 6 for Hoover's spurge. In addition to the species mentioned above, vernal pool smallscale, alkali milk-vetch, western spadefoot toad, and California linderiella are present within this unit as well.

Unit 8, Ventura County Unit, Ventura, Santa Barbara, and Los Angeles Counties (18,831 ha (46,531 ac))

The Ventura County unit consists of one area in the north-central portion of Ventura County. Vernal pool fairy shrimp and Conservancy fairy shrimp are known to co-occur at relatively high elevation (~1,700 m (5,500 ft)) forested sites within the Los Padres National Forest. All of this unit is owned by the USFS. Almost all of the known localities that possess these two species within the state of California exist at much lower elevations in grassland habitats. The map polygon perimeter consists of an area that is known to contain vernal pool and Conservancy fairy shrimp occurrences and isolated pools that provide habitat for the two species. The Ventura County unit is essential for the conservation of Conservancy fairy shrimp because it contains high elevation (~ 1,700 m (5,500 ft)) ephemeral aquatic environments that are rarely associated with fairy shrimp. The Ventura County sites that are occupied by Conservancy fairy shrimp are 124 km (200 m) from other species occurrences in the Great Central Valley, thereby suggesting that the Ventura County population(s) is geographically isolated from the population(s) that occur farther east and north. Such isolated and peripheral populations may have genetic characteristics that are different than more central populations, and may be important for conservation (Lesica and Allendorf 1995, Fugate 1998).

Longhorn Fairy Shrimp Criteria

In proposing critical habitat units for longhorn fairy shrimp we evaluated the life history and current distribution of the species described in the background section of this rule, the primary constituent elements described in the primary constituent element section of this rule, and the threats to the species described under vernal pool crustaceans above and additional threats described below. This information allowed us to determine which areas are likely to be essential to the conservation of these species.

Longhorn fairy shrimp are currently known from three locations, Altamont Pass area at the Contra Costa and Alameda county line, San Luis National Wildlife Refuge Complex in western Merced County, and the Soda Lake area in San Luis Obispo County. Longhorn fairy shrimp near Soda Lake occur both on protected land within the Carrizo National Monument, and on private land. The occurrences on private land are threatened by proposed development of ranchettes, production of animals used in biotechnology industries, and road construction. Longhorn fairy shrimp occurrences in the Altamont Pass area in Contra Costa and Alameda counties have been heavily impacted by wind energy development, although some of these occurrences are currently protected from development on land owned by the East Bay Regional Parks District (EBRPD) (Eng et al. 1990, EBRPD 2001). Longhorn fairy shrimp are protected from development on the Kesterson National Wildlife Refuge in Merced County, however, these occurrences are threatened by wetland management practices that have led to prolonged inundation of longhorn fairy shrimp habitats and inadvertent introduction of fish and bullfrogs (CNDDB 2001).

In areas where longhorn fairy shrimp habitats have been protected, the species may be still be threatened if adequate monitoring and management is not conducted. Management and monitoring are necessary to recognize and protect populations from indirect effects, such as changes in hydrology, contamination, siltation, erosion, competition with non-native species, and human-related disturbance, such as off road vehicle use.

Longhorn Fairy Shrimp Unit Review

We conducted a review of the currently known range of longhorn fairy shrimp to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the presence of the species and the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Altamont Hills Unit A and B, Contra Costa and Alameda Counties (322 ha (795 ac))

This unit is proposed as critical habitat for longhorn fairy shrimp because it supports occurrences of the species within clear depression pools in sandstone outcrops (Eriksen and Belk 1999, EBRPD 2001, CNDDB 2002). These pool types become inundated during winter rains and hold water for sufficient lengths of time necessary for longhorn fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, but are dry during the summer and do not necessarily fill with water every year; This is an unique habitat for longhorn fairy shrimp, and helps to maintain a diversity of habitats for the species. The Altamont Hills Unit is an important area for longhorn fairy shrimp because it represents the northern limit of the species range, and is one of only 3 locations where the species is known to occur throughout their entire range. Longhorn fairy shrimp in the Altamont Hills Unit are located about 100 km (60 mi) northwest of the next known occurrence at Kesterson National Wildlife Refuge in Merced County (Eriksen and Belk 1999). It is likely these occurrences have genetic characteristics that differ from other occurrences in other portions of the species range, and these characteristics may be important for the conservation of longhorn fairy shrimp (Fugate 1992, 1998). Each of these locations reduces the probability that a chance event would result in the extinction of the species.

This unit is located primarily on EBRPD and Contra Costa Water District land. This unit is located in Altamont Hills north and northeast of the City of Livermore, and consists of two subunits, both near the Contra Costa and Alameda county line. Subunit A is located in Contra Costa County directly north of the Alameda County line near the Vasco Caves. Subunit B is located directly in Alameda County just south of the Contra Costa County line in the vicinity of Brushy Peak. A large number of federally listed and sensitive species are found within this area, including the California red legged frog, San Joaquin kit fox, California tiger salamander and California linderiella.

Unit 2, Grassland Ecological Unit, Madera, Merced and Stanislaus Counties (29,817 ha (73,677 ac))

This unit is proposed as critical habitat for longhorn fairy shrimp because it contains turbid alkaline vernal pools on Edminster loam and Turlock sandy loam that support occurrences of the species (USDA 2001, Holland 1998, CNDDB 2002). This is the only location where longhorn fairy shrimp occur in the Central Valley of California. Longhorn fairy shrimp within this unit are threatened by altered hydrology and invasion of aquatic predators. This unit is also designated so that special management actions can be taken to maintain the appropriate timing, frequency, and duration of inundation of longhorn fairy shrimp habitat essential to the conservation of longhorn fairy shrimp within managed wetland areas.

This unit is over 209 km (130 mi) from the longhorn fairy shrimp occurrence to the south, and over 80 km (50 mi) from longhorn fairy shrimp occurrences to the north. This occurrence is likely genetically different from the two other occurrences (Fugate 1992, 1998). Longhorn fairy shrimp are known from only 3 locations, and each of these locations is important to the conservation of this species by providing a buffer against catastrophic or stochastic events which could extirpate any one occurrence and seriously reduce the likelihood of survival and recovery of the species as a whole.

This unit includes natural habitats within the San Joaquin River watershed. The Grassland Ecological Unit includes Kesterson, San Luis, and Merced National Wildlife Refuges (9,303 ha (23, 258 ac)), CDFG lands (1,703 ha (4,257 ac)), CDFG administration lands (1,052 ha (2,631 ac)), California State Parks (1,358 ha (3,394 ac)), private lands protected by WRP easements or agreements (54 ha (134 ac)), and numerous other Federal and private conservation easements. Combined, these lands are known as the Grasslands Ecological Area, a 66,773 ha (160,000 ac) area which supports the largest remaining areas of several rare valley floor habitats within the San Joaquin valley, including examples of alkali grasslands, alkali scrub lands, wild rye grasslands, cotton wood riparian forests, vernal marshes, relict dune lands, and high quality vernal pool habitats. Threats to vernal pool habitats in this unit include agricultural conversion, changes in hydrology, contamination from adjacent land use, and invasion by aggressive plants.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit overlaps Unit 23 for vernal pool fairy shrimp, Unit 16 for vernal pool tadpole shrimp, and Unit 7 for Conservancy fairy shrimp. In addition to the species mentioned above, vernal pool smallscale, Alkali milk-vetch, western spadefoot toad, and California linderiella are present within this unit as well.

Unit 3, Carrizo Plain Unit, San Luis Obispo, Kern, and Monterey Counties (10,466 ha (25,862 ac))

This unit is proposed as critical habitat for longhorn fairy shrimp because it contains occurrences of the species living within Northern Claypan type vernal pools as described by Sawyer and Keeler-Wolf (1995) (CNDDB 2001). Longhorn fairy shrimp in the Carrizo Unit are found in shallow alkaline vernal pools within a Valley Saltbush Scrub matrix adjacent to the 1214 ha (3,000 ac) Soda Lake, the largest alkali wetland in central and southern California, which provides a winter haven for thousands of migratory birds.

The Carrizo Plain Unit represents the southern extent of the range of longhorn fairy shrimp. Longhorn fairy shrimp in the Carrizo Plain Unit are located 235 km (146 mi) southeast of the closest known occurrences at Kesterson National Wildlife Refuge in Merced County (Eriksen and Belk 1999). Such isolated populations may have genetic characteristics essential to overall long-term conservation of the species (Fugate 1998). The Carrizo Plain contains examples of native bunch grass, needle grass, and blue grass grasslands, as well as populations of federally listed San Joaquin kit fox, blunt nosed leopard lizard, giant kangaroo rat, California jewel flower, Lost Hills salt brush, Kern mallow and San Joaquin wooly threads (The Nature Conservancy 2001). North of the Carrizo Plain, vernal pools that occur along the San Andreas fault are small sag pond types surrounded by annual grassland or Interior Coast Range Saltbush Scrub (Keeler-Wolf et al. 1998). The Carrizo Plain Unit contains portions of the Carrizo Plain National Monument administered by the BLM, TNC, and the CDFG. The BLM lands within the unit total approximately 6,220 ha (15,549 ac) and the CDFG lands total approximately 93 ha (233 ac). Other vernal pool habitats in the unit are located on private land.

This unit is located in the vicinity of California Valley and Soda Lake. State Highway 58 is located north of the unit. Most of the habitat is east of Soda Lake Road, however, Soda Lake Road crosses through the western edge of the unit in several areas. To the east, the unit is bordered by the San Andreas Rift Zone. This unit coincides with vernal pool fairy shrimp Unit 25.

Vernal Pool Fairy Shrimp Criteria

In proposing critical habitat units for vernal pool fairy shrimp we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of vernal pool fairy shrimp and to delineate units so that threats to these species might be minimized.

The historic range of vernal pool fairy shrimp extended throughout the low and mid-elevation regions of the Central Valley into southern and coastal California and southern Oregon Agate Desert. Vernal pool fairy shrimp have been extirpated from a number of their historic occurrences as a result of urban development and conversion to agriculture. Rapid urbanization in Placer, Sacramento, and Tehama counties, California, has accounted for the majority of recent vernal pool fairy shrimp extirpations, although conversion to agriculture in San Joaquin, Merced, and other counties also has contributed to the continued decline of this species.

Remaining vernal pool fairy shrimp occurrences continue to be threatened by all of the factors that historically led to the decline of this species. CNDDB (2001) estimates that 34 percent of the remaining occurrences of this species are threatened by development and agricultural conversion. Another 15 percent are threatened by military activities (CNDDB 2001). An additional 15 percent are threatened by operations and maintenance activities within utility and transportation right-of-ways, including grading, discing, and trenching activities which destroy the topographical features necessary for vernal pool habitats to support occurrences of vernal pool fairy shrimp (CNDDB 2001). Pesticide and herbicide use within utility easements also threaten many occurrences of vernal pool fairy shrimp (CNDDB 2001). Other vernal pool fairy shrimp occurrences are threatened by off road vehicle use, logging, mining, vandalism, dumping, and expansion of landfills (CNDDB 2001).

Numerous occurrences of vernal pool fairy shrimp are threatened by altered hydrology. In some cases vernal pools have been altered so that they contain water year round, allowing predators such as bullfrogs and fish to colonize vernal pool habitats (CNDDB 2001). In other cases artificial run off has resulted in the delivery of materials that destroy vernal pool water quality, including sediment from cement plants, pesticides from vineyards and other irrigated agricultural lands, pesticides from golf courses, and sediment from surrounding developments (CNDDB 2001).

Vernal Pool Fairy Shrimp Unit Review

We conducted a regional review across the range of vernal pool fairy shrimp to evaluate and select vernal pool habitats that are essential to the conservation of the species and that require special management. Important factors we considered were the known presence of vernal pool fairy shrimp and the presence of vernal pools and vernal pool complexes supporting the hydrological characteristics necessary to provide the primary constituent elements essential to the conservation of the species.

We identified areas that support high numbers of vernal pool fairy shrimp occurrences identified by CNDDB (2002) within vernal pool complexes containing the primary constituent elements for the species mapped by Holland (1998) and a number of other sources throughout the range of the species. We have identified areas necessary to conserve the species by maintaining a portion of the species current range and distribution and including some of the different kinds of habitats in which the species is known to occur. However, as is the case with all critical habitat designations, areas outside of this designation may still prove to be necessary to the recovery of this species. A description of each area is outlined below.

Oregon

Vernal pool fairy shrimp are the only species addressed in this proposed rule that occur in Oregon. Four units in Oregon are proposed as essential to the conservation of vernal pool fairy shrimp. The Oregon units occur approximately 200 km (125 mi) north of the nearest unit proposed for this species in California.

Unit 1A, B, C ,D, E, F, and G, North Agate Desert Unit, Jackson County (862 ha (2,130 ac))

This unit consists of seven subunits, all located to the north of Little Butte Creek. Three of the subunits are west of the Rogue River, and the remaining four are to the east. All but one of these subunits are located to the south of U.S. Route 234 (Sam's Valley Highway). The one remaining unit is located to the east of the Rogue River, about 2.4 km (1.5 mi) north of the confluence with Reese Creek. This unit represents the northern limit of the species' distribution and therefore may contribute significantly to the species' genetic diversity (Lesica and Allendorf 1995). It is of sufficient size to sustain the natural ecosystem processes (e.g., fires) that have historically influenced vernal pool habitat and is disjunct from the nearest other unit proposed for Oregon, Unit 4, by over 3.2 km (2 mi).

Unit 2A, B, C, D, and E, White City East Unit, Jackson County (911 ha (2,251 ac))

This unit consists of five subunits, located east of U.S. Route 62 (Crater Lake Highway) and south and southeast of Dutton Road. The largest and easternmost of the subunits occurs just to the east and north of Agate Lake. This unit provides the easternmost extent of the species' range in Oregon. It represents a significant component of the species' original range in the state and is of a sufficient size to sustain the natural ecosystem processes (e.g., fires) that have historically influenced vernal pool habitat. It is disjunct by more than 1.6 km (1 mi) from Unit 3, White City West, and by approximately 5.6 km (3.5 mi) from the North Agate Desert Unit.

Unit 3A, B, and C, White City West Unit, Jackson County (931 ha (2,301 ac))

This unit consists of three subunits, located west of Agate Road, south of the Rogue River, and east of Bear Creek. This unit contains the best remaining examples of the original Agate Desert mounded prairie habitat. It is of sufficient size to sustain the natural ecosystem processes (e.g., fires) that have historically influenced vernal pool habitat; it is disjunct from the White City East Unit by more than 1.6 km (1 mi) and from the Table Rocks Unit by over 2.4 km (1.5 mi).

We believe that, taken together, the proposed Agate Desert units (Units 1-3) comprise a functional vernal pool complex consisting of vernal pools, mounded prairie and associated uplands, where natural processes, including connectivity, function within or near the natural range of variability. Each of the three proposed Agate Desert units is essential to the conservation of vernal pool fairy shrimp populations in the Agate Desert.

Unit 4A and B, Table Rocks Unit, Jackson County (361 ha (892 ac))

This unit consists of two subunits, located on two flat-topped mesas known as Upper and Lower Table Rocks, situated north and west of the Rogue River. These rimrock features are remnants of ancient lava flows that filled portions of the Rogue River nearly 10 million years ago (Bureau of Land Management (BLM) 1998). Subsequent erosion of softer geologic layers has left these harder, andesite (volcanic rock) formations rising some 245 m (800 ft) above the present Rogue Valley. Vernal pools on the Table Rocks differ from those of the Agate Desert, in that they are formed over an impervious layer of bedrock. This unit represents a unique habitat for vernal pool fairy shrimp in Oregon; Table Rocks fairy shrimp populations differ ecologically from fairy shrimp populations in the Agate Desert. The Table Rocks Unit is disjunct from the North Agate Desert Unit by over 3.2 km (2 mi), and from the White City West Unit by approximately 2.4 km (1.5 mi).

California

Unit 5, Redding Unit, Shasta County (1,849 ha (4,569 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains the largest intact vernal pool habitat in the northern portion of vernal pool fairy shrimp's range in California. Occurrences of the species (CNDDB 2002) within vernal pools mapped by Holland (1998) are found on old alluvial terraces above the Sacramento River and often on Redding and Corning soil complexes (Shasta County 2001). Generally these pools are small in size, although the Stillwater Plains area supports unique pools which are several acres in size. These vernal pools provide feeding and sheltering habitat for the species and remain inundated for sufficient lengths of time to allow vernal pool fairy shrimp to hatch, mature, and reproduce.

The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth, reproduction, and dispersal.

This unit supports systems of hydrologically interconnected pools and swales within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustaceans to complete their life-cycle.

This unit represents contains all of the primary constituent elements for the species and comprises the northern extent of the species range in California. Because occurrences within this unit are at the limit of the species range in California they may have genetic characteristics essential to overall long-term conservation of the species (i.e., they may be genetically different than more central populations) (Fugate 1992, 1998, Lesica and Allendorf 1995).

Most of the land included within this unit is privately owned. The BLM owns 17 ha (42 ac) within this unit and a further 52 ha (130 ac) is private land protected under conservation easement or agreement as part of the Wetlands Reserve Program (WRP). The Stillwater Plains Conservation Bank, specifically established to contribute to the recovery of vernal pool fairy shrimp, is located within this unit. The City of Redding and other local and state planning organizations are currently developing a HCP to provide for the conservation of vernal pool fairy shrimp. This unit would provide an area where conservation efforts for vernal pool fairy shrimp could take place.

This unit is located in the area east of the Redding Municipal Airport between Airport Road to the west and Deschutes Road to the east. The unit extends to Dersch Road in the south and towards Lassen Park Highway in the north. This unit comprises a portion of the Stillwater Plains. This unit overlaps slender Orcutt grass Unit 2B and vernal pool tadpole shrimp Unit 1. Other sensitive species occurring within this unit include Red Bluff dwarf rush (Juncus leiospermus var. leiospermus), California linderiella (Linderiella occidentalis), Henderson's bent grass (Agrostis hendersonii), and four angled spike rush (Eleocharis quadrangulata).

Unit 6, Red Bluff Unit, Tehama County (18,562 ha (45,865 ac)

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains the species (CNDDB 2002) within vernal pools mapped by Holland (1998) and the pools contain water for sufficient periods of time necessary for vernal pool fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering. Vernal pool fairy shrimp within this unit occur within vernal pools formed on alluvial terraces west of the Sacramento River and associated with Newville/Corning and Redding/Corning soil complexes (USDA 2001) exhibiting well developed mima mound topography. The vernal pools within this unit are generally small and may not be inundated long enough to support other longer-lived vernal pool species.

The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth, reproduction, and dispersal. This unit contains several large (i.e., over (4,068 ha) 10,000 ac) vernal pool habitat complexes. These areas are relatively undisturbed, hydrologically intact vernal pool habitats that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. This unit also provides essential habitat for migratory waterfowl that aid in the dispersal of vernal fairy shrimp and other vernal pool crustacean cysts.

The majority of the lands included within this unit are privately owned. The CDFG owns 175 ha (433 ac) within this unit. Urban expansion from the city of Red Bluff, and agricultural conversion in other portions of the unit, threaten existing vernal pool fairy shrimp habitats throughout this unit. However, this unit also contains large private conservation areas established specifically to contribute to the recovery of vernal pool fairy shrimp and compensate for the loss of vernal pool habitat, including the 2,023 ha (5,000 ac) Tehama Fiber Farm mitigation area. CDFG's Thomes Creek Ecological Reserve is also located within this unit.

This unit extends from southwest of Red Bluff at Red Bank Creek south to Thomes Creek. The eastern boundary includes the vernal pool habitat from the Southern Pacific Railroad near Coyote Creek south paralleling Interstate 5 to Thomes Creek. Other vernal pool species occurring within this unit include Boggs Lake hedge-hyssop (Gratiola heterosepela), Baker's navarretia (Navarretia leucocephala ssp. bakeri), Red Bluff dwarf rush, Douglas' pogogyne (Pogogyne douglasii), western spadefoot toad (Scaphiopus hammondi), legenere (Legenere limosa), California linderiella, Ahart's paronychia (Pyronychia ahartii), Henderson's bent grass, and dwarf downingia (Downingia pusilla).

Unit 7, Vina Plains Unit, Tehama, and Butte Counties (23,883 ha (59,015 ac))

This unit is proposed as critical habitat because it contains vernal pool fairy shrimp (CNDDB 2001) living within large vernal pool grassland areas that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units (EPA 1994, Holland 1998, Tehama County 1999). The boundaries of this unit were delineated to include the interconnected pools, swales, and uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp to complete their life-cycles.

The vernal pools within this unit contain water during the winter, and provide the necessary length and timing of inundation, water quality, and freedom from predation that allow vernal pool fairy shrimp to hatch, feed, reproduce, and shelter. Vernal pool fairy shrimp in this unit occur within Northern Volcanic Mudflow vernal pools, these pools are generally small and tend to be inundated for relatively short periods of time. Vernal pool fairy shrimp are also found within larger vernal pools forming on hardpans within this unit. These pools tend to be larger and longer lasting than Northern Volcanic Mudflow pools, and may also support occurrences of other, longer lived species such as Conservancy fairy shrimp.

The pool types within this unit maintain the diversity of habitats in which vernal pool fairy shrimp are known to occur and provide relatively undisturbed, hydrologically intact vernal pool habitats that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. This unit also provides habitat for migratory waterfowl that aid in the dispersal of vernal pool fairy shrimp and other vernal pool crustacean cysts.

The majority of the lands included within this unit are privately owned. This unit contains The Nature Conservancy's (TNC) Vina Plains preserve as well as other TNC lands 2,264 ha (5,660 ac) and conservation easements 4,348 ha (10,870 ac). Other ownership within this unit includes 57 ha (142 ac) of private land protected under conservation easement or agreement under the Natural Resource Conservation Services's (NRCS) Wetland Reserve Program (WRP). The Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating the effects of grazing and fire on vernal pool plants, animals, and ecosystems (Griggs 2000). Much of the basic life history information known about vernal pool crustaceans was collected at Vina Plains (e.g., Lanway 1974, Ahl 1991, Syrdahl 1993, Gallagher 1996). The importance of the Vina Plains area has been recognized by a number of state, local, and Federal agencies, and they have been the focus of several conservation planning efforts. TNC, CDFG, the Service, the EPA, the CNPS, the NRCS WRP, and researchers from California State University (CSU) at Chico have all supported research and conservation efforts for vernal pool species within this unit.

This unit is located in the northeastern portion of the Sacramento Valley from Deer Creek in Tehama County to Chico in Butte County. The unit extends south and east of the Sacramento River paralleling the low elevation foothill region of the Sierra Nevada and represents the northeastern extent of vernal pool fairy shrimp's range in California. This unit coincides with Unit 3 for vernal pool tadpole shrimp, and incorporates Unit 1 for Conservancy fairy shrimp, Unit 4 for slender Orcutt grass, Unit 2 for Greene's tuctoria, Unit 1 for hairy Orcutt grass, Unit 1 for Hoover's spurge, and Units 1 and 2 for Butte County meadowfoam. Other vernal pool species occurring within this unit include Boggs Lake hedge-hyssop, Red Bluff dwarf rush, Douglas' pogogyne, western spadefoot toad, legenere, California linderiella, California tiger salamander (Ambystoma californiense), Ahart's paronychia, Henderson's bent grass, Sanford's arrowhead (Sagittaria sanfordii), and dwarf downingia.

Unit 8, Orland Unit, Tehama County (5,760 ha (14,233 ac)

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains occurrences of the species and vernal pools, swales, and associated uplands that support vernal pool fairy shrimp (Holland 1998, Tehama County 2001, CNDDB 2002). Vernal pool fairy shrimp in this unit are found in vernal pools formed on alluvial terraces west of the Sacramento River and associated with Anita clay and Tuscan loam soils (USDA 1994). These vernal pools are generally small, and exhibit well developed mima mound topography. They contain water for sufficient periods of time necessary for vernal pool fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth and reproduction, and dispersal, but not necessarily every year. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal.

This unit contains large vernal pool habitat areas in the northwestern portion of the range of vernal pool fairy shrimp. These areas provide relatively undisturbed, hydrologically intact vernal pool habitats that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. These vernal pool habitats support systems of hydrologically interconnected pools and swales within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes.

This unit extends from the Tehama/Glenn county border in the south, west of Ingrahm Road and east of the Black Butte Reservoir, to the vicinity of Rice Creek in the north. This unit also contains a Pacific Gas and Electric (PG&E) pipeline mitigation area established specifically for the conservation of vernal pool fairy shrimp. Other vernal pool species occurring within this unit include Baker's navarretia, western spadefoot toad, Ahart's paronychia, and dwarf downingia. All the lands within this unit are privately owned.

Unit 9, Oroville Unit, Butte County (1,456 ha (3,598 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it supports vernal pools, swales, and associated uplands mapped by Holland (1998) and by the EPA (1994) and contains vernal pool fairy shrimp (CNDDB 2001). Vernal pool fairy shrimp within this unit live within pools occurring primarily on the Tuscan geologic formation (Liss 2001, Keeler-Wolf et al. 1998), which are some of the few remaining examples of Northern Volcanic Mudflow vernal pools described by Sawyer and Keeler-Wolf (1995). Northern Volcanic Mudflow vernal pools are generally small and tend to be inundated for relatively short periods of time. These pool types are essential to maintain the diversity of habitats in which vernal pool fairy shrimp are known to occur. Vernal pool fairy shrimp are also found living in Northern Hardpan vernal pools within this unit. These pools tend to be larger and longer lasting than the Northern Volcanic Mudflow pools.

The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth, reproduction, and dispersal. The majority of the lands included within this unit are privately owned. This unit contains Service lands (76 ha (187 ac)) and 7 ha (17 ac) of CDFG administered land. This unit contains a few areas that have been preserved within the City of Chico. However, the amount of vernal pool habitat currently protected within the unit is very small. Urban expansion, particularly in the vicinity of Chico, is the greatest threat to existing vernal pool habitats throughout this unit.

This unit occupies an area from near Chico south to near the intersection of Highway 99 and State Route 149 in Butte County. The unit extends southeast of the Sacramento River paralleling the low elevation foothill region of the Sierra Nevada. This unit is part of Unit 4 for vernal pool tadpole shrimp, and incorporates Unit 3 for Greene's tuctoria, Unit 2 for hairy Orcutt grass, Unit 2 for Hoover's spurge, and Unit 3 for Butte County meadowfoam. Other vernal pool species occurring within this unit include Boggs Lake hedge-hyssop, Red Bluff dwarf rush, Douglas' pogogyne, western spadefoot toad, legenere, California linderiella, California tiger salamander, Ahart's paronychia, Henderson's bent grass, Sanford's arrowhead, and dwarf downingia.

Unit 10, Sacramento National Wildlife Refuge Unit, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains occurrences of the species (CNDDB 2002) within the vernal pools and swales mapped by Holland (1998). Vernal pool fairy shrimp in this unit live within Northern Claypan vernal pools, as defined by Sawyer and Keeler-Wolf (1995). These vernal pools are associated with alkaline soils, such as Willows and Riz soils series, and typically form alkali playas which are larger and contain a more diverse species composition than the hardpan pools further south (Keeler-Wolf et al. 1998). These pools are inundated for a sufficient period of time to support all of the life history requirements of vernal pool fairy shrimp. Vernal pools on the Sacramento National Wildlife Refuge Complex , are often large, shallow and alkaline (Silveira 2000). Vernal pool habitats on the refuge are specifically managed for the conservation of listed species, and to promote habitat for migratory birds and waterfowl.

The Sacramento National Wildlife Refuge contains the last remnants of the widespread Colusa Plains vegetation that once covered the entire Colusa Basin (Silveira 2000). Vernal pool habitats within the area have become greatly fragmented and isolated from other habitats in the region due to land conversion to agriculture. This unit is important to maintain opportunities for vernal pool fairy shrimp dispersal between units to the north, over 50 km (31 mi) distant, and those to the south, over 110 km (68 mi) distant. Without this unit, vernal pool fairy shrimp occurrences to the north and south would be more than 160 km (100 mi) distant from one another, a distance at which genetic evidence indicates they are effectively isolated (Fugate 1992, 1998).

The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) and identified by the Service (Silveira 2000) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth, reproduction, and dispersal.

This unit is primarily located on the Sacramento National Wildlife Refuge (5,126 ha (12,816 ac)). Any additional lands within this unit are privately owned. This unit overlaps with Unit 6 for Greene's tuctoria, Unit 3 for hairy Orcutt grass, Unit 3 for Hoover's spurge, and Unit 2 for Conservancy fairy shrimp. Other important vernal pool and associated upland species found in the unit include pappose spikeweed (Hemizonia parryi ssp. rudis), Fremont's goldfields (Lasthenia fremontii), alkali goldfields (Lasthenia platycarpha), Scribe's popcorn flower (Plagiobothrys scriptus), Hoover's downingia (Downingia bella), folded downingia (Downingia ornatissima var. ornatissima), Heckard's peppergrass (Lepidium latipes var. heckardii), heartscale (Atriplex cordulata), brittlescale (Atriplex depressa), San Joaquin spearscale (Atriplex joaquiniana), Ferris' milkvetch (Astragalus tender var. farrisiae), spike-primrose (Boisduvalia stricta), sessile mousetail (Myosurus sessilis), and palmate-bracted bird's beak (Cordylanthus palmatus).

Unit 11, Beale Unit, Yuba and Placer Counties (2,853 ha (7,049 ac))

We propose the Beale Unit as essential for the conservation of vernal pool fairy shrimp because it contains large, relatively undisturbed vernal pool grassland habitats and a diversity of vernal pool habitat types supporting vernal pool fairy shrimp (CNDDB 2001, Jones and Stokes 1997b, Jones and Stokes 2002, Platenkamp 1998). Vernal pool fairy shrimp within this unit are found throughout several large vernal pool complexes. These complexes occur on four major geologic formations: the Modesto Formation; the Riverbank Formation; the Laguna Formation; and the Mehrten Formation (Platenkamp 1998). These habitats provide the hydrological characteristics necessary for vernal pool fairy shrimp growth, reproduction, dispersal, and other primary constituent elements essential to the conservation of this species. Different geologic formations provide a diversity of habitats for vernal pool fairy shrimp primarily through their effects on pool size and depth (Platenkamp 1998, Helm 1998).

This unit contains DOD land (419 ha (1,048 ac)) at Beale Air Force Base and BLM (3 ha (8 ac)) lands. Other lands within this unit are located on private property, and are threatened by agricultural conversion, urban expansion, and the expansion of Highway 70 and other transportation projects planned in the region. This unit is found east of Yuba City and State Highway 65, generally south of Hammonton Road and north of South Beale Road and 6th Street. The unit includes the western portion of Beale Air Force Base, west of Erle Street and Doolittle Drive. Other rare vernal pool species found within this unit include vernal pool tadpole shrimp and California linderiella.

Unit 12, Western Placer County Unit (19,387 ha (47,905 ac))

The Western Placer Unit was identified as critical habitat for vernal pool fairy shrimp because it contains numerous occurrences of the species (CNDDB 2001). The unit boundary was drawn to include these occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and Glazner (2001) and as visible on SPOT imagery. These complexes form interconnected hydrologic units of pools, swales and uplands that together maintain the timing and duration of inundation necessary for vernal pool fairy shrimp to hatch, mature, and reproduce. Vernal pool fairy shrimp within this unit occur in both Northern Hardpan and Northern Volcanic Mudflow vernal pools as described by Sawyer and Keeler-Wolf (1995). This unit also supports vernal pool fairy shrimp found in vernal pools on Exchequer soils on the Mehrten geologic formation, a rare type of Northern Volcanic Mudflow vernal pool which has been reduced to only a few acres in extent. The pools are relatively short lived and do not provide habitat for most other species of fairy shrimp (CNDDB 2001).

This unit includes a large number of conservation areas established specifically to contribute to the recovery of vernal pool fairy shrimp partly established through conservation efforts under section 7 of the Act. These include the Ahart Preserve, one of the few remaining examples of Northern Volcanic Mudflow vernal pools in the region, as well as the Orchard Creek Conservation Bank. This conservation bank was established for the protection of vernal pool fairy shrimp and to compensate for the loss of thousands of acres of vernal pool grassland habitats throughout Placer and Sacramento counties. Additional smaller conservation areas in this unit are located within the cities of Lincoln and Roseville, and in Placer County. Approximately 20 percent of all mitigation areas established for the long-term protection of vernal pool fairy shrimp are found within this unit. Placer County is currently developing a HCP for the conservation of vernal pool fairy shrimp in this area. A WRP easement of 63 ha (157 ac) is within this unit.

The Western Placer Unit contains 70 percent of the remaining vernal pool habitats in Placer County. TNC identified this area as one of the outstanding vernal pool sites remaining in the Sacramento Valley. Vernal pool habitats within this unit are threatened by the development of large transportation projects, the development of a university and associated infrastructure, residential developments, gravel mining operations, and agricultural conversion in the western portion of Placer County.

This unit generally occurs in western Placer County immediately north of the Sacramento County line, north of the City of Roseville and the City of Rocklin. The northern boundary occurs just north of the City of Lincoln. This unit occurs mostly west of State Highway 65. This unit provides habitat for sensitive vernal pool species such as Bogg's Lake hedge-hyssop, Red Bluff dwarf rush, western spadefoot toad, legenere, California linderiella, Ahart's paronychia, and dwarf downingia. A number of riparian species are also found in this unit in the vernal pool grasslands that border Coon Creek.

Unit 13, Mather Unit, Sacramento County (14,866 ha (36,733 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains occurrences of the species and vernal pool habitats that sustain the necessary timing and length of inundation required for the species to hatch, mature, reproduce, disperse, and enter dormancy (Holland 1998, Sacramento County 1999, CNDDB 2001). Vernal pool fairy shrimp in this unit occur within a diversity of vernal pool habitats, including young or low terrace vernal pools on the Riverbank Formation, old or high terrace vernal pools on the Laguna and Arroyo Seco geologic formations, and Northern Volcanic Mudflow vernal pools on the Mehrten and Valley Springs geologic formations.

This unit includes several conservation areas established by private entities, including the Sunrise Douglas Conservation Bank, the Arroyo Seco Conservation Bank, the Churchill Downs mitigation area, and Teichert mitigation areas. These areas were established specifically to contribute to the conservation of vernal pool fairy shrimp, and represent compensation measures for the loss of thousands of acres of vernal pool fairy shrimp habitat within Sacramento County. The continued functioning of these areas is essential to the conservation of vernal pool fairy shrimp and other vernal pool species. The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth, reproduction, and dispersal.

This area supports a diversity of vernal pool species and habitats, and is the focus of numerous conservation planning efforts. This area has been identified by the Sacramento Valley Open Space Conservancy, the CNPS, and TNC as an excellent example of vernal pool grasslands, supporting a rich and diverse community of vernal pool endemic plants and animals within Sacramento County. This unit contains areas on private, county, and Federal land, including lands leased or owned by Sacramento County at Mather Regional Park, the former Mather Air Force Base, and at the county landfill. BLM owns 6 ha (18 ac) within this unit. Vernal pool habitats in this unit are threatened by urbanization from the expanding cities of Sacramento and Elk Grove. Conversion to intensive agriculture, particularly vineyards, is also a significant threat to vernal pool fairy shrimp in this unit.

This unit includes the area to the southeast of the City of Sacramento in Sacramento County, east of Highway 99 and south of Interstate 80. The unit is generally east of Bradshaw Road, northwest of Grant Line Road, west of Scott Road, and includes a portion of Mather Field. The unit is bisected by the Folsom South Canal. This unit also represents Unit 8 for vernal pool tadpole shrimp, and contains Unit 6 for slender Orcutt grass and Unit 2 for Sacramento Orcutt grass. In addition to these species, this unit contains occurrences of many other rare, endemic vernal pool species including midvalley fairy shrimp (Branchinecta mesovalliensis), Bogg's Lake hedge-hyssop, western spadefoot toad, legenere, California linderiella, and Ahart's paronychia.

Unit 14, Cosumnes Unit, Sacramento County (26,600 ha (65,728 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it supports the species (CNDDB 2001) and its habitat (Holland 1998, Sacramento County 1999). The unit boundary was drawn to include several large vernal pool complexes mapped by Holland (1998) and numerous individual vernal pools mapped by Sacramento County (1999) and visible on SPOT imagery. Together, these identified habitats represent some of the largest remaining vernal pool complexes in the Sacramento Valley that provide the necessary timing and duration of inundation for vernal pool fairy shrimp hatching, growth, and reproduction. Vernal pool fairy shrimp within this unit are found in a diversity of pool types, including Northern Volcanic Mudflow vernal pools on Pardee and Pentz soils, vernal pools occurring on low terrace landforms associated with San Joaquin soils, and vernal pools occurring on high terrace landforms associated with Redding and Corning soils. These pool types provide a diversity of habitats for this species. The large vernal pool complexes found within this unit provide relatively undisturbed, hydrologically intact vernal pool habitats that support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp.

Many areas within this unit include actively restored and created vernal pools that support occurrences of vernal pool fairy shrimp (CNDDB 2001). This unit is also proposed as critical habitat to encourage that special management actions will be taken so that these areas continue to provide the necessary timing and length of inundation for vernal pool fairy shrimp survival. In many cases, the special management action necessary will simply be to monitor vernal pool hydrology to verify the success of the restoration effort.

This unit contains a number of conservation areas established specifically to contribute to the conservation of vernal pool fairy shrimp, and to compensate for the loss of thousands of acres of vernal pool grassland habitats throughout the Sacramento Valley. Many areas within this unit are managed specifically to provide habitat for migratory waterfowl, this unit also provides essential habitat for avian species that aid in the dispersal of vernal pool fairy shrimp and other vernal pool crustacean cysts.

This unit contains state and federally owned land, as well as private properties. Portions of the Cosumnes River Preserve occur within this unit. The Cosumnes River Preserve is jointly owned and managed by a variety of state, local, and Federal agencies including the BLM , CDFG, Ducks Unlimited, Inc., California Department of Water Resources, Sacramento Co. Dept. of Regional Parks, Open Space, and Recreation, TNC, and the Wildlife Conservation Board. The Cosumnes River Preserve encompasses and protects thousands of acres of wetlands and adjacent uplands, oak woodlands, and riparian forests along the Cosumnes River, the only undammed river on the west slope of the Sierra. The Cosumnes floodplain is a haven for tens of thousands of migratory waterfowl, songbirds, and raptors, a large portion of the Central Valley's population of greater sandhill cranes, and for rare reptiles and mammals like the river otter and threatened giant garter snake. Several large, diverse, vernal pool landscapes are protected within this unit including the Howard Ranch and Valensin Ranch. The Clay Station Mitigation Bank, Laguna Creek Mitigation Bank, and the Borden Ranch Mitigation site are included in this unit, as well as a number of smaller conservation areas including the Rancho Seco Preserve. Land ownership and protection within the unit includes CDFG (630 ha (1,557 ac)), TNC (3,988 ha (9,970 ac)) lands and WRP easements (4 ha (11 ac)). This area has been identified by the Sacramento Valley Open Space Conservancy, the CNPS, and TNC as an excellent example of vernal pool grasslands, supporting a rich and diverse community of vernal pool endemic plants and animals within Sacramento County. Urban expansion, conversion from grazing to other agricultural practices, particularly vineyards, have greatly affected existing vernal pool habitats throughout this unit.

This unit for vernal pool fairy shrimp occupies the area south of Deer Creek and Cosumnes River to just north of the Sacramento and San Joaquin county line near Simmerhorn Road. The eastern boundary is the low elevation foothills near the Amador county line. The western limit follows Dillard Road south to Colony Road near Herald. This unit also coincides with Unit 10 for vernal pool tadpole shrimp, and Unit 3 for Sacramento Orcutt grass. Other sensitive species found within this unit include Bogg's Lake hedge-hyssop, western spadefoot toad, legenere, California linderiella, California tiger salamander, Ahart's paronychia, Henderson's bent grass, Sanford's arrowhead, pincushion navarretia (Navarretia myersii ssp. deminuta), and dwarf downingia.

Unit 15 Vacaville Unit, Solano County (1,624 ha (4,012 ac))

This unit is proposed as critical habitat because it contains vernal pool fairy shrimp within large vernal pool complexes (Holland 1998, Solano County 2000, CNDDB 2001). This unit contains vernal pool fairy shrimp occurring within vernal pools and swales formed on Corning gravelly loam soil series, which form Northern Hardpan vernal pools (Sawyer and Keeler-Wolf 1995). These pool types maintain the necessary conditions for vernal pool fairy shrimp hatching, feeding, reproduction, and dispersal (CNDDB 2001).

The Vacaville Unit supports the only examples of Northern Hardpan vernal pool types, including high terrace vernal pools on Corning soils, on the western side of the valley. These unique habitats are necessary to maintain the diversity of habitats in which vernal pool fairy shrimp are known to occur. This unit is located primarily on private land although the State Land Commission owns approximately (60 ha (149 ac)) within this unit. Vernal pool habitats within this unit are threatened by urbanization from the expanding City of Vacaville. Solano County is currently developing a HCP which will address the conservation of vernal pool fairy shrimp in this area.

The Vacaville Unit is situated north and northeast of the City of Vacaville. The eastern boundary parallels Interstate 80, the northern boundary parallels Midway Road, and the western boundary is near Browns Valley Road. This unit also provides habitat for vernal pool tadpole shrimp, dwarf downingia, as well as Swainson's hawks (Buteo swainsoni) and burrowing owls.

Unit 16, Jepson Prairie Unit, Solano County (34,910 ha (86,261 ac))

We propose this area as critical habitat for vernal pool fairy shrimp because it supports numerous occurrences of the species (CNDDB 2001) living within systems of hydrologically interconnected pools and swales within a matrix of surrounding uplands that together form hydrologically and ecologically functional vernal pool complexes. These features contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp are known to occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth and reproduction, and dispersal. These features have been identified and mapped by Solano County (2000), Holland (1998), and the Solano County Farmlands and Open Space (2000). The Jepson Prairie Unit encompasses the greater Jepson Prairie grassland area, one of the most pristine, intact vernal pool ecosystems remaining in California. Jepson Prairie contains large, playa-like vernal pools which may be over several acres in size, including the 32 ha (80 ac) Olcott Lake. These larger pools often occur in complexes with smaller pools and hogwallow depressions.

This unit includes one of only two large contiguous areas of habitat remaining for vernal pool fairy shrimp on the floor of the Central Valley. The relatively undisturbed, hydrologically intact condition of the Jepson Prairie increases the likelihood that it will continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. This unit also provides essential habitat for migratory waterfowl that aid in the dispersal of vernal pool fairy shrimp and other vernal pool crustacean cysts. Vernal pool fairy shrimp in the Jepson Prairie grassland area inhabit unique combinations of low terrace and basin rim landform vernal pools on a diversity of soil types.

Jepson Prairie has long been recognized as an outstanding example of vernal pool ecosystems. In 1987 the National Park Service (NPS) named Jepson Prairie a National Natural Landmark, a designation given to sites that provide high quality habitat for threatened or endangered species. Jepson Prairie is the target of ongoing conservation planning efforts and active management. As part of the UC Reserve System, this area also provides critical research opportunities for scientists to study vernal pool species, including vernal pool fairy shrimp.

The unit contains 1,038 ha (2,564 ac) owned and or administered by CDFG. Additional lands are owned by DOD (760 ha (1,879 ac)), California State Parks (15 ha (38 ac)), and the State Land Commission (109 ha (273 ac)). NRCS holds easements or agreements protecting 436 ha (1,090 ac) of private land in the unit under the WRP program. TNC also holds a conservation easement on 623 ha (1,558 ac) in the unit. The Jepson Prairie Preserve is jointly managed by the Solano County Land Trust and the UC Reserve System. CDFG owns several ecological reserves in the vicinity of Jepson Prairie. This unit also contains several privately owned mitigation areas, and portions of Travis Air Force Base. Within the greater Jepson Prairie grassland area, existing vernal pools are threatened by agricultural conversion, landfill expansion, power plant construction, and utility maintenance.

This unit is located in the southern portion of Solano County, southeast of Interstate 80 and the cities of Fairfield and Vacaville, north of Grizzly Bay and Montezuma Slough, west of the Sacramento River and the Solano and Sacramento County line, and south of Midway Road and the City of Dixon. The unit is bisected by Highway 13. This unit is also described as Unit 11 for vernal pool tadpole shrimp. This unit contains Unit 3 for Colusa grass, Unit 2 for Solano grass, Unit 3 for Conservancy fairy shrimp, and Unit 4 and portions of Unit 5 for Contra Costa goldfields. Other rare vernal pool species which occur in this unit include alkali milk-vetch (Astragalus tener var. tener), Ferris's milk-vetch, vernal pool small scale (Atriplex persistens), dwarf downingia, Delta green ground beetle (Elaphrus viridus), Bogg's Lake hedge-hyssop, Ricksecker's water scavenger beetle (Hydrochara rickseckeri), California linderiella, midvalley fairy shrimp, legenere, and California tiger salamander.

Unit 17, Napa River Unit, Napa and Sonoma Counties (656 ha (1,621 ac))

We propose this unit as critical habitat for vernal pool fairy shrimp because it contains vernal pools where vernal pool fairy shrimp are known to occur (CNDDB 2001). The boundaries of this unit were designed to include vernal pool complexes mapped by Holland (1998) and within the Fagan Marsh Ecological Area owned by the CDFG (420 ha (901 ac)) that contribute to the inundation patterns, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth and reproduction, and dispersal, but not necessarily every year. The minimum mapping unit of Holland (1998) of 16 ha (40 ac) and the resolution of the SPOT imagery did not allow us to identify all vernal pool habitat areas which provide the primary constituent elements for vernal pool fairy shrimp in this area. The unit boundary was designated to exclude tidal marsh habitats in the south, and urban and agricultural areas along the northern and eastern boundaries. The Napa River parallels the western boundary of this unit.

This unit represents the western extent of vernal pool fairy shrimp range. Such isolated and peripheral populations may be essential to the conservation of this species because of their genetic uniqueness (Fugate 1992, 1998, Lessica and Allendorf 1995). This unit represents the only area where vernal pool fairy shrimp occur in vernal pool habitats forming a transition zone with tidal marshes. This unit is located on private and CDFG land, including the Napa-Sonoma Marsh and Fagan Marsh Wildlife Areas. Habitats within this unit are primarily threatened by urbanization from the City of Napa.

Most of this unit is situated south and southwest of the City of Napa; primarily west of Highway 29, south of Highway 12, and east of Highway 121. This unit forms a narrow strip following the northwestern banks of the Napa River and extending westward along Hudeman and Schell sloughs. This unit is also identified as Unit 3 for Contra Costa goldfields. Other rare vernal pool species found in this unit include the alkali milk-vetch.

Unit 18, San Joaquin Unit, San Joaquin County (7,105 ha (17,557 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains vernal pool habitats identified by Holland (1998) and San Joaquin County (1998) that support populations of vernal pool fairy shrimp (CNDDB 2001). This unit contains vernal pool fairy shrimp occurrences found within Northern Volcanic Mudflow vernal pools on the Laguna geologic formation, as well as high terrace pools on the Valley Springs geologic formation. The Northern Volcanic Mudflow vernal pools tend to be short-lived, and are a relatively rare habitat type for vernal pool fairy shrimp. This unit contains the largest vernal pool complex remaining in San Joaquin County and the southern Sacramento Valley, and contains the necessary geographic, topographic, and edaphic features to support vernal pool fairy shrimp occurrences found within this unit. San Joaquin County has completed a HCP, which includes measures to protect conversion of vernal pool fairy shrimp habitat from vernal pools grasslands to vineyards. Conversion from grazing to other agricultural practices have greatly reduced the remaining acreage of vernal pool habitats throughout this unit.

This unit occupies the area from the Calaveras River south to Duck Creek. The eastern boundary extends to near Valley Springs at the intersection of State routes 12 and 26. The western boundary extends to near Tully Road east of the City of Lodi. This unit also coincides with Unit 14 for vernal pool tadpole shrimp. Other sensitive vernal pool species found within this unit include western spadefoot toad and California tiger salamander. All the land within this unit is privately owned.

Unit 19A, B, and C, Altamont Hills Unit, Contra Costa and Alameda counties (3,356 ha (8,292 ac))

This unit is proposed as critical for vernal pool fairy shrimp because it contains vernal pool habitats mapped by Holland (1998) and East Bay Regional Parks District (2001) supporting vernal pool fairy shrimp occurrences identified by CNDDB (2001). Vernal pool fairy shrimp have been discovered in very small (less than 1 m (3.3 ft) in diameter) clear water depression pools in sandstone outcrops in the area (Eriksen and Belk 1999). The unit represents the only known location that supports vernal pool fairy shrimp within sandstone outcrop pools (Eriksen and Belk 1999).

Vernal pool fairy shrimp in the Altamont Hills Unit are located over 60 km (40 miles) from the closest known occurrence to north in Solano County and to the south in Stanislaus County, and over 60 km (40 mi) from the next occurrence to the west in San Joaquin County. These populations may be genetically different from other vernal populations because of their relative isolation (Fugate 1998).

The unit is comprised of three subunits in the general vicinity of Mount Diablo and Morgan Territory Regional Park. The unit primarily consists of private land, with 64 ha (157 ac) owned by the state and an additional 288 ha (711 ac) administered by the California Department of Fish and Game for conservation purposes.

This unit overlaps Unit 7 for Contra Costa goldfields. The unit lies north of Corral Hollow Road, west of Clifton Court Forebay, east of the City of Danville, southeast of Concord, and south of Antioch. It includes vernal pool habitat within the Altamont Hills, around the northern and eastern boundaries of the City of Livermore, and east of the Altamont Hills and west of Clifton Court Forebay. The unit includes Fricke Lake which supports a large population of California tiger salamanders.

Unit 20, Caswell Unit, Stanislaus County (302 ha (746 ac))

This unit is proposed as critical habitat for vernal pool fairy shrimp because it contains vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated for sufficient lengths of time necessary for vernal pool fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, but which are dry during the summer (Holland 1998, CNDDB 2001). This unit also supports aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes (Holland 1998). These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool fairy shrimp hatching, growth and reproduction, and dispersal, but not necessarily every year. This unit includes vernal pool complexes mapped by Holland (1998) where vernal pool fairy shrimp have been documented by CNDDB (2001).

This unit is located within the San Joaquin River National Wildlife Refuge and efforts to restore vernal pool habitats are currently underway. Additional restoration designed to enhance habitat for riparian species, as well as migratory birds and waterfowl, is also being conducted. The San Joaquin River National Wildlife Refuge is the primary wintering site of 98 percent of the Aleutian Canada geese that winter in the Central Valley (October-April), and it is a major wintering and migration area for lesser and greater sandhill cranes, cackling Canada geese, and white-fronted geese. These migratory birds act as important dispersal agents for vernal pool fairy shrimp. Lands within this unit form a mosaic of riparian habitat, wetlands, and grasslands.

This unit is over 75 km (47 mi) from the nearest unit to the north. Such isolated populations may have genetic characteristics essential to overall long-term conservation of the species (i.e. they may be genetically different than more central populations) (Fugate 1992, 1998). This unit may be threatened by agricultural development, oil and natural gas exploration and development, and conversion from grazing to other agricultural practices. Water management practices may also threaten vernal pool fairy shrimp in this unit if natural vernal pool hydrology is altered.

This unit is situated west of the City of Modesto and east and southeast of the confluence of the San Joaquin and Stanislaus rivers. Caswell Memorial State Park lies just north of this unit and is not included. The San Joaquin River forms the western boundary of the unit. The unit is bisected by the Hetch Hetchy Aqueduct, State Highway 132, and the Tuolumne River. Roughly the northern one-third of this unit overlaps with Unit 5 for Conservancy fairy shrimp. It is also contains California linderiella and California tiger salamander occurrences, in addition to a number of rare non-vernal pool species, including the federally listed endangered riparian wood rat and riparian brush rabbit.

Unit 21, Stanislaus Unit, Stanislaus and Merced Counties (25,317 ha (62,557 ac))

This area is proposed as critical habitat for vernal pool fairy shrimp because it contains occurrences of the species within large, relatively intact, and contiguous vernal pool complexes ranging from the floor of the valley to the low elevation foothills (Holland 1998, CNDDB 2001). These areas are essential to the conservation of vernal pool fairy shrimp because they provide relatively undisturbed, hydrologically intact vernal pool habitats that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. This unit contains vernal pool fairy shrimp living within hardpan pools that occur on soils of alluvial fans and terraces forming numerous small pools and swales on mima mound topography. Soils supporting these vernal pools are typically older than those of the alluvial terraces in the Sacramento area. These pools provide the necessary timing and length of inundation for vernal pool fairy shrimp to complete their life cycle, reproduce, and disperse.

The Stanislaus Unit is in the northern portion of the chain of vernal pools that runs through the southern Sierra Nevada foothills, within the Southern Sierra Foothill vernal pool region described by Keeler-Wolf et al. (1998). This vernal pool region contains 35 percent of all remaining vernal pool habitat in the Central Valley, and is extremely important to the conservation of vernal pool fairy shrimp and other vernal pool species. Land ownership within this unit includes the BLM (7 ha (17 ac)) and the California State Parks (25 ha (61 ac)). The well-known Hickman pools in Stanislaus County are located within this unit. Not only does the Hickman pool complex contain one of the largest vernal lakes in California at more than 121 ha (300 ac), but it also exhibits tremendous biodiversity, including one of the largest concentrations of imperiled amphibians (Medeiros 2000). However, the watershed containing the Hickman vernal pools has been breached by hundreds of acres of orchards that have been planted upstream. While most of the watershed has been managed over the years in a trust of the Fred Robinson family, the integrity of the vernal pool ecosystem is threatened by agricultural development and potential biocide pollution (Medeiros 2000).

The Stanislaus Unit is located in the southeast corner of Stanislaus County and the northeast corner of Merced County. It lies between the Tuolumne River and the Merced River. The Mariposa County line is located east of the unit. Turlock Lake and Dawson Lake are adjacent to the northern boundary. County Road J9 and the High Line Canal are west of the unit. This unit coincides with vernal pool tadpole shrimp Unit 16. It includes succulent owl's-clover Unit 3, hairy Orcutt grass Unit 5, Colusa grass Unit 6, and Hoover's spurge Unit 5. Other sensitive vernal pool species found within this unit include western spadefoot toad, dwarf downingia, California linderiella, California tiger salamander, and Hartweg's golden sunburst (Pseudobahia bahiifloia).

Unit 22, Merced Unit, Merced and Mariposa Counties (44,106 ha (108,984 ac)

We propose this unit as critical habitat for vernal pool fairy shrimp because it encompasses the largest block of pristine, high density vernal pool grasslands supporting the species remaining in California (Holland 1998, Vollmar 1999, CNDDB 2001). These habitats provide the primary constituent elements essential for vernal pool fairy shrimp. There are more documented occurrences of vernal pool fairy shrimp in this unit than any other area throughout the species range (CNDDB 2001). Almost 15 percent of all remaining vernal pool habitats in the Central Valley are located within this unit (Holland 1998).

The Merced Unit is located midway in a chain of vernal pool complexes that straddles the valley floor and the foothills of the southern Sierra Nevada. This unit helps to maintain connectivity between vernal pool fairy shrimp habitats on the valley floor and habitats to the north and south of the Merced Unit. Genetic analyses of vernal pool tadpole shrimp revealed that occurrences in this unit were genetically different from other sampled occurrences in California, and that this area had likely been isolated from other vernal pool habitats for a significant period of time (King 1996). Given that vernal pool fairy shrimp and vernal pool tadpole shrimp are dispersed in similar ways, it is reasonable to assume that vernal pool fairy shrimp occurrences in this area are also isolated from other occurrences throughout its range.

This unit contains habitat for three listed branchiopods, six listed plants, and a suite of sensitive species. Forty percent of vernal pool habitats in the Southern Sierra Foothill vernal pool region are found within this unit. The integrity of the vernal pool complexes in eastern Merced is seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced Campus and associated development. Construction of facilities to educate and serve twenty-five thousand UC students as well as faculty, staff, and their families within the vernal pool complexes in eastern Merced County could have a major impact on vernal pool fairy shrimp occurrences. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Indirect and cumulative impacts of the proposed 1,673 ha (4,133 ac) campus and associated community may be minimized with the creation of a 2,036 ha (5,030 ac) preserve intended to protect sensitive vernal pool habitat, to be purchased with money donated by the Packard Foundation.

A majority of vernal pool habitat in the Merced Unit is in Merced County. The eastern edge of the unit overlaps into Mariposa County. Bear Creek flows along the southern boundary of the unit, crossing through it in several locations. The City of Merced is south of the unit, Bear Reservoir is southeast of the unit and the Castle Airport is located outside of the southwest boundary. The northern boundary parallels the Merced River. The entire unit is located east of Highway 99. Land ownership within the unit includes approximately 3 ha (8 ac) of BLM, and 10 ha (26 ac) of California State Parks. TNC has a total of 4,513 ha (11,283 ac) of conservation easements within this unit. The Merced Unit coincides with vernal pool tadpole shrimp Unit 13, succulent owl's-clover Unit 4, San Joaquin Valley Orcutt grass Unit 2, Colusa grass Unit 7, and Conservancy fairy shrimp Unit 6. Other sensitive vernal pool species found within this unit include the California tiger salamander, shining navarretia (Navarretia nigelliforms ssp radians), dwarf downingia, Bogg's Lake hedge-hyssop, western spadefoot toad, and California linderiella.

Unit 23, Grassland Ecological Unit, Merced County (55,910 ha (138,153 ac))

We propose this unit as critical based upon the presence of vernal pools and vernal pool fairy shrimp. This unit supports numerous occurrences of vernal pool fairy shrimp within a diversity of vernal pools supported by a number of different soil types, including Delhi-Dello-Himar, Solano-Caypay-Willows, Rossi-Waukena, and Lewis-Landlow soils (CNDDB 2001, USDA 2001). This diversity of soils creates a wide range of vernal pool shapes, sizes, and physical characteristics which provide the essential timing, frequency, and length of inundation necessary for the conservation of the species. This unit contains numerous large, intact vernal pool grasslands, and is one of only two areas on the floor of the Central Valley that provide expansive areas of vernal pool complexes within which vernal pool fairy shrimp can hatch, mature, and reproduce. These areas will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool fairy shrimp. This unit also provides habitat for migratory waterfowl that aid in the dispersal of vernal pool fairy shrimp and other vernal pool crustacean cysts. This is the only area where all four vernal pool crustaceans addressed in this proposed rule are known to co-occur.

The Grasslands Unit includes Kesterson, San Luis, and Merced National Wildlife Refuges, as well as several Federal and State conservation easement areas, lands owned by the California State Parks and Wildlife Areas, and private lands. Land ownership within the unit includes the Service (13,943 ha (34,452 ac)), CDFG lands (1703 ha (4,257 ac)), California State Parks (1,357 ha (3,392 ac)), CDFG administered lands (1,052 ha (2,631 ac)) and WRP conservation easements (54 ha (134 ac)). All other lands within this unit are privately owned. Together, these areas are known as the Grasslands Ecological Area. This area supports diverse wetland habitats including seasonally flooded marshlands, semi-permanent marsh, riparian habitat, wet meadows, vernal pools, native uplands, pastures, and native grasslands. Wetlands within this area, including seasonal marsh and open water habitats, constitute 30 percent of the remaining wetlands in California's Central Valley and are extremely important to Pacific Flyway waterfowl populations. Over 60 million duck use-days and 3 million goose use-days occur annually in this unit. This habitat also supports a diversity of other migratory birds, including raptors, shorebirds, wading birds, and other wildlife species.

This unit contains over 50 percent of the remaining vernal pool habitats within the San Joaquin Valley identified by Holland (1998). This area is an important portion of the geographic distribution of vernal pool fairy shrimp within the San Joaquin Valley. Threats to vernal pool fairy shrimp within this unit include conversion to agriculture, changes in hydrology, invasion by aggressive plants, and certain wetland management practices.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit also represents Unit 24 for tadpole shrimp. The western half of this unit also represents Unit 2 for longhorn fairy shrimp and the eastern half represents Unit 8 for Colusa grass, Unit 8 for Hoover's spurge, and Unit 7 for Conservancy fairy shrimp. In addition to the species mentioned above, other sensitive vernal pool species occur within the unit including Hispid's bird beak, Sanford's arrowhead, heartscale, brittlescale, vernal pool smallscale, delta button celery, alkali milk-vetch, California tiger salamander, western spadefoot toad, and California linderiella.

Unit 24A and B, Madera Unit, Madera and Fresno Counties (17,232 ha (42,579 ac))

The Madera Unit is proposed as critical habitat for vernal pool fairy shrimp because it contains occurrences of the species living within hardpan vernal pool complexes composed of numerous small pools and swales on mima mound topography (Holland 1998, Keeler-Wolf et al. 1998, CNDDB 2001). These vernal pools occur on alluvial fans and terraces and provide the necessary timing and duration of inundation essential to the conservation of vernal pool fairy shrimp. South of this unit in Fresno County these pools become less common as the soils that support them are less widespread (Keeler-Wolf et al. 1998).

Located in western Madera County, this unit is located between the Fresno River and San Joaquin River. Land ownership within this unit includes 0.4 ha (1 ac) of CDFG lands. All other land within this unit is privately owned. All vernal pools in this unit are located east of Highway 99 and the Atchison, Topeka, and Santa Fe Railroad, extending east toward the low elevation foothill region of the Sierra Nevada. State Route 145 bisects the unit. The Madera Unit encompasses San Joaquin Valley Orcutt grass Unit 5a, hairy Orcutt grass Unit 7, and succulent owl's-clover Unit 7a. Other sensitive vernal pool species found within this unit include California linderiella, California tiger salamander, and western spadefoot toad.

This unit consists of two subunits. Subunit A contains vernal pool habitats south of Millerton Lake. The western boundary of this unit is bordered by the San Joaquin River. Gordon Road cuts through the southernmost tip of the unit. Owens Mountain and Table Mountain Rancheria are located east of the Unit. The Friant Kern Canal crosses through the unit in a southeasterly direction. Subunit B is located mostly west of State Route 41 along Little Dry Creek and Cottonwood Creek.

Unit 25, Kennedy Table Unit, Madera County (994 ha (2,456 ac))

We propose this unit as critical habitat because it contains vernal pools and vernal pool fairy shrimp (Holland 1998, CNDDB 2001). Vernal pool fairy shrimp within this unit live within rare Northern Basalt Flow vernal pool complexes that provide the necessary topographic and edaphic conditions essential to the conservation of the species. Northern Basalt Flow vernal pools within this unit are perched on narrow, sinuous basalt mesas above the surrounding low-lying terrain, and typically contain small, irregularly clustered pools with “flashy hydrology” (pools fill and dry quickly) (Keeler-Wolf et al. 1998). These pool types provide the necessary timing and length of inundation for vernal pool fairy shrimp to hatch, mature, and reproduce, but do not stay inundated long enough to allow the invasion of aquatic species (CNDDB 2001). The Kennedy Table Unit is over 50 km (31 mi) from the next closest unit to the south and over 65 km (40 mi) from the nearest unit to the north. Such peripheral populations may have genetic characteristics essential to overall long-term conservation of the species (i.e., they may be genetically different than more central populations) (Fugate 1998).

This unit is located north and west of the Fresno County line on Kennedy Table in Madera County. It is northeast of Millerton Lake, and the San Joaquin River flows east and south of it. Land ownership within this unit includes 65 ha (161 ac) of BLM lands. All other land within this unit is privately owned. This unit coincides with vernal pool tadpole shrimp Unit 19, succulent owl's-clover Unit 8A and B, San Joaquin Valley Orcutt grass units 5B and 6A, and hairy Orcutt grass Unit 10. In addition to these federally listed species other sensitive vernal pool species found within this unit include California linderiella, California tiger salamander, and the western spadefoot toad. In addition to these, the federally endangered Hartwig's golden sunburst also occurs within this unit.

Unit 26A, B, and C, Cross Creek Unit, Tulare and Kings Counties (3,193 ha (7,891 ac))

This unit is proposed as critical for vernal pool fairy shrimp because it contains vernal pools that support occurrences of the species (Holland 1998, CNDDB 2001). Vernal pool fairy shrimp in this area occur in vernal pools formed on Lewis and Youd soils (USDA 2001). This area represents the southern extent of vernal pool fairy shrimp range along the eastern margin of the Central Valley, and is the largest contiguous vernal pool habitat in this region (Holland 1998, CNDDB 2001).

This unit contains the CDFG's Sequoia Field and Stone Corral Ecological Reserves in Tulare County. These reserves are one of the few vernal pool conservation areas in the eastern portion of the San Joaquin Valley, and they have been the focus of several monitoring and management efforts. Land ownership within this unit includes 348 ha (861 ac) of CDFG lands. All other land within this unit is privately owned. TNC, Tulare County, and the Sierra Los Tulares Land Trust have identified this area as one of the best remaining examples of vernal pool habitats in the region. Much of the vernal pool habitat within Tulare County has been severely degraded and converted. The conversion of habitat adjacent to this unit to urbanized areas, orchards, and other forms of irrigated agriculture continues to threaten the long-term viability of the vernal pools within this unit.

This unit is comprised of three subunits. Subunit A is located in northwest Tulare County and contains vernal pool habitat located west of Seville. The Friant Kern Canal is north of the unit and the Cottonwood Creek Levee is south of the unit. Road 140 runs west of the unit. Subunit B contains vernal pools in northeastern Kings County and northwestern Tulare County. Highway 99 and St. Johns River cut through the unit in a southeasterly direction. Cross Creek and Cottonwood Creek cut through the unit in a southwesterly direction. Road 112 is east of the unit and the Lakeland Canal is west of the unit. The towns of Goshen and Visalia are south of the unit and Traver and London are north of the unit. Subunit C is known as Sequoia Field Unit and is located in northwestern Tulare County. This unit is south of County Road J36. Road 112 crosses through the western edge of the unit, Avenue 352 crosses through the southern edge, and State Route 63 crosses through the eastern edge. The Cross Creek Unit coincides with vernal pool tadpole shrimp Unit 20 and contains portions of San Joaquin Valley Orcutt grass Unit 8 and Hoover's spurge Unit 9. Other sensitive vernal pool species found within this unit include the California tiger salamander, spiny-sepaled button-celery, and western spadefoot toad.

Unit 27A and B, Pixley Unit, Tulare County (7,842 ha) 19,377 ac))

This unit is proposed for vernal pool fairy shrimp because it contains the largest contiguous area of habitat for the species in the southern portion of the San Joaquin Valley, and supports vernal pools that provide the necessary timing and length of inundation essential to the conservation of vernal pool fairy shrimp (Holland 1998, CNDDB 2001). Vernal pool fairy shrimp in this area occur within Northern Claypan vernal pools that tend to be alkaline and larger than other vernal pool fairy shrimp habitats, such as those found on the eastern margin of the San Joaquin Valley.

This unit contains wintering areas for migratory waterfowl, shorebirds, marsh, and waterbirds in the southern San Joaquin Valley, and include natural valley grasslands and developed marsh habitats within the Pixley National Wildlife Refuge complex (2,742 ha (6, 776 ac)). Other ownership within this unit include CDFG (490 ha (1,210 ac)) and TNC lands (1,309 ha (3,274 ac)). All other lands within this unit are privately owned. These habitats are important for migratory waterfowl that aid in the dispersal of vernal pool fairy shrimp and other vernal pool crustacean cysts. This unit represents one of only three areas designated for vernal pool fairy shrimp in the San Joaquin Valley vernal pool region described by Keeler-Wolf et al. (1998). The refuge also provides habitat for the endangered San Joaquin kit fox and the blunt-nosed leopard lizard. Vernal pool fairy shrimp within this unit are threatened by agricultural development, oil and natural gas exploration and development, subdivision of ranches and land grants, urban expansion, and conversion from grazing to other agricultural practices.

This unit consists of two subunits that lie south of the Cities of Hanford and Lemoore, north of the City of Wasco, and east of the City of the Tulare. In addition to vernal pool fairy shrimp, western spadefoot toad and California tiger salamander are present within this unit.

Unit 28, San Benito County Unit, San Benito and Monterey Counties (48,125 ha (118,915 ac))

The San Benito County unit is located in the southwestern portion of San Benito County and the eastern-most portion of Monterey County. This unit consists of a distinct collection of seasonally flooded wetlands west of the Great Central Valley, and overlaps a portion of the Central Coast vernal pool region that has been delineated by the CDFG (Keeler-Wolf et al. 1998). The proposed critical habitat unit contains a minimum of 13 vernal pool complexes that are 7 to 144 ha (17 to 356 ac) in size, and also includes a number of unmapped vernal pools or pool complexes that are less than 4 ha (10 ac) in size. Focused surveys for vernal pool fairy shrimp have not been conducted within the proposed critical habitat unit, and it is therefore likely that this species is present in many, if not most, of the vernal pool complexes that have not been censussed due to habitat similarity to where the occurrences have been documented. This conclusion is supported by the fact that two-thirds of vernal pool fairy shrimp occurrences that have been documented within the critical habitat unit were not located within large vernal pool complexes, but were instead found in smaller, unmapped vernal pools. Land ownership within this unit includes BLM (1,581 ha (3,906 ac)) and State Land Commission (2 ha (5 ac)). All other lands within this unit are privately owned. The critical habitat unit perimeter is defined by the presence of low slope areas within watershed boundaries that are known to contain vernal pool fairy shrimp occurrences and vernal pool habitats. Conservation of vernal pools in the San Benito County unit is necessary to maintain and restore occurrences of vernal pool fairy shrimp that are disjunct from other listed fairy shrimp localities in the Great Central Valley.

Unit 29A, B, and C, Central Coastal Ranges Unit, Monterey and San Luis Obispo Counties (41,054 ha (101,444 ac))

The Central Coastal Ranges Unit includes three subunits that occur in Monterey and San Luis Obispo counties. The three subunits include areas at or adjacent to Fort Hunter Liggett, Camp Roberts, and the city of Paso Robles. The vast majority of the Fort Hunter Liggett subunit overlaps the military reservation, and also includes a small portion of privately owned land east of the military base. Land ownership within this unit includes DOD (20,585 ha (50,866 ac)) and BLM (1 ha (2 ac)). All other lands within this unit are privately owned. Intensive surveys on Fort Hunter Liggett have documented the occurrence of listed fairy shrimp in a minimum of 65 different pools within the base boundary (Fort Hunter Liggitt 2000). Several additional pools in restricted access areas on the base have not been surveyed, and some of these are also likely to possess listed fairy shrimp. The majority of the Camp Roberts subunit includes land within that military base boundary, and includes a limited amount of privately owned land north and southeast of the military base. Surveys on Camp Roberts have documented the presence of vernal pool fairy shrimp at 61 sites (Jones and Stokes 1997a). One hundred and nineteen additional sites were also found to possess unidentified juvenile fairy shrimp, and the inability to document the presence of other fairy shrimp taxa on the base suggests that these pools are therefore likely to contain listed species. The Paso Robles subunit consists of a polygon that is 3.2 to 24 km (2 to 15 mi) northeast of the city boundary. A limited number of surveys for fairy shrimp within the subunit have been conducted by California Department of Transportation staff along State Highway 46. These surveys have documented the occurrence of vernal pool fairy shrimp within the subunit (Mitch Dallas, California Department of Transportation, pers. comm.). The Paso Robles subunit possesses several large vernal pool complexes that are 42,314 ha (105,776 ac) in size. The discovery of vernal pool fairy shrimp in the area 6 km (4 mi) east of the city suggests that the species is likely to be widely dispersed in remnant vernal pools or complexes that still exist within the critical habitat subunit. The Fort Hunter Liggett subunit occurs within the Central Coast vernal pool region that has been delineated by the CDFG (Keeler-Wolf et al. 1998), and the Camp Roberts and Paso Robles subunits occur within the Carrizo vernal pool region. The subunit perimeters are defined by the presence of low slope areas within watershed boundaries that are known to contain vernal pool fairy shrimp and vernal pool habitats. Conservation of vernal pools in the region is necessary to stabilize and recover remnant populations of vernal pool fairy shrimp in the central coastal county area of southern California.

Unit 30, Carrizo Plain Unit, San Luis Obispo County (10,466 ha (25,862 ac))

This unit is proposed as critical for vernal pool fairy shrimp because it contains vernal pool habitats identified by Holland (2002) and that support occurrences of vernal pool fairy shrimp (CNDDB 2001). Vernal pool fairy shrimp found in the Carrizo Plain live within Northern Claypan vernal pools (Sawyer and Keeler-Wolf 1995) which occur in numerous shallow alkaline depressions within a Valley Saltbush Scrub matrix. These pools provide all of the primary constituent elements essential for the conservation of vernal pool fairy shrimp, as well as the edaphic and geologic features necessary to maintain the hydrology of the vernal pool complexes.

Many vernal pools in the region are adjacent to the 1,214 ha (3,000 ac) Soda Lake, the largest alkali wetland in central and southern California, which provides a winter haven for thousands of migratory birds. Vernal pool fairy shrimp in the Carrizo Plain Unit are located 235 km (146 mi) southeast of the closest known occurrences at Kesterson National Wildlife Refuge in Merced County. Such isolated and peripheral populations may have genetic characteristics that are different than more central populations, and may be important for conservation (Lesica and Allendorf 1995, Fugate 1998). The Carrizo Plain Unit is the only area where vernal pool fairy shrimp are known from saline salt brush scrub vernal pool habitats.

The Carrizo Plain contains examples of native bunch grass, needle grass, and blue grass grasslands, as well as populations of federally listed San Joaquin kit fox, blunt nosed leopard lizard, giant kangaroo rat, California jewel flower, Lost Hills salt brush, Kern mallow and San Joaquin wooly threads. Most of the habitat within this unit is part of the Carrizo Plain National Monument, which is administered by the BLM, TNC, and the CDFG. The BLM lands within the unit total approximately 6,220 ha (15,549 ac) and the CDFG lands total approximately 93 ha (233 ac). Other vernal pool habitats in the unit are located on private land.

This unit includes vernal pool habitat in the interior basin of the Carrizo Plain. It encompasses California Valley and Soda Lake. State Highway 58 is located north of the unit. Most of the habitat is east of Soda Lake Road, however, Soda Lake Road crosses through the western edge of the unit in several areas. To the east, the unit is bordered by the San Andreas Rift Zone. This unit coincides with longhorn fairy shrimp Unit 3.

Unit 31, Lake Cachuma Area, Santa Barbara County (8,399 ha (20,754 ac))

The Lake Cachuma critical habitat unit is located within a 16 km (10 mi) radius of the northwestern portion of Lake Cachuma in central Santa Barbara County. The unit boundary has been delineated to include hydrologic units that contain vernal pool fairy shrimp and vernal pool habitats. Vernal pool complexes within the unit vary in size from 16 to 81 ha (40 to 199 ac). Surveys for fairy shrimp species have rarely been conducted within the unit. A portion of the unit overlaps the Santa Barbara vernal pool region that has been delineated by the CDFG (Keeler-Wolf et al. 1998). The Lake Cachuma unit is essential for the conservation of vernal pool fairy shrimp because it contains seasonally flooded aquatic environments that contain markedly disjunct species occurrences. Landownership within this unit includes U.S. Forest Service (USFS) (2,199 ha (5,434 ac)) and BLM (37 ha (92 ac)). Other land within this unit is privately owned.

Unit 32, Ventura County Unit, Ventura County (18,831 ha (46,531 ac))

The Ventura County unit is located in the north-central portion of Ventura County. All the lands within this unit are owned by the USFS. Vernal pool fairy shrimp and Conservancy fairy shrimp are known to co-occur at relatively high elevation (~1700 m (5500 ft)) forested sites within the Los Padres National Forest. Almost all of the known localities that possess these two species within the state of California exist at much lower elevations in grassland habitats. The critical habitat perimeter consists of an area that is known to contain vernal pool and Conservancy fairy shrimp occurrences and isolated pools that provide habitat for the two species. Fairy shrimp surveys have rarely been conducted in the proposed critical habitat unit. The Ventura County unit is essential for the conservation of vernal pool fairy shrimp because it contains ephemeral aquatic environments that are rarely associated with fairy shrimp, and the occupied sites represent markedly disjunct occurrences for the species.

Unit 33A, B, and C San Jacinto-Hemet Unit, Riverside County (2,319 ha (5,730 ac)).

This unit lies in the southern portion of the San Jacinto Valley and contains two primary subunits (San Jacinto and Hemet), the latter of which is itself divided into two smaller subunits (33B and 33C). Unit 33 consists of the remnant alkali playa associated with the San Jacinto River (subunit A) and the upper Salt Creek drainage (subunits B and C). Large portions of the alkali willow soils associated with these watercourses have been historically altered by drainage projects and agriculture resulting in the degradation or destruction of vernal pool habitat. The unit consists of areas where vernal pool fairy shrimp remain extant and/or where essential hydrology and alkali soils are intact supporting vernal pool and alkali playa habitat. All the lands within this unit are privately owned.

The San Jacinto primary subunit (subunit 33A) consists of lands along the San Jacinto River floodplain from the Ramona Expressway westward past Interstate 215 to the upper reaches of the northern portion of Railroad Canyon Reservoir. The lands delimited by this subunit represent the largest remaining contiguous alkali playa/vernal pool habitat within the historic range of vernal pool fairy shrimp in southern California. The subunit contains multiple extant vernal pools and complexes scattered along the river floodplain with intact water circulation processes and alkaline soil substrates preferred by vernal pool fairy shrimp.

A presence/absence survey for federally listed fairy shrimp was conducted in a portion of the pools in this subunit in the spring of 2000. No listed fairy shrimp were detected. However, not all vernal pool basins filled in the spring of 2000, and of those that did, not all retained water throughout the sample period. Additionally, no survey for fairy shrimp cysts (dry season survey) has been conducted. Therefore, the survey effort is inconclusive for the presence of listed fairy shrimp species. However, the common versatile fairy shrimp (Branchinecta lindahli) was detected in these pools (Bomkamp 2000). Further, the threatened spreading navarretia (Navarretia fossalis), the threatened thread-leaved brodiaea (Brodiaea filifolia), and the endangered San Jacinto Valley crownscale (Atriplex coronatum var. notatior) have also been documented within this subunit. These species are all associated with vernal pool and alkali playa habitats.

Even though the presence of vernal pool fairy shrimp in the San Jacinto River floodplain has not been established, the vernal pool alkali playa habitat of subunit 33A is considered to be essential for the conservation of vernal pool fairy shrimp in southern California. As previously indicated, these pools contain the largest remaining contiguous alkali playa/vernal pool habitat within the historic range of vernal pool fairy shrimp in southern California, as well as appropriate water circulation patterns, alkali soils, and relatively close proximity to the occupied Hemet primary subunit.

The Hemet primary subunit (subunits 33B and 33C) include the west Hemet vernal pool complex along Florida Avenue (subunit 33B), as well as a small area east of Warren Road and north of Tres Cerritos (subunit 33C). Vernal pool fairy shrimp have been documented in the southwestern portion of the vernal pool complex. The remainder of this proposed subunit contains lands within the watershed of the occupied pool complex and other vernal pools in the basin. Lands within the watershed have been included to maintain the integrity of the surface flow and water quality to the pool complexes and playa overall.

In addition to vernal pool fairy shrimp, several federally listed plants including the threatened spreading navarretia, the threatened thread-leaved brodiaea, the endangered California Orcutt grass (Orcuttia californica), and the endangered San Jacinto Valley crownscale have also been documented within this subunit. These species are all associated with vernal pool and alkali playa habitats.

Unit 33 includes areas where vernal pool fairy shrimp are extant and recovery value for this species is high because of appropriate hydrology, soils and alkali vernal pool habitat. The alkali soils and their associated hydrology in the unit are essential to the conservation of vernal pool fairy shrimp in southern California (Service 1998).

Unit 34, Santa Rosa Plateau Unit, Riverside County (1,718 ha (4,246 ac))

The Santa Rosa Plateau critical habitat unit is on a large mesa made of basaltic and granitic substrates within the Santa Rosa Plateau Ecological Reserve. The unit contains one of the largest remaining vernal pool complexes in southern Riverside County and includes a series of large and small pools in which several sensitive or federally listed fairy shrimp have been documented. These include the vernal pool fairy shrimp (Angelos 1998), the endangered Riverside fairy shrimp (Streptocephalus woottoni) (Service 2001), and the Santa Rosa fairy shrimp (Linderiella santarosae) (Angelos 1998). Additionally, the federally endangered California Orcutt grass is documented from the pool complex (Service 1998). This unit was designated as critical habitat for the Riverside fairy shrimp on May 30, 2001 (66 FR 29384). This vernal pool complex represents the southwestern limit of occupied vernal pool fairy shrimp habitat. It is also a unique habitat for vernal pool fairy shrimp, therefore, the fairy shrimp in these pools may have genetic characteristics important to the overall long-term conservation of the species (i.e., they may be genetically different from more centrally located populations) (Lesica and Allendorf 1995). Conservation of this vernal pool basin and its associated watershed is essential to the conservation of the vernal pool fairy shrimp, and the Riverside fairy shrimp in southern California, as indicated in the Vernal Pools of Southern California Recovery Plan (Service 1998). Property ownership and protection within this unit includes CDFG (761 ha (1,880 ac)), TNC (77 ha (1,902 ac)), and TNC conservation easements (150 ha (375 ac)).

Unit 35, Skunk Hollow Unit, Riverside County (97 ha (239 ac))

The Skunk Hollow vernal pool complex consist of a single, large (approximately 14 ha (35 ac)) vernal pool and its essential associated watershed in western Riverside County. All the lands within this unit are privately owned. Several federally listed species have been documented from the Skunk Hollow vernal pool basin. These include the threatened vernal pool fairy shrimp (Simovich in Litt 2001), the endangered Riverside fairy shrimp (Service 2001), the threatened spreading navarretia, and the endangered California Orcutt grass (Service 1998). The vernal pool complex and watershed is currently protected as part of a reserve established within an approved mitigation bank in the Rancho Bella Vista Habitat Conservation Plan (HCP) area and as part of the conservation measures contained in the Assessment District 161 Subregional HCP. While neither HCP include the vernal pool fairy shrimp as a covered species, both HCPs provide protection for the vernal pool complex and its associated watershed in perpetuity. Further, the HCPs address the endangered Riverside fairy shrimp as a covered species. Because we believed that the management and protections afforded the vernal pool complex and the Riverside fairy shrimp were adequate for the long-term conservation of this complex and this species, and it is in the long-term survival interest of the species to preserve the partnerships that we had developed with the local jurisdiction and project proponents in the development of the HCPs, we excluded the Skunk Hollow vernal pool complex from critical habitat for the Riverside fairy shrimp. We do not believe that this exclusion from critical habitat would result in the extinction of this Riverside fairy shrimp.

Even though the two HCPs do not have the vernal pool fairy shrimp listed as a covered species, we believe that the protections and management afforded the Skunk Hollow vernal pool complex and the other listed vernal pool species through the terms and conditions of those HCPs are adequate to ensure the long-term conservation of the vernal pool fairy shrimp as well. Therefore similar to the Riverside fairy shrimp, we believe that the benefits of the exclusion of the Skunk Hollow vernal pool complex from critical habitat for the vernal pool fairy shrimp outweighs the benefit of its inclusion. Additionally, we do not believe that this exclusion would result in the extinction of the vernal pool fairy shrimp.

Vernal Pool Tadpole Shrimp Criteria

In proposing critical habitat units for vernal pool tadpole shrimp we evaluated the life history and current distribution of the species, the primary constituent elements, and the threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of vernal pool tadpole shrimp and to delineate units so that threats to this species might be minimized.

CNDDB (2001) estimates that 32 percent of the remaining occurrences of this species are threatened by development and agricultural conversion. Other vernal pool tadpole shrimp occurrences are threatened by off road vehicle use, road construction and maintenance, mining, and landfill construction (CNDDB 2001). Several occurrences are threatened by intentional discing and draining of their habitats (CNDDB 2001). Vernal pool tadpole shrimp occurrences have been extirpated as a result of urban development, primarily in Sacramento and Tehama counties.

Numerous occurrences of vernal pool tadpole shrimp are threatened by altered hydrology. In some cases vernal pool tadpole shrimp habitat has been altered so that it contains water year round, allowing predators such as bullfrogs and fish to colonize the areas (CNDDB 2001). In other cases artificial run off has resulted in the delivery of materials that destroy vernal pool water quality, including pesticides from vineyards and other irrigated agricultural lands, pesticides from golf courses, and sediment from surrounding developments (CNDDB 2001). Several vernal pool tadpole shrimp occurrences are threatened by wetland management activities that are designed to transform their vernal pool habitats into permanent marshes for the benefit of other species (CNDDB 2001). Several other occurrences are threatened by the construction of drainage ditches, which artificially drain vernal pool tadpole shrimp habitats (CNDDB 2001).

Vernal Pool Tadpole Shrimp Unit Review

We conducted a regional review across the current range of vernal pool tadpole shrimp to evaluate and select areas that are essential to the conservation of the species and that may require special management actions. Important factors we considered were the presence of vernal pool tadpole shrimp and the presence of the primary constituent elements essential to the conservation of the species. We identified areas that support vernal pool tadpole shrimp occurrences identified by CNDDB (2002) within large vernal pool complexes mapped by Holland (1998) and other local sources throughout the range of the species. We have identified the areas necessary to maintain vernal pool tadpole shrimp range and distribution and to include some of the different kinds of habitats in which the species is known to occur. A specific description of each area is outlined below.

Unit 1, Stillwater Plains Unit, Shasta County (1,849 ha (4,569 ac))

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains the species (CNDDB 2002) within vernal pools mapped by Holland (1998) which are found on old alluvial terraces above the Sacramento River, often on Redding and Corning soil complexes (Shasta County 2001). Generally these pools range in size, from small (10 m²) (30 sq ft.) to several ha (ac) in size at the Stillwater Plains area. These vernal pools provide feeding and sheltering habitat for the species and remain inundated for sufficient lengths of time to allow vernal pool fairy shrimp to hatch, mature, and reproduce.

This unit represents critical habitat for vernal pool fairy shrimp because it contains all of the primary constituent elements for the species, and supports systems of hydrologically interconnected pools and swales within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustaceans to complete their life cycles.

The vernal pool tadpole shrimp within this unit were found to be genetically different from other populations, particularly those in the foothills of the Sierra Nevada (King 1996). This unit also comprises the northern extent of the species range in California, and such isolated populations may be essential to the overall long-term conservation of the species (Fugate 1992, 1998, Lesica and Allendorf 1995). The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp hatching, growth, reproduction, and dispersal.

This unit includes the Stillwater Plains Conservation Bank. The Stillwater Plains Conservation Bank was established specifically for the conservation of vernal pool tadpole shrimp, and has been used as mitigation for the destruction of other vernal pool tadpole shrimp habitats throughout the northeastern Sacramento Valley area. Most of the land included within this unit is privately owned, but 52 ha (130 ac) of that is protected by WRP easements or agreements. The BLM owns 17 ha (42 ac). Urban expansion from the Redding Area, and conversion from grazing to other agricultural practices continue to threaten vernal pool tadpole shrimp occurrences throughout this unit.

This unit is located in the area east of the Redding Municipal Airport between Airport Road to the west and Deschutes Road to the east. The unit extends to Dersch Road in the south and towards Lassen Park Highway in the north. This unit comprises a portion of the Stillwater Plains. This unit overlaps slender Orcutt grass Unit 2B and vernal pool fairy shrimp unit 5. Other sensitive species occurring within this unit include Red Bluff dwarf rush (Juncus leiospermus var. leiospermus), California linderiella (Linderiella occidentalis), Henderson's bent grass (Agrostis hendersonii), and four angled spike rush (Eleocharis quadrangulata).

Unit 2, Dales Unit, Shasta and Tehama Counties (20,446 ha (50,522 ac))

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains the species and vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths necessary for vernal pool tadpole to complete their life cycle (Holland 1998, CNDDB 2001). This unit is one of the few areas where vernal pool tadpole shrimp are known to occur in Northern Mudflow vernal pools. Northern Mudflow vernal pools are generally small and tend to be inundated for relatively short periods of time (Keeler-Wolf et al. 1998).

The boundaries of the unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool fairy shrimp occur, and which maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp hatching, growth, reproduction, and dispersal.

This unit contains some of the largest remaining vernal pool complexes supporting vernal pool tadpole shrimp in the northern portion of the species range, including the Dales Plains. These areas provide relatively undisturbed, hydrologically intact vernal pool habitats that will likely continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool tadpole shrimp. This unit also provides habitat for migratory waterfowl that aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts.

Land ownership within this unit includes BLM (6,226 (15,383 ac)), CDFG (392 ha (981 ac)), State Land Commission (40 ha (100 ac)). The CDFG administers approximately 17 ha (42 ac) and the TNC has conservation easements on 6,230 (15,575 ac) within this unit. The remaining lands included within this unit are privately owned. The CDFG has protected some vernal pool areas at Dales Lake Ecological Reserve. The importance of these vernal pool habitats has been recognized by a number of state, local, and Federal agencies, and they have been the focus of several conservation planning efforts. Portions of the CDFG Battle Creek Wildlife Area are found within this unit but the amount of vernal pool habitat currently protected within the unit is very small. Vernal pool habitats within this unit are fragmented and threatened by urban expansion, subdivision of ranches and land grants, and conversion from grazing to other agricultural practices.

This unit is located from Battle Creek on the Shasta/Tehama County line south of Balls Ferry to Paynes Creek near Dales. The vernal pool habitats west of Inskip Hill are included in this unit, as well as the area west of the Sacramento River known as Table Mountain and Table Mountain Lake. This unit coincides with Unit 3 for slender Orcutt grass. Other vernal pool species occurring within this unit include Bogg's Lake hedge-hyssop, Red Bluff dwarf rush, legenere, California linderiella, Ahart's paronychia, Henderson's bent grass, and Sanford's arrowhead.

Unit 3, Vina Plains Unit, Tehama and Butte Counties (23,883 ha (59,015 ac))

This unit is proposed as critical habitat because it contains occurrences of vernal pool tadpole shrimp (CNDDB 2001) living within large vernal pool grassland areas that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and within a matrix of surrounding uplands that together form hydrologically and ecologically functional units (EPA 1994, Holland 1998, Tehama County 1999). These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp hatching, growth and reproduction, and dispersal. This unit is one of the few areas where vernal pool tadpole shrimp are known to occur in Northern Basalt Flow vernal pools. Northern Basalt Flow vernal pools are limited to ancient terraces and hilltops that comprise some of the oldest geologic formations in California. This unit also provides habitat for migratory waterfowl that aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts.

This unit contains the vernal pool grassland area known as Vina Plains, which is managed by TNC. The Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating the effects of grazing and fire on vernal pool plants, animals, and ecosystems (Griggs 2000). Much of the basic life history information known about vernal pool crustaceans was collected at Vina Plains (e.g., Lanway 1974, Ahl 1991, Syrdahl 1993, Gallagher 1996).

The majority of the lands included within this unit are privately owned. This unit contains TNC's Vina Plains preserve as well as other TNC lands 2,264 ha (5,660 ac) and conservation easements 4,348 ha (10,870 ac). The unit also includes 57 ha (142 ac) of private lands protected by WRP easements or agreements. This unit is located in the northeastern portion of the Sacramento Valley from Deer Creek in Tehama County to Big Chico Creek north of Chico in Butte County. This unit is one of only two vernal pool tadpole shrimp units within the Northeastern Sacramento Valley vernal pool region identified by CDFG (Keeler Wolf et al. 1998). The unit extends south and east of the Sacramento River paralleling the low elevation foothill region of the Sierra Nevada. This unit coincides with Unit 7 for vernal pool fairy shrimp, and incorporates Unit 1 for Conservancy fairy shrimp, Units 4 for slender Orcutt grass, Unit 2 for Greene's tuctoria, Unit 1 for hairy Orcutt grass, Unit 1 for Hoover's spurge, and Units 1 and 2 for Butte County meadowfoam. Other vernal pool species occurring within this unit include Bogg's Lake hedge-hyssop, Red Bluff dwarf rush, Douglas' pogogyne, western spadefoot toad, legenere, California linderiella, California tiger salamander, Ahart's paronychia, Henderson's bent grass, Sanford's arrowhead , and dwarf downingia.

Unit 4, Oroville Unit, Butte and Yuba Counties (15,975 ha (39,474 ac))

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains occurrences of the species and vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths necessary for vernal pool tadpole shrimp to complete their life cycle (Holland 1998, CNDDB 2001, Silveira 2000). This unit contains some of the few areas where vernal pool tadpole shrimp are found in Northern Volcanic Mudflow vernal pools, including vernal pools found on the Tuscan and Lovejoy Basalt geologic formations. Vernal pool tadpole shrimp also occur within Northern Hardpan vernal pools in this unit, including pools formed on the Riverbank and Modesto geologic formations. King (1996) found that vernal pool tadpole shrimp at this site were genetically distinct from vernal pool tadpole shrimp at other locations.

The majority of the lands included within this unit are privately owned. Ownership and protected lands within the unit includes BLM (48 ha (119 ac)), USFS (78 ha (194 ac)), WRP easements (14 ha (35 ac)), and CDFG administered lands (69 ha (173 ac)). The CDFG has some vernal pool areas protected at the Oroville Wildlife Area, and some vernal pool habitats are protected within the City of Chico. However, the amount of vernal pool habitat currently protected within the unit is very small. Vernal pools in this unit are highly threatened due to their location on the lower elevation slopes adjacent to agricultural and urban development. Urban expansion, particularly in the vicinity of Chico, is the greatest threat to existing vernal pool habitats throughout this unit.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool tadpole shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp to hatch, feed, and reproduce.

This unit occupies the northeastern portion of the Sacramento Valley from near Chico south to the Yuba River in Yuba County. This area represents one of only two vernal pool tadpole shrimp units within the Northeastern Sacramento Valley vernal pool region identified by CDFG (Keeler Wolf et al. 1998). The unit extends southeast of the Sacramento River paralleling the low elevation foothill region of the Sierra Nevada. This unit incorporates portions of Unit 2 for Butte County meadow foam and fully incorporates Unit 9 for vernal pool fairy shrimp, Units 3 for Greene's tuctoria, Unit 2 for hairy Orcutt grass, Unit 2 for Hoover's spurge, and Unit 4 for Butte County meadowfoam. Other vernal pool species occurring within this unit include Bogg's Lake hedge-hyssop, Red Bluff dwarf rush, Douglas' pogogyne, western spadefoot toad, legenere, California linderiella, California tiger salamander, Ahart's paronychia, Henderson's bent grass, Sanford's arrowhead, and dwarf downingia.

Unit 5, Sacramento National Wildlife Refuge Unit, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it contains the primary constituent elements necessary for the conservation of the species, and supports occurrences of the species (Holland 1998, Silveira 2000, CNDDB 2001). Vernal pool tadpole shrimp within this unit live within Northern Claypan and Northern Hardpan vernal pools, as defined by Sawyer and Keeler-Wolf (1995). The edaphic features that support the formation of these vernal pools include the Modesto geologic formation and Willows and Riz soils series. These vernal pools occur on alkaline soils and typically form alkali playas which are larger and contain a more diverse species composition than the hardpan pools further south (Keeler-Wolf et al. 1998). They may resemble small alkali playas, and display white salt deposits following pool drying.

This unit is primarily located on the Sacramento National Wildlife Refuge (5,126 ha (12,816 ac)); however, additional private lands were included within this unit. The refuge supports over 355 native plant taxa, including a number of rare alkaline species. The Sacramento National Wildlife Refuge contains the only remnants of the widespread Colusa Plains vegetation that once covered the entire Colusa Basin (Silveira 2000). Vernal pool habitats on the refuge are specifically managed for the conservation of listed species, and to promote habitat for migratory birds and waterfowl. These avian species likely aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts. Vernal pool habitats within the area have become greatly fragmented and isolated from other habitats in the region due to agricultural and urban land conversion.

This unit occurs east of Interstate 5 to the Colusa Trough from Riz Road on the north and Delevan Road on the south. This unit coincides with Unit 1 for Colusa grass, Unit 6 for Greene's tuctoria, Unit 3 for hairy Orcutt grass, Unit 3 for Hoover's spurge, and Unit 2 for Conservancy fairy shrimp. Other important vernal pool and associated upland species found in the unit include pappose spikeweed, Fremont's goldfields, alkali goldfields, Scribe's popcorn flower, Hoover's downingia, folded downingia, Heckard's peppergrass, heartscale, brittlescale, San Joaquin spearscale, Ferris' milk-vetch, spike-primrose, sessile mousetail, and palmate-bracted bird's beak.

Unit 6, Dolan Unit, Glenn and Colusa Counties (526 ha (1,299 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it contains the primary constituent elements necessary for the conservation of the species and supports occurrences of the species (Holland 1998, Silveira 2000, CNDDB 2001). Vernal pool tadpole shrimp within this unit live within Northern Claypan vernal pools, as defined by Sawyer and Keeler-Wolf (1995). These vernal pools occur on alkaline soils and typically form alkali playas which are larger and contain a more diverse species composition than the hardpan pools further south (Keeler-Wolf et al. 1998). They may display white salt deposits following pool drying.

This unit is primarily located on the Dolan Ranch Conservation bank. This area supports a number of rare alkaline species, and contains remnants of the widespread Colusa Plains vegetation that once covered the entire Colusa Basin (Silveira 2000). Vernal pool habitats on Dolan Ranch are specifically managed for the conservation of listed species. Vernal pool habitats within the area have become greatly fragmented and isolated from other habitats in the region due to urban and agricultural land conversions. This unit occurs east of Interstate 5 and the Sacramento River, south of the City of Colusa, and west of the Colusa National Wildlife Refuge. All the lands within this unit are privately owned.

Unit 7, Beale Unit, Yuba and Placer Counties (2,853 ha (7,049 ac))

The Beale Unit is proposed as essential because it contains vernal pool tadpole shrimp occurrences within large vernal pool complexes that maintain the primary constituent elements essential for the conservation of the species (Holland 1998, CNDDB 2001, Jones and Stokes 2002). Vernal pool tadpole shrimp within the Beale Unit live within large, relatively undisturbed vernal pool grassland habitats and a diversity of vernal pool habitat types. Beale Air Force Base contains 8,000 ha (19,800 ac) of vernal pool grasslands occurring on four major geologic formations: the Modesto Formation; the Riverbank Formation; the Laguna Formation; and the Mehrten Formation. Different geologic formations provide a diversity of habitats for vernal pool tadpole shrimp primarily through their effects on pool size and depth (Platenkamp 1998, Helm 1998). King (1996) found that vernal pool tadpole shrimp within this unit were genetically different than occurrences in other portions of the species range, particularly those on the floor of the Central Valley. This unit is also designated to ensure that special management actions are taken to protect vernal pool habitats within the unit, including vernal pools created and restored throughout the unit which require long-term monitoring and management to ensure they continue to function as viable vernal pools. This unit is also important to maintain an opportunity for long distance dispersal of vernal pool tadpole shrimp cysts the nearest unit to the north is over 45 km (28 mi), and the nearest unit to the south is over 65 km (40 mi) away.

This unit contains DOD land (2,006 ha (5,016 ac) at Beale Air Force Base and 5 ha (13 ac) of BLM land. Other lands within this unit are located on private property. Remaining vernal pool habitats in this unit are threatened by agricultural conversion and by urban expansion. Vernal pool habitats in this area are also threatened by the expansion of Highway 70 and other transportation projects planned in the region.

The Beale Unit is located in southwestern Yuba County, south of the Yuba River and Yuba Goldfields, east of State Route 70, and north of the Bear River. The northwestern boundary of the unit borders the City of Marysville. Other rare vernal pool species found in this unit include vernal pool fairy shrimp, California linderiella, legenere, and dwarf downingia.

Unit 8, Mather Unit, Sacramento County (14,866 ha (36,733 ac))

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains 15 percent of all known occurrences of the species (CNDDB 2001) and vernal pools, swales, and other ephemeral wetlands and depressions mapped by Sacramento County (1999) and Holland (1998) of appropriate sizes and depths for vernal pool tadpole to complete their life cycle. These areas have been identified by the Sacramento Valley Open Space Conservancy, the CNPS, and TNC as excellent examples of vernal pool grasslands, supporting a rich and diverse community of vernal pool endemic plants and animals including vernal pool tadpole shrimp.

This unit supports vernal pool tadpole shrimp occurrences within a diversity of vernal pool habitats, including young or low terrace vernal pools on the Riverbank Formation, old or high terrace vernal pools on the Laguna and Arroyo Seco geologic formations, and Northern Volcanic Mudflow vernal pools on the Mehrten and Valley Springs geologic formations. This unit is one of the few remaining areas where vernal pool tadpole shrimp occur on low terrace landforms on the eastern side of the Central Valley, and is important to maintain a diversity of habitats for the species. The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool tadpole shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp to hatch, mature, and produce cysts.

This unit includes several conservation areas established by private entities, including the Sunrise Douglas Conservation Bank, the Arroyo Seco Conservation Bank, the Churchill Downs mitigation area, and Teichert mitigation areas. These areas were established specifically to contribute to the conservation of vernal pool tadpole shrimp, and represent compensation measures for the loss of thousands of acres of vernal pool tadpole shrimp habitat within Sacramento County. The continued functioning of these areas is essential to the conservation of vernal pool tadpole shrimp and other vernal pool species. This unit contains areas on private, county, and Federal land, including lands leased or owned by Sacramento County at Mather Regional Park, the former Mather Air Force Base, and at the county landfill. Approximately 6 ha (16 ac) within this unit are BLM lands. Vernal pool habitats in this unit are threatened by urbanization from the expanding cities of Sacramento and Elk Grove. Conversion to intensive agriculture, particularly vineyards, is also a significant threat to vernal pool tadpole shrimp in this unit.

This unit includes areas to the east and south of the cities of Sacramento and Elk Grove in Sacramento County. The Cosumnes River forms part of the southwestern boundary of the unit and State Highway 16 lies just south of the southeastern boundary of the unit. The northern boundary is south of State Highway 50 and the American River. The eastern boundary of this unit lies just west of Latrobe Road. The unit is bisected by the Folsom South Canal. This unit also represents Unit 13 for vernal pool fairy shrimp, and contains Unit 6 for slender Orcutt grass and Unit 2 for the Sacramento Orcutt grass. In addition to vernal pool tadpole shrimp, this unit contains occurrences of many other rare endemic vernal pool species including midvalley fairy shrimp, legenere, Bogg's Lake hedge-hyssop, Ahart's dwarf rush, western spadefoot toad, and California linderiella.

Unit 9, Cosumnes Unit, Sacramento, Amador, and San Joaquin Counties (29,063 ha (71,813 ac))

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains the primary constituent elements necessary for the species survival, including over 30 percent of the remaining vernal pool habitats in the southern Sacramento Valley area (Holland 1998, Sacramento County 1999). These habitats provide the necessary timing, length, and frequency of inundation necessary for the survival of vernal pool tadpole shrimp, and this unit supports numerous occurrences of the species (CNDDB 2001). Vernal pool tadpole shrimp within this unit occur on a diversity of pool types, including Northern Volcanic Mudflow vernal pools on the Mehrten and Valley Springs geologic formation overlain by Pardee and Pentz soils, vernal pools occurring on low terrace landforms associated with San Joaquin soils, and high terrace landforms associated with Redding and Corning soils (USDA 2001). King (1996) found that vernal pool tadpole shrimp within this unit were genetically most similar to occurrences in Stanislaus County and nearby in Sacramento County. However, vernal pool tadpole shrimp within this unit were generally different from occurrences at other sites sampled throughout the species range, and were very different from vernal pool tadpole shrimp sampled at sites found further to the west on the floor of the Central Valley, for example at Jepson Prairie or Kesterson National Wildlife Refuge (King 1996).

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where vernal pool tadpole shrimp occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp to complete their life cycles.

This unit contains state and federally owned land, as well as private properties. Portions of the Cosumnes River Preserve occur within this unit. The Cosumnes River Preserve is jointly owned and managed by a variety of state, local, and Federal agencies including the BLM , CDFG, Ducks Unlimited, Inc., California Department of Water Resources, Sacramento Co. Dept. of Regional Parks, Open Space, and Recreation, TNC, and the Wildlife Conservation Board. The Cosumnes River Preserve encompasses and protects thousands of acres of wetlands and adjacent uplands, oak woodlands, and riparian forests along the Cosumnes River, the only undammed river on the west slope of the Sierra. The Cosumnes floodplain is a haven for tens of thousands of migratory waterfowl, songbirds, and raptors, for a large portion of the Central Valley's population of greater sandhill cranes, and for rare reptiles and mammals like the endangered giant garter snake and the river otter. These areas provide habitat for migratory waterfowl and other avian species that aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts.

Several large, diverse, vernal pool landscapes are protected within this unit including the Howard Ranch, and Valensin Ranch. The Clay Station Mitigation Bank, Laguna Creek Mitigation Bank, and the Borden Ranch Mitigation site are included in this unit, as well as a number of smaller conservation areas including the Rancho Seco Preserve. The conservation areas contained within this unit have been established specifically to contribute to the survival of vernal pool tadpole shrimp, and to compensate for the loss of thousands of acres of vernal pool grassland habitats throughout the Southeastern Sacramento Valley vernal pool region. This area has been identified by the Sacramento Valley Open Space Conservancy, the CNPS, and TNC as an excellent example of vernal pool grasslands, supporting a rich and diverse community of vernal pool endemic plants and animals within Sacramento County. Land ownership and protection within the unit includes CDFG (630 ha (1,557 ac)), TNC (3,988 ha (9.970 ac)) lands and WRP easements (4 ha (11 ac)). Vernal pool habitats in this unit are threatened by urbanization from the expanding cities of Sacramento and Elk Grove. Conversion from grazing to other agricultural practices, particularly vineyards, is also a significant threat to vernal pool tadpole shrimp in this unit.

This unit occupies the area south of Deer Creek and the Cosumnes River to just south of the Sacramento and San Joaquin County line near Liberty and Collier roads. The eastern boundary is the low elevation foothills of western Amador County. The western limit is the Sacramento River. This unit also coincides with Unit 19 for vernal pool fairy shrimp, and incorporates Unit 1 for succulent owl's-clover, and Unit 3 for Sacramento Orcutt grass. Other sensitive species found within this unit include Bogg's Lake hedge-hyssop, Ahart's dwarf rush, Henderson's bent grass, legenere, Sanford's arrowhead, pincushion navarretia, dwarf downingia, California tiger salamander, western spadefoot toad, and California linderiella.

Unit 10, Davis Communications Annex Unit, Yolo County (192 ha (474 ac))

This unit is proposed as critical based on the presence of vernal pool tadpole shrimp (CNDDB 2001) and vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool tadpole shrimp incubation, reproduction, dispersal, feeding, and sheltering, but which are dry during the summer and do not necessarily fill with water every year (Yolo County 1995, Holland 1998, Yolo County Parks 2001). Vernal pool tadpole shrimp within this unit are found on claypan type vernal pools. These pools are generally larger and stay inundated for relatively longer periods than vernal pools on alluvial terraces or volcanic mudflows and lava flows. This unit contains DOD (128 ha (321 ac)) and county owned land. Vernal pool habitats in this unit are currently the focus of conservation planning efforts by Yolo County (Yolo County Parks 2001).

This unit coincides with Unit 2 for Colusa grass and Unit 1 for Solano grass. Other rare and special status species that occur in this unit are Baker's navarretia, western spadefoot toad, California tiger salamander, brittlescale, San Joaquin saltbrush, alkali milk-vetch, palmate-bracted bird's beak, and the Heckard's pepper grass.

Unit 11, Jepson Prairie Unit, Solano County (34,610 ha (85,521 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it includes one of the largest contiguous areas of habitat remaining for the species (Holland 1998, Solano County 2000, Solano County Farmlands and Open Space 2000, CNDDB 2001). Vernal pool tadpole shrimp at Jepson Prairie occur in large, playa-like vernal pools which may be over several acres in size, including the 32 ha (80 ac) Olcott Lake. The species can also be found in smaller pools and hogwallow depressions that also occur within this unit. The Jepson Prairie area supports vernal pool tadpole shrimp within unusual combinations of low terrace and basin rim landform vernal pools on a diversity of soil types, maintaining a diversity of habitats for vernal pool tadpole shrimp.

The relatively undisturbed, hydrologically intact condition of the Jepson Prairie increases the likelihood that it will continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for vernal pool tadpole shrimp. This unit also provides habitat for migratory waterfowl that aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts. King (1996) found that vernal pool tadpole shrimp within this unit were genetically distinct from sampled occurrences in other portions of the species' range, including those just a few miles to the east in Sacramento County.

Jepson Prairie has long been recognized as an outstanding example of vernal pool ecosystems. In 1987, the NPS named Jepson Prairie a National Natural Landmark, a designation given to sites that provide high quality habitat for threatened or endangered species. Jepson Prairie is the target of ongoing conservation planning efforts and active management. As part of the UC Reserve System, this area also provides critical research opportunities for scientists to study vernal pool species, including vernal pool tadpole shrimp.

The unit contains lands totaling 2,248 ha (901 ac) owned and approximately 64 ha (160 ac) administered by CDFG. Additional lands are owned by DOD (760 ha (1,879 ac)), California State Parks (15 ha (38 ac)), and the State Land Commission (109 ha (273 ac)). TNC has a conservation easement on 623 ha (1,558 ac) within this unit, and NRCS holds WRP conservation easements or agreements for 436 ha (1,090 ac). The Jepson Prairie Preserve is jointly managed by the Solano Land Trust and the UC Reserve System. Vernal pool tadpole shrimp on private land within this unit are threatened by agricultural conversion, range improvement programs, landfill expansion, power plant construction, and utility maintenance.

This unit is located in the southern portion of Solano County, southeast of Interstate 80 and the cities of Fairfield and Vacaville, north of Grizzly Bay and Montezuma Slough, west of the Sacramento River and the Solano and Sacramento county line, and south of Midway Road and the City of Dixon. The unit is bisected by Highway 13 and Highway 12. This unit is also described as Unit 16 for vernal pool fairy shrimp. This unit contains Unit 3 for Colusa grass, Unit 2 for Solano grass, Unit 3 for Conservancy fairy shrimp, and Unit 4 and portions of Unit 5 for Contra Costa goldfields. Other rare vernal pool species which occur in this unit include alkali milk-vetch, Ferris's milk-vetch, vernal pool small scale, dwarf downingia, Delta green ground beetle, Bogg's Lake hedge-hyssop, Ricksecker's water scavenger beetle, California linderiella, midvalley fairy shrimp, legenere, and California tiger salamander.

Unit 12, Suisun Marsh Area Unit, Solano County (603 ha (1,490 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it contains vernal pools that support the necessary timing, frequency, and duration of inundation essential for vernal pool tadpole shrimp life history requirements including feeding, sheltering, reproducing, and dispersing (Levine Fricke 2000, CNDDB 2001). This unit is one of only two areas where vernal pool tadpole shrimp occur in the saline-alkaline transition zone between vernal pools and tidal marshes, and helps to maintain a diversity of habitat types for this species. All of the habitats within this unit are on private land. The primary threats to vernal pool habitats within this unit are alterations to hydrology from filling, diking, and dredging activities which may occur in the tidal marsh.

This unit is located near the Suisun Marsh in southern Solano County, east of Montezuma Slough and west of Collinsville Road; the northernmost portion of this unit is bisected by Birds Landings Road. Portions of this unit coincide with Unit 4 for Conservancy fairy shrimp. This unit also contains occurrences of other rare vernal pool species including alkali milk-vetch and dwarf downingia.

Unit 13, Stanislaus Unit, Stanislaus, Tuolumne, Mariposa, and Merced Counties (9,408 ha (23,246 ac)

This unit is proposed as critical for vernal pool tadpole shrimp because it contains hardpan pools that occur on soils of alluvial fans and terraces of appropriate sizes and depths that become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool tadpole shrimp incubation, reproduction, dispersal, feeding, and sheltering, but which are dry during the summer and do not necessarily fill with water every year (Holland 1998, CNDDB 2001). Vernal pool tadpole shrimp in this unit occur within numerous small pools and swales on mima mound topography, supported by soils that are typically older than those of the alluvial terraces in the Sacramento area. This unit contains almost 25 percent of vernal pool habitats found along the eastern margin of the San Joaquin Valley. King (1996) found that vernal pool tadpole shrimp within this unit, although similar to vernal pool tadpole shrimp in eastern Sacramento County, were genetically different from other tadpole shrimp occurrences sampled throughout the species' range, particularly those on the floor of the Central Valley.

The Stanislaus Unit contains very high quality, hydrologically intact vernal pool complexes. The well-known Hickman pools in Stanislaus County are located within this unit. Not only does the Hickman pool complex contain one of the largest vernal lakes in California at more than 121 ha (300 ac), but it also exhibits tremendous biodiversity, including one of the largest concentrations of imperiled amphibians (Medeiros 2000). However, the watershed containing the Hickman vernal pools has been breached by hundreds of acres of orchards that have been planted upstream. While most of the watershed has been managed over the years in a trust of the Fred Robinson family, the integrity of the vernal pool ecosystem is threatened by agricultural development and potential biocide pollution (Medeiros 2000).

The Stanislaus Unit is bordered by the Stanislaus River to the north and Dry Creek to the south and southeast. This unit coincides with vernal pool fairy shrimp Unit 22. It also encompasses succulent owl's-clover units 3 and 4, San Joaquin Valley Orcutt grass units 1 and 2, hairy Orcutt grass units 4 and 5, Colusa grass units 5 and 6, Hoover's spurge units 4 and 5, Greene's tuctoria units 8 and 9, and Conservancy fairy shrimp units 4 and 6. Other sensitive vernal pool species found within this unit include western spadefoot toad, dwarf downingia, California linderiella, California tiger salamander, and Hartweg's golden sunburst. All the land within this unit is privately owned.

Unit 14, San Francisco Bay Unit, Alameda and Santa Clara Counties (458 ha (1,132 ac)

This unit is proposed as critical habitat for vernal pool tadpole shrimp because it contains occurrences of the species living within vernal pools that are inundated for sufficient periods of time for vernal pool tadpole shrimp hatching, growth, and reproduction, but are dry during the summer to prevent the establishment of aquatic predators such as bullfrogs and fish (Holland 1998, CNDDB 2001). The unit boundary was identified based on the distribution of vernal pool tadpole shrimp and the presence of these primary constituent elements, including vernal pools mapped by Holland (1998) and vernal pool areas delineated by Wetlands Research Associates (1999). The southern and western boundaries were delineated to exclude estuarine habitats and urban areas visible on SPOT imagery. This unit is also designated so that special management actions will be taken within vernal pool creation areas occurring within this unit. These areas have been created specifically to contribute to the conservation of vernal pool tadpole shrimp. Monitoring and management of these created pools will be necessary to ensure their continued suitability for vernal pool tadpole shrimp. We own approximately 10 ha (24 ac) within this unit.

This area represents the only location where vernal pool tadpole shrimp occur in the San Francisco Bay region. Vernal pool tadpole shrimp within this unit are found in a unique tidal marsh estuary area that represents an unusual habitat type for the species. This unit represents the western extent of the species range, and is disjunct from other vernal pool tadpole shrimp populations elsewhere within the species' range in central California. This unit is over 60 km (37 mi) from the nearest unit to the north, and over 90 km (56 mi) from the nearest units to the east and south. Peripheral populations such as these may have genetic characteristics essential to overall long-term conservation of the species (i.e., they may be genetically different than more central populations) (Lesica and Allendorf 1995).

This unit is situated south of the cities of Fremont and Newark, west of Interstate 880 and north of Mud Slough. This unit is a portion of Unit 8B for Contra Costa goldfields. Portions of this unit occur within the boundaries of San Francisco Bay National Wildlife Refuge. This unit includes a preserve established as conservation measures for vernal pool tadpole shrimp as part of the Pacific Commons development project (Service 2000b). This subunit also supports a large population of the California tiger salamander.

Unit 15, Merced Unit, Merced and Mariposa Counties (71,076 ha (175,626 ac)

This unit is proposed as critical for vernal pool tadpole shrimp because it contains more documented occurrences of the species than any other area throughout the species range (CNDDB 2001). The vernal pool tadpole shrimp in this area occur in the largest block of pristine, high density vernal pool grasslands remaining in California (Vollmar 1999). These vernal pools provide the primary constituent elements essential for the conservation of vernal pool tadpole shrimp, and supports multiple large vernal pool tadpole shrimp occurrences that are capable of producing large numbers of cysts in good years, which is important for this species to survive through a variety of natural and environmental changes, as well as stochastic (random) events. The Merced Unit contains almost 15 percent of all remaining vernal pool habitats in the Central Valley, and 40 percent of vernal pool habitats along the eastern margin of the San Joaquin Valley (Holland 1998). Genetic analyses of vernal pool tadpole shrimp revealed that occurrences in this unit are genetically different from other sampled occurrences (King 1996). Of all occurrences studied, King (1996) found these to be the most highly divergent.

The integrity of the vernal pool complexes in eastern Merced is seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced Campus and associated development. Construction of facilities to educate and serve twenty-five thousand UC students as well as faculty, staff, and their families within the vernal pool complexes in eastern Merced County, could have a major impact on vernal pool tadpole shrimp occurrences. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Indirect and cumulative impacts of the proposed 1,673 ha (4,133 ac) campus and associated community may be minimized with the creation of a 2,036 ha (5,030 ac) preserve intended to protect sensitive vernal pool habitat, to be purchased with money donated by the Packard Foundation. Land ownership within the unit includes approximately 3 ha (8 ac) of BLM, and 11 ha (26 ac) of California State Parks. TNC has a total of 4,513 ha (11,283 ac) of conservation easements within this unit.

A majority of the vernal pool habitat in the Merced Unit is in Merced County. The eastern edge of the unit generally follows the Mariposa County line. The Chowchilla River in Madera County flows along the southern boundary of the unit. The northern boundary parallels the Merced River. The entire unit is located east of Highway 99. The Merced Unit coincides with vernal pool fairy shrimp Unit 22, succulent owl's-clover units 3B, Greene's tuctoria Unit 6, Conservancy fairy shrimp Unit 6, Colusa grass Unit 7, San Joaquin Valley Orcutt grass units 2 and 3. Other sensitive vernal pool species found within this unit include the California tiger salamander, shining navarretia, dwarf downingia, Bogg's Lake hedge-hyssop, western spadefoot toad, California linderiella, and spiny-sepaled button celery (Eryngium spinosepalum).

Unit 16, Grassland Ecological Unit, Madera, Merced and Stanislaus Counties (55,910 ha (138,153 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it supports seven percent of the known occurrences of the species (CNDDB 2001) within large vernal pool complexes mapped by Holland (1998). This is the only area where vernal pool tadpole shrimp occur on the floor of the San Joaquin Valley, and contains over 50 percent of the remaining vernal pool habitats within this region (Holland 1998). Vernal pool tadpole shrimp within this unit occur on Northern Claypan vernal pools formed by a diversity of vernal pool soil types, including Delhi-Dello-Himar, Solano-Caypay-Willows, Rossi-Waukena, and Lewis-Landlow soils (Silveira 2000). Many of the vernal pools supporting vernal pool tadpole shrimp within this unit are large (over several acres in size), turbid, and alkaline. All of these pool types provide the necessary timing and length of inundation for vernal pool tadpole shrimp hatching, growth, and reproduction.

This unit boundary was drawn to include the large, intact vernal pool grasslands supporting hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands where vernal pool tadpole shrimp are known, as mapped by Holland (1998) and as visible on SPOT imagery. However, the 16-ha (40-ac) minimum mapping unit of Holland (1998), and the resolution of SPOT imagery, did not allow us to exclude all agricultural areas from within this unit. These features, which comprise the vernal pool complex, contribute to the filling and drying of the vernal pools, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool tadpole shrimp hatching, growth and reproduction, and dispersal. This unit also provides essential habitat for migratory waterfowl that aid in the dispersal of vernal pool tadpole shrimp and other vernal pool crustacean cysts. King (1996) found that vernal pool tadpole shrimp occurrences within this unit, although most similar to occurrences at Sequoia Field in Tulare County, are genetically different from other vernal pool tadpole shrimp throughout the species range. The vernal pool tadpole shrimp in this unit genetically very different from sampled occurrences less than 12 km (7 mi) to the east in the foothills of the Sierra Nevada.

The Grassland Ecological Unit includes Kesterson, San Luis, and Merced National Wildlife Refuges (13,943 ha (34, 452 ac)), CDFG lands (1,703 ha (4,257 ac)), CDFG administration lands (1,052 ha (2,631 ac)), California State Parks (1,358 ha (3,392 ac)), and WRP easements (54 ha (134 ac)). Together, these areas are known as the Grasslands Ecological Area. This area supports diverse wetland habitats including seasonally flooded marshlands, semi-permanent marsh, riparian habitat, wet meadows, vernal pools, native uplands, pastures, and native grasslands. Wetlands within this area, including seasonal marsh and open water habitats, constitute 30 percent of the remaining wetlands in California's Central Valley and are extremely important to Pacific Flyway waterfowl populations. Over 60 million duck use-day and 3 million goose use-days occur annually in this unit. This habitat also supports a diversity of other migratory birds, including raptors, shorebirds, wading birds, and other wildlife species.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit overlaps Unit 23 for vernal pool fairy shrimp and Unit 7 for Conservancy fairy shrimp. The western half of this unit also represents Unit 2 for longhorn fairy shrimp, and the eastern half represents Unit 8 for Colusa grass, and Unit 6 for Hoover's spurge. In addition to the species mentioned above, vernal pool smallscale, alkali milk-vetch, western spadefoot toad, and California linderiella are other special status vernal pool species present in this unit.

Unit 17, Table Mountain Unit, Fresno County (740 ha (1,829 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it supports occurrences of vernal pool tadpole shrimp (CNDDB 2001) and extensive vernal pool complexes (Holland 1998, Keeler-Wolf et al. 1998). The unit also contains Northern Basalt Flow vernal pools that provide the necessary timing, frequency, and length of inundation necessary for the species to hatch, mature, reproduce, and complete its life cycle. The basalt flow vernal pools within this unit are found on narrow, sinuous basalt mesas above the surrounding low-lying terrain. Basalt flow vernal pools are a very rare habitat type for vernal pool tadpole shrimp and the habitats within this unit are important for maintaining the range of ecological conditions in which the species occurs. They typically contain small, irregularly clustered pools with “flashy hydrology” (Keeler-Wolf et al. 1998). The occurrences of vernal pool tadpole shrimp in this unit are genetically different from occurrences in other portions of the species range, particularly those occurring on the floor of the Central Valley (King 1996). Big Table Mountain, an ancient basalt mesa near Millerton Lake, is found within this unit and is owned and managed by CDFG, TNC, BLM. Land ownership within the unit includes BLM (84 ha (209 ac)), CDFG lands (172 ha (430 ac)), and TNC conservation easements (256 ha (639 ac)). All other lands within this unit are privately owned.

Located in Fresno County, this unit contains vernal pool habitats east and south of the San Joaquin River and east of Millerton Lake. The unit is west of Marshall Station and North of Table Mountain Rancheria. This unit coincides with succulent owl's-clover Unit 6A and San Joaquin Valley Orcutt grass Unit 6B. Other sensitive vernal pool species found within this unit include the Bogg's Lake hedge-hyssop, Molestan blister beetle (Lytta molesta), California linderiella, California tiger salamander, and the western spadefoot toad.

Unit 18 A, B and C, Tulare Unit, Tulare County (3,193 ha (7,890 ac))

This unit is proposed as critical for vernal pool tadpole shrimp because it supports occurrences of the species (CNDDB 2001) within vernal pools that provide the essential primary constituent elements essential for vernal pool tadpole shrimp conservation (Holland 1998). The unit boundary was delineated to include vernal pool tadpole shrimp occurrences (CNDDB 2001) and the vernal pool complexes in which they occur (Holland 1998). However, the 16-ha (40-ac) minimum mapping unit of Holland (1998), and the resolution of SPOT imagery, did not allow us to exclude all agricultural or developed areas from within this unit. Vernal pool tadpole shrimp in this area are found within pools formed on San Joaquin, Cometa, and Madera soils, among others. This unit represents the southern extent of vernal pool tadpole shrimp's range. The Sequoia Field occurrence was most closely related to occurrences at Kesterson National Wildlife Refuge, and was generally more similar to other occurrences on the valley floor than occurrences found on the eastern margin of the valley in the Sierra Nevada Foothills. However, King (1996) found that vernal pool tadpole shrimp within this unit were genetically different from other populations studied.

These pools are the focus of ongoing conservation efforts by CDFG, who manage vernal pool habitats at the Stone Corral and Sequoia Field Ecological Reserves found within this unit. Keeler-Wolf et al. (1998) identified the vernal pools in these areas as “high quality hardpan pools.” Much of the area within this unit is owned by CDFG (348 ha 861 ac)) or occurs on private land. Agricultural conversion of range or barren land, particularly for orchards and feed lots, as well as residential and commercial development, have greatly reduced the amount of vernal pool habitat in Tulare County and threatens remaining habitats on private land in this unit.

This unit is comprised of three subunits. Subunit A is located in northwest Tulare County and contains vernal pool habitat located west of Seville. The Friant Kern Canal is north of the unit and the Cottonwood Creek Levee is south of the unit. Road 140 runs west of the unit. Subunit B contains vernal pools in northeastern Kings County and northwestern Tulare County. Highway 99 and St. Johns River cut through the unit in a southeasterly direction. Cross Creek and Cottonwood Creek cut through the unit in a southwesterly direction. Road 112 is east of the unit and the Lakeland Canal is west of the unit. The towns of Goshen and Visalia are south of the unit and Traver and London are north of the unit. Subunit C is known as Sequoia Field Unit and is located in northwestern Tulare County. This unit is south of County Road J36. Road 112 crosses through the western edge of the unit, Avenue 352 crosses through the southern edge, and State Route 63 crosses through the eastern edge. The Cross Creek Unit coincides with vernal pool fairy shrimp Unit 26 and contains portions of San Joaquin Valley Orcutt grass Unit 8 and Hoover's spurge Unit 9. Other sensitive vernal pool species found within this unit include the California tiger salamander, spiny-sepaled button-celery, and western spadefoot toad.

Butte County Meadowfoam

In proposing critical habitat units for Butte County meadowfoam, we evaluated the life history and current distribution of the species, the primary constituent elements, the threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of these species and to delineate units so that threats to this species might be minimized.

Butte County meadowfoam is restricted to a single county in California. The species is only known from 11 extant occurrences. An additional two occurrences are considered extirpated. Butte County meadowfoam is found in four centers of concentration. One center of concentration is the Shippee Road area between Chico and Oroville, while the other three centers of concentration are in the vicinity of the City of Chico.

An important consideration for designating Butte County meadowfoam critical habitat is to minimize the threat of habitat fragmentation. All of the Chico area populations have been fragmented by the construction of roads or canals; several of the now separate occurrences may well have been continuous in the past. The roads and canals also altered the drainage patterns at many sites, reducing their suitability for Butte County meadowfoam by creating conditions too dry or too wet for its survival (Dole 1988, Jokerst 1989, Kelley and Associates Environmental Sciences 1992). Although some plants still remained at the type locality as of 1989, the site had been severely degraded by grading, agricultural use, and off-road vehicles (Jokerst 1989, Dole and Sun 1992, 2000). Several populations have been reduced in size by surface disturbances such as grading and removal of topsoil (Jokerst 1989, Service 1992a).

Another important criterion is that critical habitat units minimize the potential for alterations in hydrology. Changes in hydrology throughout the range of Butte County meadowfoam are possible from developments adjacent to extant populations, from further construction of roads and canals, and from grading or other surface disturbances. Moreover, subtle hydrological changes that already have taken place are likely to continue reducing Butte County meadowfoam, leading to the eventual extirpation of populations such as one occurrence north of the Chico Municipal Airport.

Special management actions may be necessary in some areas to promote occurrences of Butte County meadowfoam. Light grazing may help to control competing plant species and prevent thatch accumulation (Jokerst 1989). Competition from medusa head (Taeniatherum caput-medusae) apparently has reduced population size and seed set in Butte County meadowfoam at the Doe Mill Preserve (Center for Natural Lands Management 1997), and invasion of grasses and other weedy non-native plants poses a potential problem at three other occurrences (CNDDB 2002) including the occurrence at the Chico airport and an occurrence in the southern portion of the species range near Shippee Road.

Butte County Meadowfoam Unit Review

We conducted a regional review across the range of Butte County meadowfoam to evaluate and select vernal pool habitats that are essential to the conservation of the species and may require special management. Important factors we considered were the known presence of Butte County meadowfoam and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Rock Creek Unit, Butte, and Tehama Counties (6,105 ha (15,086 ac))

This unit is proposed as critical for Butte County meadowfoam because it contains the species identified by CNDDB (2002) within vernal pools, swales, and complexes mapped by Holland (1998) and the EPA (1994). These habitats contain the primary constituent elements necessary for the species survival and long-term conservation, including vernal pools on the Tuscan formation, which typically contain water for shorter periods of time than other types of vernal pools.

This unit represents the northern extent of Butte County meadowfoam's range, and includes occurrences from the northern race of Butte County meadowfoam. This race is genetically different from the southern race (Jokerst 1989, Dole and Sun 1992), and is important to maintain genetic diversity within the species. An introduced occurrence also occurs within this unit, although this occurrence represents individuals thought to be of the southern race. This unit represents one of only four areas where Butte County meadowfoam occurs throughout its entire range. Each unit is likely important to allow the species to tolerate natural and environmental changes, as well as random (stochastic) events.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and to maintain suitable periods of pool inundation, water quality, and soil moisture for Butte County meadowfoam germination and reproduction. The majority of the lands included within this unit are privately owned. Urban development, agricultural conversion, and hydrologic disruptions or modifications have greatly disturbed vernal pool habitats and restricted Butte County meadowfoam's distribution in this unit.

This unit for Butte County meadowfoam occupies an area north of the City of Chico and includes vernal pool habitats east of Highway 99 along the Sierra foothills from near Pine Creek southeast to Rock Creek. This unit overlaps Unit 1 for Conservancy fairy shrimp, Unit 7 for vernal pool fairy shrimp, and Unit 3 for vernal pool tadpole shrimp. All the lands within this unit are privately owned.

Unit 2, Chico Unit, Butte County (3,508 ha (8,667 ac))

This unit is proposed as critical for Butte County meadowfoam because the species is present and represents a large portion of the species range (CNDDB 2002). Vernal pools and swales that have the primary constituent elements necessary for the conservation of Butte County meadowfoam occur throughout this unit, including vernal pool habitats on Tuscan-Anita soils and the Tuscan, Riverbank, Redbluff, and Modesto geologic formations (EPA 1994, Holland 1998, Liss 2001, CNDDB 2001). This unit contains individuals from the northern race of the species, which is genetically different from the southern race (Jokerst 1989, Dole and Sun 1992) and is important to maintain the species genetic diversity. This unit is also designated so that special management actions, such as grazing, will be taken to reduce the negative effects of invasion of non-natives on occurrences of Butte County meadowfoam. This unit is one of only four units for Butte County meadowfoam across its entire range. Each unit is important to allow the species to tolerate a variety of natural and environmental changes, as well as random (stochastic) events.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Butte County meadowfoam germination and reproduction. The majority of the lands included within this unit are privately owned. Portions of the Chico County Airport are included within this unit. A protected area has been set up at Foothill Park. Urban development, agricultural conversion, and hydrologic disruptions or modifications have greatly disturbed vernal pool habitats and reduced Butte County meadowfoam's distribution throughout this unit.

This unit for Butte County meadowfoam occupies an area directly northeast and adjacent to the City of Chico. The unit extends south from Rock Creek and the Chico Airport to near Big Chico Creek. Highway 99 is located west of this unit. This unit is within Unit 7 for vernal pool fairy shrimp, and Unit 3 for vernal pool tadpole shrimp. Other sensitive vernal pool species found within this unit include California linderiella and western spadefoot toad.

Unit 3, Doe Mill Unit, Butte County (1,696 ha (4,191 ac))

This unit is proposed as critical for Butte County meadowfoam because the species is found living within vernal pools that provide the necessary timing and duration of inundation for Butte County meadowfoam growth, reproduction, and dispersal, including vernal pools underlain by the Tuscan geologic formation on Igo-Redding soils (EPA 1994, Holland 1998, Liss 2001, CNDDB 2001). This unit is also designated so that special management actions, including grazing or other forms of thatch removal, will be taken to reduce the negative effects of invasion of non-natives on occurrences of Butte County meadowfoam. Plants within this unit are of the southern race of Butte County meadowfoam (Jokerst 1989, Dole and Sun 1992) and comprise a significant portion of the species genetic diversity.

The Doe Mill Preserve (6 ha (15 ac)), managed by the City of Chico, is within this unit. Approximately 8.8 ha (22 ac) are public lands owned by the USFS. The remaining lands within this unit are privately owned. Urban development, agricultural conversion, and hydrologic disruptions or modifications have greatly disturbed vernal pool habitats and Butte County meadowfoam occurrences throughout this unit. The distribution of the species and vernal pool habitats within the Chico area have become highly fragmented and isolated from each other.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools and swales where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Butte Count meadowfoam germination and reproduction. This unit occupies an area directly southeast and adjacent to the City of Chico. This unit is within Unit 9 for vernal pool fairy shrimp, and Unit 4 for vernal pool tadpole shrimp.

Unit 4, Oroville Unit, Butte County (5,011 ha (12,382 ac))

This unit is proposed as critical for Butte County meadowfoam because it contains vernal pools and swales on the Tuscan, Red Bluff and Riverbank geologic formations where the species is found (EPA 1994, Holland 1998, Liss 2001, CNDDB 2001). This unit contains individuals from the southern race of Butte County meadowfoam and represents an important component of the species genetic diversity. This unit also represents the southern extent of Butte County meadowfoam's range. The “Shipee Site” has been described as the type locality for the species and is located within this unit. This unit is also designated so that special management actions, such as grazing, will be taken to reduce the negative effects of invasion of non-natives on occurrences of Butte County meadowfoam. This unit represents one of only four units for Butte County meadowfoam across its entire range. All four of these units are essential for the species to endure through a variety of natural and environmental changes, as well as random (stochastic) events.

The lands included within this unit are privately owned. Urban development, highway expansion and construction, agricultural conversion, and hydrologic disruptions or modifications have greatly impacted vernal pool habitats and restricted Butte County meadowfoam's distribution throughout this unit. The distribution of the species and vernal pool habitats within the Chico area have become highly fragmented and isolated from each other.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Butte County meadowfoam germination and reproduction. This unit occupies an area northwest of the City of Oroville. The unit is located south of Dry Creek near State Route 70 southeast to the Thermalito Diversion Pool. This unit is within Unit 4 for vernal pool tadpole shrimp, and encompasses part of Unit 5 for Greene's tuctoria.

Contra Costa Goldfields

In proposing critical habitat units for Contra Costa goldfields, we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are essential to the conservation of this species and to delineate units so that threats to this species might be minimized.

Of the 30 occurrences of Contra Costa goldfields that were documented between 1884 and 1999, 19 are probably extant. The uncertainty is due in part to the difficulty of relocating sites based on vague descriptions. In addition, this species may reappear on a site after several years even if it is absent during a given survey. Contra Costa goldfields is known from disjunct locations in the coastal regions of California. By far the greatest concentration of this species is in the area east of Fairfield in Solano County. Additional occurrences are extant at Fort Ord in Monterey County, the San Francisco Bay National Wildlife Refuge and near Fremont in Alameda County, near Rodeo in Contra Costa County, near Manchester in Mendocino County, and at Suscol Ridge and Milliken Canyon in Napa County (CNDDB 2001).

Urban and residential development are believed to be responsible for the loss of at least four Contra Costa goldfields occurrences east of San Francisco Bay. Although the original collection sites cannot be pinpointed from the descriptions given on specimen labels, the areas in question (Antioch, Concord, Newark, San Jose, and Walnut Creek) are highly developed. One site in Fremont (near Newark) was degraded by cultivation and operation of a racetrack, but Contra Costa goldfields reappeared approximately a decade after the fields were abandoned (Baye in litt. 2000a). Urbanization is presumed to have extirpated one or more occurrences near Santa Barbara. One Napa County occurrence was destroyed by conversion to a vineyard. At least four former occurrence sites in Solano County have been degraded by surface disturbances, including discing and creek channelization, which removed some habitat, altered the hydrology, and allowed invasion of non-native, upland plants. Contra Costa goldfields has not grown at three of these sites during the past 10 years (CNDDB 2002).

Urbanization is the greatest threat to Contra Costa goldfields. Except for Travis Air Force Base, the entire concentration area in Solano County is in the Fairfield sphere of influence and is subject to development under the city's general plan. Development also threatens one of the two remaining Alameda County/San Francisco Bay occurrences. Another serious threat is conversion to vineyards. The largest Napa County occurrence, at Suscol Ridge (CNDDB 2001), is threatened by vineyard conversion.

Invasion of non-native plants, particularly Italian ryegrass, threatens at least eight occurrences, several of which are also targeted for development (CNDDB 2001). Encroachment by non-native plants often follows surface-disturbing activities such as discing, grading, filling, and off-road vehicle use, which can alter hydrology and microhabitat conditions. Such surface disturbances are apparent at nine sites, four of which do not yet have reported problems with non-native species (CNDDB 2001). The CNDDB (2001) cites livestock grazing as a threat to seven occurrences. However, grazing may help to control invasion of non-native plants under certain conditions. Contra Costa goldfields persisted through horse grazing on Travis Air Force Base, but several small colonies disappeared when horses were excluded. Even moderately heavy grazing can be compatible with Contra Costa goldfields if it is suspended during critical growth periods. Occurrences of Contra Costa goldfields in the Fort Ord area of Monterey County exist at locations that have or potentially contain ordinance and explosives that are byproducts of military training activities. Efforts at the former military base have been underway to remove and dispose of these items. Clearance of ordinance and explosives may involve selectively removing vegetation, digging to expose buried objects, burning, and clearing of the ground surface. Project personnel have and will continue to implement measures that are designed to minimize and mitigate adverse effects to Contra Costa goldfields as ordinance and explosive removal activities proceed, but a potential exists that some plants and habitat may be affected by the clean up activities.

Contra Costa Goldfields Unit Review

We conducted a regional review across the range of Contra Costa goldfields to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the presence of the species and the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Manchester Unit, Mendocino County (1,067 ha (2,637 ac))

This unit is proposed as critical habitat for Contra Costa goldfields because it contains the last known occurrence of Contra Costa goldfields in Mendocino County and is the northern and western limit of the species range (CNDDB 2002). Vernal pools in which Contra Costa goldfields are found occur on Crispin loam soils, which provide the necessary timing and length of inundation to meet the life history requirements of Contra Costa goldfields. This is also the only location where Contra Costa goldfields is found on this soil type.

This unit represents the only occurrence of Contra Costa goldfields in the Mendocino coast area. This unit is over 140 km (87 mi) from the closest Contra Costa goldfields unit to the south. Peripheral populations such as this may have genetic characteristics essential to the overall long-term conservation of the species (i.e., they may be genetically different from more central populations) (Lesica and Allendorf 1995).

The boundaries of this unit were delineated by using SPOT imagery and elevation contours to include the open flat areas associated with the vernal pool habitat and associated uplands that contribute to the filling and drying of the vernal pools where the Contra Costa goldfields occur. The unit includes area sufficient to maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields to germinate, grow, and reproduce.

This unit is on private land and threats to this unit include conversion to vineyards, erosion, draining, and residential development. This unit is located in the vicinity of the town of Manchester just north of the Garcia River and east of the Pacific Ocean. State Highway 1 bisects this unit and Brushy Creek forms the northern and northeastern boundary of the unit.

Unit 2, Berryessa Unit, Napa County (411 ha (1,016 ac))

This area is proposed as critical habitat for Contra Costa goldfields because the species is found (CNDDB 2002) within rock outcrops pools on soils derived from Rhyolite lava flows, within chaparral ecosystems (Holland 1998, USDA 2001, CNDDB 2002). These pools provide the necessary primary constituent elements essential for the conservation of Contra Costa goldfields. This is the only unit where Contra Costa goldfields occurs on Northern Basalt Flow vernal pools, and this area is important to maintain the range of habitats in which the species is known to occur.

The boundaries of this unit were delineated by using SPOT imagery, elevation contours, and CNDDB (2002) data which identified Northern Basalt Flow vernal pool habitat within the unit. The unit includes the open flat areas associated with the vernal pool habitat and associated uplands that contribute to the filling and drying of the vernal pools where the Contra Costa goldfields occur. The unit includes area sufficient to maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields to germinate, grow, and reproduce.

This unit represents some of the last remaining vernal pool habitats in the north bay foothills, and is the only unit for Contra Costa goldfields in this area. This unit is over 25 km (15 mi) from the nearest Contra Costa goldfields unit.

This unit is located south of Lake Berryessa and lies in the Milliken Canyon area east of the City of Yountville and northeast of the City of Napa. Other sensitive vernal pool species found within this unit include dwarf downingia, and few-flowered navarretia. All the lands within this unit are privately owned.

Unit 3, Napa River Unit, Napa and Sonoma Counties (275 ha (678 ac))

This unit is proposed as critical for Contra Costa goldfields because the species is found within vernal pool habitats that support the primary constituent elements essential to the conservation of Contra Costa goldfields (CNDDB 2002). This unit is located on private land, including the Suscol Ridge area, which is threatened by vineyard conversion. This unit is located directly east of the Napa River adjacent to the salt marsh areas of the lower Napa River. Other rare vernal pool species found in this unit include alkali milk-vetch.

Unit 4, Travis and Fairfield Unit, Solano County (7,885 ha (19,484 ac))

This unit is proposed as essential for the conservation of Contra Costa goldfields because it contains 30 percent of the known occurrences of this species within vernal pools in alkaline and saline-alkaline sites, as well as those on San Ysidro and Antioch soil series (Holland 1998, USDA 2001, Solano County 1999, CNDDB 2002). The unit boundary was delineated to include Contra Costa goldfields occurrences and the vernal pool complexes in which they occur. These complexes contribute to the filling and drying of Contra Costa goldfields habitats, and maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields germination, growth and reproduction, and dispersal, but not necessarily every year. The eastern boundary of this unit was identified by the Elmira watershed boundary to exclude vernal pool habitats in the Jepson Prairie area that are outside the currently known range of Contra Costa goldfields.

This unit is located primarily on private land, but also includes DOD property at Travis Air Force Base (1,931 ha (4,828 ac)), CDFG land (117 ha (292 ac)), and State Land Commission Property (4 ha (9 ac)). Conservation areas have been established for Contra Costa goldfields at Travis Air Force Base, and these occurrences are the subject of on-going research projects addressing the restoration and management of this and other vernal pool species and their habitats. Vernal pool habitats within this unit are threatened by urbanization from the cities of Fairfield and Suisun City, and by large-scale transportation projects, such as Jepson Parkway. The remaining vernal pool habitats within the City of Fairfield and Suisun City are currently the subject of conservation planning efforts by local agencies.

This unit occurs in the southern portion of Solano County, northeast of the City of Fairfield, southwest of the City of Vacaville, and north of the Potrero Hills and Nurse Slough. This unit overlaps with Unit 3 for Conservancy fairy shrimp, and is a portion of Unit 11 for vernal pool tadpole shrimp and Unit 16 for vernal pool fairy shrimp. Other rare vernal pool species which occur in this unit include alkali milk-vetch, legenere, and California tiger salamander.

Unit 5 A and B, Suisun Marsh Area Unit, Solano County (411 ha (1,014 ac))

This unit is proposed as critical habitat for Contra Costa goldfields because it contains occurrences of the species within vernal pools in the saline-alkaline transition zone between vernal pools and tidal marshes on Rincon soil series (USDA 1994, CNDDB 2002). The boundaries of this unit includes the vernal pool complexes mapped by Holland (1998) and the grassland habitats mapped by Solano County (2001) where Contra Costa goldfields occurs (CNDDB 2001). These habitats provide the necessary timing and length of inundation for Contra Costa goldfields germination, maturation, reproduction, and dispersal (CNDDB 2001).

The primary threats to Contra Costa goldfields habitats within this unit are alterations to hydrology from filling, diking, and dredging activities which may occur in the tidal marsh. Most of the habitats within this unit are on private land, although portions of the Hill Slough Wildlife Area managed by the CDFG are also included within this unit. Subunits in the vicinity of Fairfield and Suisun City are also threatened by urbanization.

This unit consists of two subunits in the Suisun Marsh area of southern Solano County. Subunit 5A is the westernmost subunit and is located south and east of the City of Cordelia and the junction of Interstate Highways 80 and 680; this subunit is bisected by the Southern Pacific Railroad line. Subunit 5B is located southwest of the City of Fairfield and west of the City of Suisun City; this subunit is bisected by the Southern Pacific Railroad line. In addition to vernal pool fairy shrimp and vernal pool tadpole shrimp, this unit contains occurrences of other rare vernal pool species including alkali milk-vetch and dwarf downingia.

Unit 6, Rodeo Creek Unit, Contra Costa County (243 ha (599 ac))

This unit is proposed as critical habitat for Contra Costa goldfields because it supports occurrences of the species within vernal pool habitats formed on Conejo clay loam soils (USDA 2001, CNDDB 2002). The unit boundary was delineated to include the features that contribute to the filling and drying of the vernal pools where Contra Costa goldfields occurs, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields' germination, growth and reproduction, and dispersal, but not necessarily every year. It is the only area where the species occurs in the vicinity of the Sacramento-San Joaquin delta. This unit is over 25 km (16 mi) from the closest unit to the north, and almost 50 km (32 mi) from the closest unit to the south.

This unit is situated along Rodeo Creek and adjacent to State Highway 4. The unit lies southeast of the City of Rodeo and northeast of the City of Hercules. The unit contains a 3.94 ha (9.74 ac) conservation easement area established in 1999 to protect three known locations of Contra Costa goldfields along Rodeo Creek from highway construction activities along State Route 4. Other rare species which occur in this unit include the federally threatened California red-legged frog and another sensitive species, the western pond turtle (Clemmys marmorata). All the lands within this unit are privately owned.

Unit 7, Byron Hot Springs Unit, Contra Costa County (1,379 ha (3,406 ac))

This unit is proposed as critical habitat for Contra Costa goldfields because it contains the only remaining extant occurrence of Contra Costa goldfields in southeastern Contra Costa County (CNDDB 2001). This occurrence within vernal pools formed on Linne clay loam soils, and has been characterized as alkaline meadow (USDA 2001, CNDDB 2002). This habitat provides the timing and frequency of inundation essential to the germination, growth, and reproduction of Contra Costa goldfields, and this area includes a unique habitat type for this species. The unit boundary includes vernal pool complexes mapped by Holland (1998) where Contra Costa goldfields is known to occur (CNDDB 2002). This unit is over 35 km (22 mi) from the closest unit to the north, and almost 50 km (32 mi) from the closest unit to the south.

This unit is in the vicinity of Byron Hot Springs and Byron Airport and lies directly west of Clifton Court Forebay. This unit mostly includes habitat in low-lying areas east of Altamont Hills, but also includes habitat within a small portion of Altamont Hills. A small portion of this unit overlaps with Unit 19B for vernal pool fairy shrimp. Approximately 232 ha (581 ac) within this unit are owned by the CDFG and 55 ha (137 ac) are owned by the State Land Commission the rest is privately owned.

Unit 8, Southeastern San Francisco Bay Unit, Alameda and Santa Clara Counties (458 ha (1,132 ac))

This unit is proposed as critical for Contra Costa goldfields because it contains occurrences of this species within vernal pools, swales, moist flats, and other ephemeral wetlands in saline alkaline transition zones with tidal marsh habitats that sustain Contra Costa goldfields germination, growth and reproduction (CNDDB 2002, Holland 1998). The unit boundary was identified based on the distribution of Contra Costa goldfields and the presence of these primary constituent elements, including vernal pools mapped by Holland (1998) and vernal pool areas delineated by Wetland Research Associates (1999). The southern and western boundaries were delineated to exclude estuarine habitats and urban areas visible on SPOT imagery.

This unit contains a 180 ha (450 ac) preserve established specifically to contribute to the recovery of Contra Costa goldfields (Service 2000b, Wetland Research Associates 1999) and 443 ha (1,108 ac) of this unit is owned by the Service. This unit is over 50 km (31 mi) from the nearest units to the north, and almost 100 km (62 mi) from the nearest Contra Costa goldfields unit to the south.

This unit occurs in southeastern San Francisco Bay and also represents Unit 14 for vernal pool tadpole shrimp. The unit lies between the northernmost and southernmost subunits and is situated south of the cities of Fremont and Newark and north of Mud Slough. Portions of this unit is found within the boundaries of San Francisco Bay National Wildlife Refuge and the rest is privately owned.

Unit 9, Fort Ord Unit, Monterey County (3,372 ha (8,331 ac))

The Fort Ord unit includes seasonally flooded pool habitats and mima mound grassland areas that are within the boundary of an area that was previously managed as the Fort Ord Army Base. These lands are now or will be managed by a number of Federal and local governments following a transfer from the DOD. Approximately 2,894 ha (7,234 ac) of this unit are currently owned by the DOD, 437 ha (1,093 ac) by BLM, and 2 ha (4 ac) by Monterey County. The critical habitat unit includes a number of seasonally-flooded wetland habitats and at least four locations that possess Contra Costa goldfields. Monitoring activities at two of the four locations suggest that listed plant numbers vary on an annual basis, and that differences in species abundance may be attributable to differences in annual rainfall totals and water duration in ponded areas (Harding Lawson Associates 2001). The total combined population estimates for the two areas where monitoring occurred in 1998, 1999, and 2000 were 500-1500, 56,000, and 162,500 individuals, respectively. The areas on the former military base that contain Contra Costa goldfields are being transferred to the BLM as a habitat reserve Natural Resource Management Area. Contra Costa goldfields in Monterey County are located 60 miles south of other locations where the species has been documented. This unit is essential to the conservation of Contra Costa Goldfields because it contains the southern-most extant occurrence of the species.

Hoover's Spurge Criteria

In proposing critical habitat units for Hoover's Spurge we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of these species.

The CNDDB (2001) includes 30 occurrences of Hoover's spurge, six of which were discovered in 1992 (three each in Glenn and Tulare counties). Of the 30 occurrences, one each in Tehama and Tulare counties are classified as extirpated; two others, in Butte and Tehama counties, are “possibly extirpated” because this species was not observed for 2 consecutive years (Stone et al. 1988, CNDDB 2001). Of the 26 occurrences presumed to be extant, only 12 have been observed within the past decade (CNDDB 2001).

The main area of concentration for Hoover's spurge is within the Vina Plains area of Tehama and Butte counties, which contains over half of the 26 presumed extant occurrences for Hoover's spurge (CNDDB 2001). One other site in the same region is near Chico in Butte County. Other extant occurrences of the species are found in the Visalia-Yettem area of Tulare County, the Hickman-La Grange area of Stanislaus County, the Sacramento National Wildlife Refuge in Glenn County, and on the Bert Crane Ranch in Merced County (CNDDB 2001).

One population of Hoover's spurge in Tulare County and another in Tehama County were destroyed when the areas were converted for agricultural use (CNDDB 2002). Agricultural conversion continues to threaten Hoover's spurge, particularly in Stanislaus County (Stone et al. 1988). However, more subtle factors such as changes in hydrology, invasion by aggressive plants, and inappropriate livestock grazing regimes constitute a greater threat to survival of the species at this time. Five of the remaining occurrences of Hoover's spurge are subject to obvious hydrologic threats; four of the five are in the San Joaquin Valley and the fifth is in the Vina Plains. Hydrology has been altered by (1) construction of levees and other water barriers and (2) by runoff from adjacent agricultural operations, roads, and culverts. Due to these changes, some pools receive insufficient water and others remain flooded for too long to allow growth of Hoover's spurge. Although no occurrences have been completely extirpated due to hydrologic changes, the species has been eliminated from one or more individual pools at several sites and a number of the remaining populations appear to be declining (Stone et al. 1988, Stebbins et al. 1995, CNDDB 2002).

Competition from invasive native or non-native plant species threatens nine of the extant occurrences, including eight in the Vina Plains and one on the Sacramento National Wildlife Refuge in Glenn County. Native competitors of Hoover's spurge include coyote-thistle, alkali mallow (Malvella leprosa, a noxious weed according to Hill 1993), lippia (Phyla nodiflora), hard-stemmed tule (Scirpus acutus var. occidentalis), alkali bulrush (Scirpus maritimus), and cocklebur. Non-native competitors include bindweed (a noxious weed according to Dempster 1993) and swamp grass (Crypsis schoenoides) (Silveira in litt. 2000, CNDDB 2001). On the Vina Plains Preserve, the pools with Hoover's spurge also had the highest frequency of bindweed, at least in 1995 (Alexander and Schlising 1997). Increasing dominance by these competitors may be associated with changes in hydrology and livestock grazing practices (Stone et al. 1988, Alexander and Schlising 1997, CNDDB 2002).

The issue of livestock grazing effects on Hoover's spurge is complex. In general, moderate levels of grazing appear to be compatible with Hoover's spurge and presumably benefit the species by reducing competition from other plants (Stone et al. 1988). Livestock do not eat Hoover's spurge because it grows so close to the ground and possibly because the milky sap is toxic (Wheeler 1941, Stone et al. 1988). During 1986 and 1987, Stone et al. (1988) deemed the intensity of cattle grazing at most Hoover's spurge sites to be appropriate. In fact, several species experts (Stone et al. 1988, Silveira in litt. 2000) have cautioned that decreases in grazing intensity could be detrimental to Hoover's spurge. On the other hand, cattle trampling has seriously reduced Hoover's spurge populations at one site each in Butte and Stanislaus counties (Stone et al. 1988), and increased summer stocking rates at other sites could similarly damage those populations.

Populations with small numbers of plants may be more vulnerable to extirpation from random events (Shaffer 1981, Menges 1991). This may be the case for at least four of the known occurrences, which total fewer than 100 individuals even in favorable years (CNDDB 2002).

Hoover's Spurge Unit Review

We conducted a review across the range of Hoover's spurge to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the documented presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Vina Plains Unit, Tehama and Butte Counties (11,673 ha (28,845 ac))

This unit is proposed as critical for Hoover's spurge because it supports numerous occurrences of the species within vernal pools on acidic soils over iron-silica cemented hardpan, including Anita and Tuscan soils (USDA 2001, Holland 1998, CNDDB 2002). The Vina Plains Unit contains over 50 percent of the known occurrences of Hoover's spurge, including several large, stable occurrences (CNDDB 2002). This area represents the northern extent of the species range.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination and reproduction.

The majority of the lands included within this unit are privately owned. This unit contains TNC's 1862 ha (4,600 ac) Vina Plains preserve. The preserve contains over 300 species of plants and diverse communities of aquatic invertebrates. Since the 1960s, the Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating of the effects of grazing and fire on vernal pool plants (Griggs 2000). Much of the basic life history information known about Hoover's spurge was collected at Vina Plains (e.g., Stone et al. 1988, Alexander and Schlising 1997). The results of this research have provided crucial information to guide management and monitoring of vernal pool ecosystems and to identify factors which influence population dynamics of a number of endangered species.

The Vina Plains is open to the public and provides excellent outreach and educational opportunities. In addition to TNC, the importance of vernal pool habitats in this area has been recognized by the CDFG, the Service, the EPA, the CNPS, the NRCS's WRP, and by researchers at the CSU at Chico, who have all supported research and conservation efforts for Hoover's spurge and other vernal pool species within this unit. Urban development north of Chico and the conversion of grazed lands to more intensive agricultural uses threaten vernal pool habitat within this unit.

This unit for Hoover's spurge occupies the area south of Toomes Creek and north of Pine Creek to near Cana Highway. State Route 99 bisects this unit and the western boundary generally parallels the Southern Pacific Railway line. This unit overlaps Unit 7 for vernal pool fairy shrimp, Unit 3 for vernal pool tadpole shrimp, Unit 1 for Conservancy fairy shrimp, Unit 2 for Greene's tuctoria, Unit 1 for Hoover's spurge, and Unit 4 for slender Orcutt grass. Additional sensitive vernal pool species occurring in this unit include California linderiella and Bogg's Lake hedge-hyssop. Property ownership and protection within this unit includes CDFG (0.4 ha (1 ac)), CDFG administration (0.4 ha (1 ac)), TNC (2,295 ha (5,738 ac)), TNC easements (4,661 ha (11,653)), and WRP easements and agreements (57 ha, 142 ac)).

Unit 2, Butte Unit, Butte County (979 ha (2,418 ac))

This unit is proposed as critical habitat for Hoover's spurge because it supports the species within vernal pools on acidic Tuscan soils over iron-silica cemented hardpan (CNDDB 2002, Liss 2001, USDA 2001, Holland 1998, EPA 1994) and the vernal pool habitat remains inundated for sufficient periods of time to allow Hoover's spurge to complete its life-cycle. This unit represents one of only three areas where Hoover's spurge is known to occur in the Sacramento Valley, and is over 225 km (140 mi) from the nearest occupied areas to the south.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination and reproduction. Hoover's spurge is known from only seven general locations across its entire range, and each of these locations is essential to the conservation of this species.

This unit for Hoover's spurge occupies the area north of the intersection of State Route 99 and Route 149 in Butte County. The eastern boundary extends up the watershed of Clear Creek and the western boundary extends south paralleling State Route 99 to Little Dry Creek. This unit is within Unit 9 for vernal pool fairy shrimp and Unit 4 for vernal pool tadpole shrimp, and coincides with Unit 3 for Greene's tuctoria and Units 2 and 3 for hairy Orcutt grass. All the land within this unit is privately owned.

Unit 3, Sacramento National Wildlife Refuge Unit, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical habitat for Hoover's spurge because it contains multiple occurrences of the species within alkaline vernal pools on Willows and Riz soil types (Holland 1998, Silveira 2000, CNDDB 2002). The vernal pool habitat remains inundated for sufficient periods of time to allow Hoover's spurge to complete its life cycle. This habitat contributes to the diversity of environmental conditions in which Hoover's spurge is known to occur. This area represents one of only three general locations where Hoover's spurge is found in the Sacramento Valley, and is one of only seven areas across its entire range where Hoover's spurge is known to occur. This unit is over 40 km (25 mi) from the nearest unit to the northeast, and over 225 km (140 mi) from the nearest unit to the south. Hoover's spurge occurrences at the Sacramento National Wildlife Refuge have been monitored annually since 1992 (Silveira in litt. 2000).

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination and reproduction to take place.

This unit for Hoover's spurge occupies the vernal pool habitat and surrounding area east of Interstate 5 to the Colusa Trough from Riz Road on the north and Delevan Road on the south. The area encompasses a portion of the Sacramento National Wildlife Refuge (5,126 ha (12,816 ac)). The remaining portions of the unit are privately owned. This unit is also part of vernal pool fairy shrimp Unit 10, and vernal pool tadpole shrimp Unit 5, and coincides with Unit 2 for Conservancy fairy shrimp, Unit 1 for Greene's tuctoria, and Unit 3 for hairy Orcutt grass. Other vernal pool and associated upland species found in the unit include pappose spikeweed, Fremont's goldfields, alkali goldfields, Scribe's popcorn flower, Hoover's downingia, folded downingia, Heckard's peppergrass, heartscale, brittlescale, San Joaquin spearscale, Ferris' milk-vetch, spike-primrose, sessile mousetail, and palmate-bracted bird's beak.

Unit 4, Waterford Unit, Stanislaus and Tuolumne Counties (16,839 ha (41,609 ac))

This unit is proposed as critical habitat for Hoover's spurge because it supports the species within vernal pools on Whitney sandy loam soils that maintain the necessary timing and duration of inundation for Hoover's spurge germination, growth, and reproduction (USDA 2001, CNDDB 2002). This unit contains soils that are typically older than those of the alluvial terraces in the Sacramento area which are estimated to be early Pleistocene.

The Waterford Unit contains very high quality, hydrologically intact vernal pool complexes important for the conservation of Hoover's spurge. Hoover's spurge is sparsely distributed in the southern Sierra Nevada foothills, and these occurrences are highly disjunct from the occurrences of Hoover's spurge in the northern portion of the species range. This unit is over 225 km (140 mi) from the nearest units to the north. The largest threat to Hoover's spurge in this unit is agricultural conversion (Stone et al. 1988). Cattle trampling has also impacted an occurrence of Hoover's spurge in the southeastern region of the unit (CDNNB 2001). There are numerous deep pools in this area that provide suitable habitat for Hoover's spurge because the duration of inundation is generally longer than in shallow pools. These pools contain habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal of the species.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. The Waterford Unit is bordered by the Tuolumne River to the south. The Modesto Reservoir is adjacent to the southwest boundary of the unit. Warnerville Road cuts through the northern portion of the unit. The City of La Grange is located southeast of the unit. The eastern boundary extends into the low elevation foothills of the Sierra Nevada. Vernal pools in the Waterford Unit are located mainly in eastern Stanislaus County, but overlap into western Tuolumne County. This unit coincides with Colusa grass Unit 4, San Joaquin Valley Orcutt grass Unit 1, and hairy Orcutt grass Unit 4. It overlaps succulent owl's-clover Unit 2 and Greene's tuctoria Unit 6. Other sensitive vernal pool species found within this unit include California tiger salamander, western spadefoot toad, dwarf downingia, and California linderiella. CDFG administers approximately 0.8 ha (2 ac) of this unit. The remaining land within this unit is privately owned.

Unit 5, Turlock Unit, Stanislaus and Merced Counties (19,850 ha (49,049 ac))

This unit is proposed as critical habitat for Hoover's spurge because it contains occurrences of the species within large vernal pools on Meikle soils, including two of the seven known occurrences of Hoover's spurge on the eastern margin of the San Joaquin Valley (Holland 1998, CNDDB 2002). One occurrence is within the well-known Hickman pools in Stanislaus County. Not only does the Hickman pool complex contain one of the largest vernal lakes in California at more than 121 ha (300 ac), but it also exhibits tremendous biodiversity (Medeiros 2002).

The Turlock Unit contains large intact and contiguous vernal pool grassland areas that help maintain connectivity between hairy Orcutt grass habitat to the north and south. There are numerous vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths in this unit to sustain Hoover's spurge germination, growth and reproduction. Hoover's spurge populations in Stanislaus County typically flower from mid-June into October, whereas those in Merced and Tulare counties typically flower from late May through July (Alexander and Schlising 1997). The Hoover's spurge habitat in this unit is important to conserve phenotypic variation within the species and to maintain the geographic distribution of Hoover's spurge throughout its range.

The largest threat to this species in this unit is agricultural conversion (Stone et al. 1988). The watershed containing the vernal pools has been breached by hundreds of acres of orchards that have been planted upstream. East of the Hickman vernal pools, there is a large, hydrologically intact vernal pool complex that likely contains other occurrences of Hoover's spurge.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. The Turlock Unit is bordered by the Tuolumne River to the north and the Merced River to the south. The unit lies between the towns of La Grange and Snelling. County Road J9 runs west of the unit and the eastern edge is located in the low elevation foothills of the Sierra Nevada. Vernal pools in the Turlock Unit are located in Stanislaus and Merced counties. This unit coincides with Colusa grass Unit 6, hairy Orcutt grass Unit 5, succulent owl's-clover Unit 3A, and vernal pool fairy shrimp Unit 21. Other sensitive vernal pool species found within this unit include California tiger salamander, Hartweg's golden sunburst, and dwarf downingia. California State Parks owns approximately 24 ha (60 ac) within this unit. The remaining land within this unit is privately owned.

Unit 6, Grasslands Unit, Madera, Merced and Stanislaus Counties (14,310 ha (35,359 ac))

This unit is proposed as critical habitat for Hoover's spurge because it support occurrences of the species within saline-alkaline vernal pools on Lewis soils (USDA 2001, CNDDB 2002). The unit boundary was designated to include occurrences of Hoover's spurge and the vernal pool complex in which they occur (Holland 1998). The vernal pools, swales, and associated uplands within this unit contribute to the filling and drying of Hoover's spurge habitat, and maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination, growth and reproduction, and dispersal.

The Grasslands Unit includes portions of the Kesterson, San Luis, and Merced National Wildlife Refuges (3,232 ha (7,985 ac). The remaining land within this unit is privately owned. This unit contains a diversity of vernal pool types, including vernal pools occurring on Delhi-Dello-Himar, Solano-Caypay-Willows, Rossi-Waukena, and Lewis-Landlow soils (USDA 1994). This unit contains the majority of the remaining vernal pool habitats in the San Joaquin Valley (Holland 1998). Threats to remaining vernal pool habitats within this unit include agricultural conversion.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit represents Unit 23 for vernal pool fairy shrimp, Unit 7 for Conservancy fairy shrimp, and Unit 16 for vernal pool tadpole shrimp. The western half of this unit represents Unit 8 for Colusa grass. In addition to the species mentioned above, vernal pool smallscale, alkali milk-vetch, western spadefoot toad, and California linderiella are present in this unit as well.

Unit 7 A, B, C, and D, Tulare Unit, Tulare County (12,375 ha (30,578 ac))

This unit is proposed as critical habitat for Hoover's spurge because it supports almost 20 percent of the known occurrences of the species, including occurrences found within vernal pools on Lewis soils (USDA 2001, CNDDB 2002). This unit comprises the southern extent of the range of Hoover's spurge. Occurrences within this unit are more than 110 km (68 mi) distant from the nearest Hoover's spurge unit to the north. Peripheral populations may have genetic characteristics essential to overall long-term conservation of the species (i.e., they may be genetically different than more central populations) (Lesica and Allendorf 1995). Hoover's spurge populations in Tulare County typically flower from late May through July, whereas those in Stanislaus and Sacramento County typically flower from mid-June into October (Alexander and Schlising 1997). This phenotypic variation also suggests there may be regional differences between these and other occurrences in other portions of the species range.

This unit includes several protected areas, including the Sequoia Fields Ecological Reserve and the Stone Corral Ecological Reserve in Tulare County managed by CDFG (355 ha (877 ac)) as well as 13 ha (33 ac) of BLM land. Other areas within this unit are privately owned, and are threatened by conversion to irrigated agriculture of range. This unit contains scattered vernal pool complexes in northwestern Tulare County. This unit contains deeper pools that maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool plant germination, growth and reproduction, and dispersal.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. There are four subunits within the Tulare Unit. The westernmost subunit is located east of J19. Road 63 cuts through its eastern edge. St. Johns River is south of the subunit and the Southern Pacific Railroad runs northeast of the unit. The other three subunits are located east of Road 63. The smallest subunit lies directly east of the westernmost subunit. Road 201 passes through both of the easternmost subunits. The subunit that lies next to the easternmost subunit contains vernal pool habitat north of Stokes Mountain. In the south it is bordered by Cottonwood Creek. The easternmost subunit extends into the low elevation foothills of the Sierra Nevada. Colvin Mountain is located within its southwest boundary. Road 245 bisects this subunit and the south side of Red Mountain is within its northeast boundary. Tulare Unit coincides with San Joaquin Valley Orcutt grass Unit 7, and overlaps with vernal pool tadpole shrimp Unit 18 and vernal pool fairy shrimp Unit 26. Other sensitive vernal pool species found within this unit include the California tiger salamander, spiny-sepaled button-celery, and western spadefoot toad.

Succulent Owl's-clover

In proposing critical habitat units for succulent owl's-clover we evaluated the life history and current distribution of the species, the primary constituent elements, and the threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of this species and to delineate units so that threats to this species might be minimized.

Succulent owl's-clover is currently known from 63 occurrences, of which one in Fresno County is considered to be “possibly extirpated” (CNDDB 2002) because the site had been disced when it was last visited in 1981. Another site in Fresno County also may be extirpated. Among the areas where succulent owl's-clover is known to occur, more than half are in Merced County. Additional occurrences are found in Fresno, Madera, Stanislaus, and San Joaquin counties (CNDDB 2001).

The current status of most succulent owl's-clover populations is unknown because most sites have not been visited for decades. Inappropriate cattle grazing and trampling degraded three occurrences of succulent owl's-clover. One of the same sites plus three others were degraded by discing. The CNDDB (2002) lists one of the latter as “possibly extirpated” due to discing. However, succulent owl's-clover persisted at another site that had been disced, although the population size was reduced by an order of magnitude (CNDDB 2001).

A wide variety of factors threaten the continued existence of succulent owl's-clover, including urban development, year-round or summer livestock grazing, changes in hydrology, agricultural conversion, gravel mining, and small population size. Construction of the proposed new UC campus in Merced County, plus the associated residential community and access roads, threatens the extensive population in that area. Different types of urban development that threaten numerous known occurrences include planned housing subdivisions in Fresno, Madera, and San Joaquin counties; a freeway expansion in Madera County; and a proposed landfill in Fresno County (Service 1997, Stebbins in litt. 2000, CNDDB 2001).

Approximately two-thirds of the reported occurrences, including those at the UC Merced site, were subject to cattle grazing when they were discovered (EIP Associates 1999, CNDDB 2001). However, grazing is not necessarily detrimental to succulent owl's-clover. Winter and spring grazing may be helping in controlling non-native grass invasions (Barry 1998). Stebbins et al. (1995) noted that among the sites they studied, those that were grazed “did not appear to suffer long-term damage due to grazing.” Damage from livestock would be harmful when pools are dry and during the time that the water is evaporating; thus summer or year-round grazing poses a threat (Barry 1998).

Hydrological alterations can create conditions unsuitable for succulent owl's-clover and other vernal pool plants by increasing or decreasing the depth and duration of inundation. Threats due to alterations in natural hydrology include the Merced County Stream Channel Project proposed by the U.S. Army Corps of Engineers (Corps)(Service 1997a) and proposed enlargement of Burns Reservoir in Merced County (CNDDB 2001), which collectively threaten seven occurrences of succulent owl's-clover. Expansion of agricultural operations threatens three occurrences in Fresno and Madera counties that are surrounded by orchards, vineyards, or citrus groves (CNDDB 2001). Also, populations in grain fields already have been subject to discing, as mentioned above. A proposed gravel mine threatens one occurrence in Fresno County (Service 1997a).

Threats posed by small population size are less immediate but also potentially significant. Random genetic, environmental, or other processes can lead to the extirpation of small populations; adequate populations would be in the range of thousands to millions (Shaffer 1981, Thomas 1990, Menges 1991). Species that are subject to extreme fluctuations in population size from year to year are particularly vulnerable to chance events (Thomas 1990). Among the 24 populations of succulent owl's-clover for which size estimates were given, 10 consisted of fewer than 100 plants at their peak size (CNDDB 2001, Stebbins in litt. 2000).

Succulent Owl's-Clover Unit Review

We conducted a regional review across the range of succulent owl's-clover to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the presence of the species and the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Southeast Sacramento Valley Unit, Sacramento and San Joaquin Counties (1,052 ha (2,598 ac))

This unit is proposed as critical habitat for succulent owl's-clover because it contains occurrences of the species living within vernal pools occurring on San Joaquin soils that provide the necessary timing and length of inundation for succulent owl's-clover germination, growth, and reproduction (Holland 1998, Sacramento County 1999, CNDDB 2002).

The site is a “Nature Study Area” for the UC Cooperative Extension (CNDDB 2001). This unit represents the northern most extent of succulent owl's-clover range and is the only unit designated for this species within the Sacramento Valley. The unit is isolated from other succulent owl's-clover occurrences to the south in the San Joaquin Valley by a distance of over 80 km (50 mi). Isolated and peripheral populations such as this may have genetic characteristics essential to the overall long-term conservation of the species (i.e., they may be different from more central populations) (Lesica and Allendorf 1995).

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for succulent owl's-clover germination and reproduction.

This unit for succulent owl's-clover occupies the area east of Galt near Dustin and Liberty roads. All the lands included within this unit are privately owned. Urban expansion and conversion from grazing to other agricultural practices, particularly vineyards have greatly affected existing vernal pool habitats throughout this area. Other sensitive vernal pool species found within this unit includes the California tiger salamander.

Unit 2, Waterford Unit, Stanislaus and Tuolumne Counties (14,131 ha (34,917 ac))

This unit is proposed as critical habitat for succulent owl's-clover because it supports occurrences of the species within hardpan vernal pools on alluvial terraces on Amador and Redding soils that provide the necessary timing and length of inundation essential to the conservation of the species (CNDDB 2002). This is the northernmost extent of succulent owl's-clover's range within the San Joaquin Valley, and is over 80 km (50 mi) from the isolated occurrence to the north. This unit contains a variety of pools and ephemeral habitats in which the plants are known to occur, including shallow and deep pools and pools with both long and short inundation periods. These pools contain appropriate conditions for germination, growth, reproduction, and dispersal of succulent owl's-clover. The Waterford Unit is important for the survival of succulent owl's-clover because it represents large areas of contiguous habitat with relatively intact hydrology. All the lands within this unit are privately owned.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. The Waterford Unit is bordered by the Tuolumne River to the south. The Modesto Reservoir is adjacent to the southwest boundary of the unit. Warnerville Road cuts through the northern portion of the unit. The City of La Grange is located southeast of the unit. The eastern boundary extends into the low elevation foothills of the Sierra Nevada. Vernal pools in the Waterford Unit are located mainly in eastern Stanislaus County, but overlap into western Tuolumne County. This unit overlaps with San Joaquin Valley Orcutt grass Unit 1, hairy Orcutt grass Unit 4, Colusa grass Unit 4, Hoover's spurge Unit 4, and Greene's tuctoria Unit 6. Other sensitive vernal pool species found within this unit include California tiger salamander, western spadefoot toad, dwarf downingia, and California linderiella.

Unit 3A and B, Merced Unit, Merced County (63,352 ha (156,542 ac))

This unit is proposed as critical habitat for succulent owl's-clover because it supports over 50 percent of the known occurrences of the species, living within vernal pools on Redding, Corning, and Pentz soil series that provide the primary constituent elements essential to the conservation of the species (CNDDB 2002). This unit represents the largest remaining habitat area for succulent owl's-clover, and includes the largest block of pristine, high density vernal pool grasslands remaining in California (Holland 1998, Vollmar 1999). This unit is important to maintain a diversity of habitats for succulent owl's-clover, and supports hydrologically intact vernal pool complexes that are likely to maintain ecosystem processes important to the recovery of succulent owl's-clover.

A majority of the land in this unit is privately owned, and is used to graze cattle. The integrity of the vernal pool complexes in eastern Merced is threatened by the proposed UC Merced Campus and associated development. Succulent owl's-clover has been found in 296 vernal pools in the proposed campus and community area, although only 34 percent of the area was surveyed intensively (EIP Associates 1999). Construction of facilities to educate and serve twenty-five thousand UC students as well as faculty, staff, and their families within the vernal pool complexes in eastern Merced County, could have a major impact on the survival and recovery of succulent owl's-clover. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Indirect and cumulative impacts of the proposed 1,673 ha (4,133 ac) campus and associated community may be minimized with the creation of a 2,036 ha (5,030 ac) preserve intended to protect sensitive vernal pool habitat, to be purchased with money donated by the Packard Foundation.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. The Merced Unit is comprised of two subunits, Subunit A is located north of the Merced River, and south of Dry Creek. Subunit B is located south of the Merced River and north of Mariposa Creek Both subunits are located east of State Highway 99. Approximately 419 ha (1,048 ac) is owned by the DOD, 3 ha (8 ac) by U.S. Bureau of Reclamation (BOR), 10 ha (26 ac) by California State Parks. TNC has 4,513 ha (11,283 ac) of easement lands within this unit. The remaining lands within this unit are privately owned. The Merced Unit overlaps with vernal pool tadpole shrimp Unit 15, vernal pool fairy shrimp Unit 22, Conservancy fairy shrimp Unit 6, hairy Orcutt grass Unit 5, Hoover's spurge Unit 5, Greene's tuctoria Unit 7, San Joaquin Valley Orcutt grass Units 2 and 3, and Colusa grass Units 5 and 6. Other sensitive vernal pool species found within this unit include California linderiella, California tiger salamander, shining navarretia, dwarf downingia, and Bogg's Lake hedge-hyssop.

Unit 4, Madera Unit, Madera County (33,071 ha (81,717 ac))

This unit is proposed as critical habitat for succulent owl's-clover because it supports multiple occurrences of the species within hardpan vernal pools on soils of alluvial fans and terraces, including San Joaquin soils (CNDDB 2002). This unit is important for the survival of succulent owl's-clover because it represents large areas of contiguous habitat with relatively intact hydrology. These pools are typically found in vernal pool/swale complexes on mima mound topography. This unit contains vernal pools and other ephemeral features and associated watersheds that maintain suitable periods of pool inundation, water quality, and soil moisture for succulent owl's-clover germination, growth, reproduction, and dispersal.

Most of the area within this unit is on private land, although a large population of succulent owl's-clover occurs on property acquired by the California Department of Transportation for mitigation purposes (CNDDB 2001). The integrity of vernal pool complexes and their associated watersheds in the Madera Unit is threatened by agricultural conversion and urban encroachment.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. Located entirely in Madera County, this unit contains vernal pool habitat extending from the Chowchilla River in the north to the San Joaquin River in the south. All vernal pools in this unit are located east of State Highway 99. Land ownership within the unit includes 3 ha (8 ac) by BOR, 2 ha (5 ac) by NPS, 47 ha (117 ac) by CDFG, and 9 ha (22 ac) by State Land Commission. The Madera Unit overlaps hairy Orcutt grass Units 6 and 7, Greene's tuctoria Unit 8, San Joaquin Valley Orcutt grass Units 4 and 5 and vernal pool fairy shrimp Unit 24A. Other sensitive vernal pool species found within this unit include spiny-sepaled button-celery, California tiger salamander, western spadefoot toad and California linderiella.

Unit 5, Fresno Unit, Fresno County (11,888 ha (29,375 ac))

This unit is proposed as critical habitat for succulent owl's-clover because it contains occurrences of the species growing within vernal pools formed on Fallbrook, Ramona, San Joaquin, Vista, and Pollasky soil series (CNDDB 2002). The diversity of vernal pool types found within the Fresno Unit contributes to the range of ecological conditions in which succulent owl's-clover occurs. This area represents the southern extent of the species range. This unit contains suitable habitat within annual grassland communities to enable the species to carry out its life-cycle. Some habitat in this unit consists of typical “bowl-like” pools, whereas other areas are more similar to swales. Vernal pools within this unit have been destroyed by conversion to irrigated agriculture, as well as urban encroachment from the cities of Fresno and Clovis.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Located in Fresno County, this unit contains vernal pool habitat extending from the San Joaquin River in the north to Shaw Avenue in the south. The western boundary of this unit lies east of Fresno and Clovis and the eastern boundary parallels the low elevation foothill region of the Sierra Nevada. Property ownership and protection within this unit includes CDFG (0.4 ha (1 ac)) and CDFG administered land (0.4 ha (1 ac)). The remainder of the property within this unit is privately owned. The Fresno Unit overlaps San Joaquin Valley Orcutt grass Unit 5 and vernal pool fairy shrimp Unit 24B. Other sensitive vernal pool species found within this unit include California linderiella, California tiger salamander, and western spadefoot toad.

Unit 6A and B, Table Mountain Unit, Fresno and Madera Counties, (1,723 ha (4,258 ac))

This area is proposed as critical habitat for succulent owl's-clover because it supports occurrences of the species within Northern Basalt Flow vernal pools (CNDDB 2002). This is the only area where succulent owl's-clover is found on this vernal pool type. Northern Basalt Flow pool complexes, such as Table Mountain, are extremely rare, occurring only on ancient terraces and hilltops. Basalt tables are perched on narrow, sinuous basalt mesas above the surrounding low-lying terrain. They typically contain small, irregularly clustered pools with “flashy hydrology” (Keeler-Wolf et al. 1998). They are less common than hardpan and claypan pools that are typically found in this region, and occur in complexes that are less dense than habitat in units further north.

Three occurrences of succulent owl's-clover within this unit are wholly or in part within designated reserves, which are on two “tabletop” mountains near Millerton Lake. The Sierra Foothill Conservancy's Big Table Mountain Preserve includes one of these occurrences and a portion of another, which is shared with the BLM. The other is in the CDFG's Big Table Mountain Ecological Reserve. A fourth occurrence, which is on a nearby tabletop, is partially under the control of the BLM and partly in private ownership. A cooperative group consisting of the CDFG, California Department of Parks and Recreation, Sierra Foothill Conservancy, BLM and BOR has developed a management and monitoring plan for Big Table Mountain. Initial efforts of the plan will focus on grazing as a means to control non-native grasses while comparing population trends of threatened and endangered species in grazed and ungrazed portions of the tableland (Griggs in litt. 2000a). BLM owns approximately 149 ha (371 ac) and CDFG owns approximately 429 ha (172 ac) of land within this unit. TNC has 256 ha (650 ac) of conservation easements within this unit. The BLM has attempted to protect the occurrence on the other tabletop mountain by erecting fencing to prevent trespass by cattle (Franklin in litt. 1993).

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. Unit 6 for succulent owl's-clover is comprised of two subunits. Both subunits are located east of Millerton Lake on basalt mesas above the San Joaquin River. Subunit 6B is located on Kennedy Table in Madera County, and Subunit 6A is directly south of this unit across the San Joaquin River on Table Mountain in Fresno County. The Table Mountain Rancheria is south of this unit. Unit 6 coincides with vernal pool fairy shrimp Unit 25, vernal pool tadpole shrimp Unit 17, and San Joaquin Valley Orcutt grass units 6A and 6B. Other sensitive vernal pool species found within this unit include Bogg's lake hedge-hyssop and California linderiella.

Colusa Grass Criteria

In proposing critical habitat units for Colusa grass, we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are most likely to contribute to the conservation of Colusa grass.

Currently, the CNDDB (2001) includes 59 occurrences of Colusa grass; 48 occurrences are presumed to be extant and 11 others are either known or presumed to be extirpated. The extant populations occur primarily in the foothills region of the San Joaquin Valley, where 80 percent known occurrences are found northeast of the city of Merced in Merced County and east of Hickman in Stanislaus County. Of the remaining extant occurrences, four are in central Merced County, and two each occur in southeastern Yolo and central Solano counties (Stone et al. 1988, Keeler-Wolf et al. 1998, CNDDB 2001). This species has been extirpated from Colusa County (CNDDB 2001).

Colusa grass declined primarily because pools in which it occurred were destroyed by conversion to irrigated agriculture, primarily to orchards and vineyards (Crampton 1976, Medeiros 1976, CNDDB 2002). Agricultural conversion continues to threaten Colusa grass. In eastern Stanislaus County agricultural conversion threatens the 16 occurrences (33 percent) there. Dry-land farming there is gradually being replaced by irrigated agriculture; the former apparently is compatible with the persistence of Colusa grass, but the latter is not (Crampton 1959, Crampton 1976).

Other factors that extirpated populations of Colusa grass included surface disturbances and degradation of vernal pool hydrology. At least 9, and possibly 11, occurrences have been extirpated as a result of these factors, although several others most likely were eliminated before being reported (Stone et al. 1988). Changes in natural hydrology, such as draining pools or creating reservoirs, could create unsuitable conditions for Colusa grass by decreasing or increasing inundation periods. The two Yolo County occurrences are threatened by herbicide run-off from adjacent agricultural operations (CNDDB 2002).

Additional factors threaten the survival of Colusa grass, particularly the problem of small population size. Although populations may drop to only a few visible plants in certain years, seven populations consisted of fewer than 100 plants even at their peak (CNDDB 2002) and thus are likely to be small populations. Non-native plants and invasive native species could invade Colusa grass occurrences and may be particular problems in combination with other factors such as decreased inundation and inappropriate livestock grazing (Stone et al. 1988, Witham in litt. 2000a). Grasshopper foraging has been observed on Colusa grass (Stone et al. 1988), but the extent of this threat is unknown.

Colusa Grass Unit Review

We conducted a regional review across the range of Colusa grass to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Davis Communications Annex and Grasslands Area Unit, Yolo County (192 ha (474 ac))

This unit is proposed as critical for Colusa grass because it contains one of six areas where the species is known to occur (CNDDB 2002, Yolo County Parks 2001, EIP Associates 2001) within large vernal playa pools of the Pescadero soil series (Holland 1998, USDA 2001, Yolo County 1995).

The unit boundary was drawn to include the vernal pool complex mapped by Holland (1998) and Yolo County Parks (2001) where Colusa grass is known to occur. This vernal pool complex maintains suitable periods of pool inundation, water quality, and soil moisture for Colusa grass germination, growth and reproduction, and dispersal, but not necessarily every year. Colusa grass in this unit is threatened by altered hydrology, contamination, competition with invasive plant species, and surface disturbances such as discing.

This unit is located southeast of the City of Davis and south of the South Fork of Putah Creek. This unit's western boundary coincides with the Solano and Yolo county line. This unit also represents Unit 1 for Solano grass, and is a portion of Unit 10 for vernal pool tadpole shrimp. The unit contains land owned by Yolo County. Approximately 128 ha (322 ac) is owned by the DOD.

Unit 2, Jepson Prairie Unit, Solano County (7,153 ha (17,675 ac))

This unit is proposed as critical for Colusa grass because it supports the species (CNDDB 2002) within large, alkaline, playa type vernal pools (Holland 1998, USDA 2001, Solano County 2000, Solano County Farmlands and Open Space 2000). These pools occur on Pescadero and Antioch-San Ysidro soil series, and contribute to the diversity of vernal pool types where the species is found. The unit boundary was drawn to include the vernal pool complex where Colusa grass is known to occur. The pools, swales, and adjacent uplands that comprise this complex are essential to maintain the necessary timing and length of pool inundation for Colusa grass germination, growth, pollination, seed production, and dispersal. This unit includes one of the largest contiguous areas of habitat remaining for the species. The relatively undisturbed, hydrologically intact condition of the vernal pool habitats within this unit increase the likelihood that it will continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for Colusa grass.

This unit includes the Jepson Prairie Preserve (623 ha (1,558 ac), jointly managed by the Solano County Farmlands and Open Space and the UC Reserve System. Jepson Prairie contains large playa-like vernal pools which may be over several acres in size, including the 32 ha (80 ac) Olcott Lake. These larger pools often occur in complexes with smaller pools and hogwallow depressions. Jepson Prairie has long been recognized as an outstanding example of vernal pool ecosystems. In 1987, the NPS named Jepson Prairie a National Natural Landmark, a designation given to well preserved sites that illustrate a particular type of natural feature and provide high quality habitat for threatened or endangered species. Jepson Prairie is the target of ongoing conservation planning and active management. As part of the UC Reserve System, this area also provides critical research opportunities for scientists to study vernal pool species, including Colusa grass. The unit also contains lands totaling 248 ha (620 ac) owned and approximately 64 ha (161 ac) administered by CDFG. Additional lands are owned by DOD (93 ha (233 ac)), and the State Land Commission (7 ha (17 ac)), with another 436 ha (1,090 ac) of private land protected under WRP easements or agreements. Within the greater Jepson Prairie grassland area, existing vernal pools are threatened by agricultural conversion, landfill expansion, power plant construction, and utility maintenance.

This unit is situated east of the City of Fairfield, south of the City of Dixon, and north of the Montezuma Hills and the confluence of the Sacramento and San Joaquin rivers. This unit is also described as Unit 2 for Solano grass. This unit is encompassed by Unit 3 for Conservancy fairy shrimp, Unit 11 for vernal pool tadpole shrimp, and Unit 16 for vernal pool fairy shrimp. This unit also supports a diverse community of plants and animals, including the only known occurrence of delta green ground beetle, and occurrences of California tiger salamander, alkali milk-vetch, Bogg's Lake hedge-hyssop, legenere, California linderiella, and midvalley fairy shrimp.

Unit 3, Farmington Unit, Stanislaus County (16,475 ha (40,709 ac)

This unit was identified as critical for Colusa grass because the species is found (CNDDB 2002) within vernal pools on high terrace landforms and Redding-Pentz-Peters soil complexes (USDA 2001). The impermeable layers underlying these occupied vernal pools are generally iron-silica cemented hardpan. The Farmington Unit contains pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Colusa grass germination, growth, and reproduction. Habitat in this unit includes deeper pools that are most likely to provide the long inundation period required for germination of Colusa grass (EIP Associates 1999). This unit is isolated from the other Colusa grass units to the north by over 80 km (50 mi).

The Farmington unit is located in northeast Stanislaus County. It is hydrologically separated from units to the south by the Stanislaus River. The eastern boundary generally parallels the Calaveras County Line. Woodward Reservoir and the town of Oakdale are all located outside and to the west of the unit. The unit is generally south of State Highway 4 and north of State Highway 108. The unit boundary was drawn to include these species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Lands within this unit are privately owned.

Unit 4, Waterford Unit, Stanislaus and Tuolumne Counties (35,134 ha (86,814 ac))

The Waterford Unit was identified as critical habitat for Colusa grass because it contains large occurrences of Colusa grass. Approximately one-fifth of all extant occurrences are found within this unit (CNDDB 2002). These occurrences are found within vernal pools formed on alluvial terraces and associated Whitney soils, among others. These pool types provide the necessary timing and length of inundation for Colusa grass to germinate, mature, and set seed. The Waterford Unit contains very large vernal pool complexes that will likely continue to support vernal pool ecosystem processes important to the conservation of Colusa grass. This unit contains vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Colusa grass germination, growth and reproduction, and that typically become inundated during winter rains, including, but not limited to vernal pools formed on acidic soils of alluvial fans and stream terraces along the eastern margin of the San Joaquin Valley and into the adjacent foothills.

Agricultural conversion has resulted in the extirpation of at least two documented Colusa grass occurrences in this unit. Although Colusa grass has the ability to persist with dry-land farming, dry-land farming is gradually being replaced by irrigated agriculture throughout this unit.

The Waterford Unit is bordered by the Stanislaus River to the north and the Tuolumne River to the south. The City of La Grange is located southeast of this unit. County Road J9 runs west of the unit, and Oakdale is located outside of the northwest corner. The eastern boundary extends into the low elevation foothills of the Sierra Nevada. Vernal pools in the Waterford Unit are mainly located in eastern Stanislaus County, but overlap into southwestern Tuolumne county. Approximately 0.8 ha (2 ac) of this unit are lands administered by the CDFG. The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Watershed boundaries were also used in the determination. This unit coincides with Hoover's spurge Unit 4, San Joaquin Valley Orcutt grass Unit 1, and hairy Orcutt grass Unit 4. It overlaps with Greene's tuctoria Unit 5, succulent owl's-clover Unit 2, and vernal pool tadpole shrimp Unit 13.

Unit 5, Turlock Unit, Stanislaus and Merced Counties (19,850 ha (49,049 ac))

This unit is proposed as critical habitat for Colusa grass because it supports large, playa vernal pools where the species is found (CNDDB 2002, Holland 1998). The well-known Hickman pools in Stanislaus County are located within this unit. These unusual pools provide a unique habitat for Colusa grass, as well as a number of other vernal pool species. Not only does the Hickman pool complex contain one of the largest vernal lakes in California, occupying more than 121 ha (300 ac), but it also exhibits tremendous biodiversity, including one of the largest concentrations of imperiled amphibians (Medeiros 2000). Other habitat in this unit contains the primary constituent elements essential to the conservation of Colusa grass, including soil type and deeper pools that are more likely to provide the long inundation period required for germination.

The watershed containing the Hickman Colusa grass occurrences has been breached by hundreds of acres of orchards that have been planted upstream. While most of the watershed has been managed over the years in a trust of the Fred Robinson family, the integrity of the vernal pool ecosystem is threatened by agricultural development and potential biocide pollution (Medeiros 2000). Much of the irrigated farmland habitat adjacent to the western edge of this unit was historically vernal wetlands. Intensive agriculture poses the largest threat to Colusa grass habitat in the Turlock Unit.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. The Turlock Unit is bordered by the Tuolumne River to the north and the Merced River to the south. The unit lies between the towns of La Grange and Snelling. County Road J9 runs west of the unit and the eastern edge is located in the low elevation foothills of the Sierra Nevada. Vernal pools in the Turlock Unit are located in Stanislaus and Merced counties. Approximately 61 ha (24 ac) of lands within this unit are owned by the California State Parks. This unit coincides with hairy Orcutt grass Unit 5. Portions of this unit overlap with Hoover's spurge Unit 5, vernal pool fairy shrimp Unit 21, and succulent owl's-clover Unit 3A.

Unit 6, Merced Unit, Merced and Mariposa Counties (45,641 ha (112,779 ac))

This unit is proposed as critical for Colusa grass because it contains over 40 percent of all known Colusa grass occurrences (CNDDB 2002). This unit also contains a diversity of habitats for Colusa grass, including the only locations where this species is known to occur on Keyes-Pentz, Redding, and Keyes soils (USDA 2001). Although many populations of Colusa grass have been extirpated in the past two decades, populations in the Merced Unit are among the most robust remaining (Holland 2000). The area within this unit encompasses the largest block of pristine, high density vernal pool grasslands remaining in California (Vollmar 1999). It contains habitat for three listed branchiopods, six listed plants, and a number of rare species.

The majority of the land in this unit is privately owned and is used to graze cattle. TNC is conserving three occurrences of Colusa grass through a conservation easement on the Flying M Ranch located northeast of the City of Merced. The integrity of the vernal pool complexes in eastern Merced is seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced Campus and associated development. Construction of facilities to educate and serve 25,000 UC students as well as faculty, staff, and their families within the vernal pool complexes in eastern Merced County, could have a major impact on these vernal pools. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Indirect and cumulative impacts of the proposed 1,673 ha (4,133 ac) campus and associated community may be minimized with the creation of a 2,036 ha (5,030 ac) preserve intended to protect sensitive vernal pool habitat, to be purchased with money donated by the Packard Foundation.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. A majority of the vernal pool habitat in the Merced Unit is in Merced County, although the eastern edge of the unit overlaps into Mariposa County in the low elevation foothills of the Sierra Nevada. The northern boundary parallels the Merced River, and Bear Creek serves as the southern border. The entire unit is located east of Highway 99. Approximately 419 ha (1,047 ac) of lands within this unit are owned by the USAF, 3 ha (8 ac) by BLM, and 10 ha (26 ac) by the California State Parks. The Merced Unit coincides with San Joaquin Valley Orcutt grass Unit 2, Conservancy fairy shrimp Unit 6, vernal pool fairy shrimp Unit 22, and Hoover's spurge Unit 6. It overlaps with vernal pool tadpole shrimp Unit 15, Greene's tuctoria Unit 6, and succulent owl's-clover Unit 3B.

Unit 7A and B, Grassland Ecological Unit, Madera, Merced and Stanislaus Counties (8,163 ha (20,170 ac))

This unit is proposed as critical habitat for Colusa grass because it contains vernal pools that support numerous occurrences of the species, including the only location where Colusa grass is found on clay or silty clay loam soils in the Landlow and Lewis series (Silveira in litt. 2000). The unit boundary was drawn to include these pool types, swales and associated uplands that comprise the vernal pool complexes mapped by Holland (1998) where Colusa grass is known to occur. These vernal pool complexes maintain suitable periods of pool inundation, water quality, and soil moisture for Colusa grass germination, growth and reproduction, and dispersal, but not necessarily every year (CNDDB 2001). Remaining vernal pool complexes in this unit, particularly in the eastern subunit, have been fragmented by conversion to agriculture. These areas were historically interconnected vernal pool complexes, and current efforts are underway to restore wetland habitats in this area.

The Grassland Ecological Unit includes Arena Plains and the Merced National Wildlife Refuges. We own and administer approximately 1,406 ha (3,514 ac) within this unit. Our personnel have been monitoring Colusa grass occurrences on National Wildlife Refuge lands within this unit annually since 1993. This Arena Plains and Merced NWR area contains the majority of vernal pool habitats remaining in the San Joaquin Valley and is the only location where Colusa grass occurs on the San Joaquin Valley floor. Threats to the vernal pools in this unit include agricultural conversion, changes in hydrology, invasion by aggressive plants, and inappropriate livestock grazing regimes.

The unit lies north of the City of Los Banos, southwest of the City of Merced, and is bisected by the San Joaquin River. This unit overlaps Unit 23 for vernal pool fairy shrimp and Unit 16 for vernal pool tadpole shrimp. The western half of this unit also represents Unit 6 for Hoover's spurge, and portions of Unit 7 for Conservancy fairy shrimp. In addition to the species mentioned above, vernal pool smallscale, alkali milk-vetch, western spadefoot toad, and California linderiella are present in this unit

Greene's Tuctoria

In proposing critical habitat units for Greene's tuctoria, we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are most likely to contribute to the conservation of this species and to delineate units so that threats to this species might be minimized.

Since Greene's tuctoria was first described, 19 of the 39 known occurrences (50 percent of all occurrences) have been extirpated. The other 20 occurrences are presumed to be extant, although 6 of those have not been verified for more than a decade (Alexander and Schlising 1997, CNDDB 2001). Greene's tuctoria is currently known from the Vina Plains area of Tehama and Butte counties, from portions of eastern Merced County, and from isolated occurrences in Glenn and Shasta counties (CNDDB 2001). The species is considered possibly extirpated from Fresno, Madera, San Joaquin, Stanislaus, and Tulare counties (Stone et al. 1988, Skinner and Pavlik 1994, CNDDB 2001). The areas that continue to support robust occurrences of the species include the Vina Plains area of Tehama and Butte counties, and an area in eastern Merced County. All other occurrences are considered declining and may require special management actions to ensure their long-term conservation.

One of the primary causes of extirpation for Greene's tuctoria has been conversion to irrigated agriculture; 11 of 19 (57.9 percent) extirpated occurrences were due at least in part to agricultural conversions. Stanislaus and Fresno counties experienced the greatest loss to agricultural conversion, with four and three such extirpations, respectively. Excessive livestock grazing was the sole or partial cause of extirpation for six populations (31.6 percent) (Stone et al. 1988, CNDDB 2002).

Greene's tuctoria is less tolerant of livestock grazing and competition than most of the other Orcuttieae, probably because it occurs in portions of pools that dry early in the spring. Anecdotal evidence of its lower tolerance to grazing is that Greene's tuctoria has disappeared from one grazed site where Hoover's spurge still occurs and from another site where Colusa grass remains (CNDDB 2002). Fifteen of the 20 remaining populations are subject to cattle grazing and the associated trampling, and at least 4 of those are declining (Stone et al. 1988, CNDDB 2001). Four other occurrences on the Vina Plains Preserve had been declining (Stone et al. 1988, CNDDB 2001), but improved after grazing was discontinued. Invasion from weedy plants, such as cocklebur (Xanthium sp.) and other non-native species, apparently is reducing population vigor at six localities in the Sacramento and San Joaquin valleys (Stone et al. 1988, Alexander in litt. 1998, CNDDB 2001). Agricultural conversion remains a threat to the Merced County populations, which are the only ones confirmed to be remaining in the San Joaquin Valley. Grasshoppers have been documented to consume entire populations of Greene's tuctoria before they set seed (Griggs 1980, Griggs and Jain 1983, Stone et al. 1988).

Finally, small populations of Greene's tuctoria (fewer than 100 plants) may limit persistence of several occurrences. One population in Merced County consisted of only a single plant in 1987, and one in Butte County contained 75 plants (Stone et al. 1988, CNDDB 2001). The Shasta County population also may have declined to the point where it is more vulnerable to extirpation by random events, such as fire, or by other threats as previously discussed; the Shasta County population consisted of 2,500 plants in 1993 and 1994, but declined to 120 in 1996 and 35 in 1998 despite favorable hydrological conditions. However, additional investigation of all four populations is necessary to determine whether or not larger soil seed banks exist.

Greene's Tuctoria Unit Review

We conducted a regional review across the range of Greene's tuctoria to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Modoc Plateau Unit, Lassen, and Shasta Counties (973 ha (2,403 ac))

This unit is proposed as critical habitat for Greene's tuctoria because it contains the species within Northern Basalt Flow vernal pools (CNDDB 2002) and the vernal pool habitat remains inundated for sufficient periods of time to allow Greene's tuctoria to complete its life cycle. These areas are not threatened by land conversion or development at this time due to their remote location, however, grazing activities may be contributing to the species decline in this area and may require special management actions, such as reduction or elimination of grazing, to prevent further decline and possible extirpation of the occurrence within this unit (CNDDB 2001).

Greene's tuctoria within this unit are located within an area described as a large vernal pool in an open flat in an eastside pine forest. The occurrence is located at higher elevations and has the coldest climatic conditions of any other occurrences and represents the northern extent of the species range. This unit is over 110 km (68 mi) disjunct from occurrences further south. Isolated and peripheral populations such as this may be essential to the overall long-term conservation of the species (i.e., may be genetically different from other populations in other parts of its range) (Lesica and Allendorf 1995).

The boundaries of this unit were delineated by using SPOT imagery and elevation contours to include the open flat area associated with the vernal pool including the adjacent uplands that contribute to the filling and drying of the vernal pool where Greene's tuctoria occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria to germinate and reproduce. Approximately 892 ha (2,231 ac) of this unit is owned by the USFS. The remaining lands within this unit are privately owned.

This unit for Greene's tuctoria occurs within the volcanic plateau of northeastern California. The unit is located in the area surrounding Murken Lake east of Hat Creek near Cinder Butte. Bidwell Road crosses through the southern boundary. This is the only unit where Greene's tuctoria occupies Northern Basalt Flow vernal pools. Maintaining this ecologically distinct unit is essential to the conservation of the species because it is the northern extent of its range, and is essential to maintain the diversity of habitats in which Greene's tuctoria is known to occur.

Unit 2, Vina Unit, Tehama and Butte Counties (11,673 ha (28,845 ac))

This unit is proposed as critical habitat for Greene's tuctoria because it contains occurrences of the species within vernal pools (CNDDB 2002) and the vernal pool habitat remains inundated for sufficient periods of time to allow Greene's tuctoria to complete its life cycle. This unit is proposed as critical for Greene's tuctoria because it includes 60 percent of the occurrences that are thought to be extant (CNDDB 2001). Greene's tuctoria occurs within vernal pools found on Anita and Tuscan soil series within this unit. These pool types maintain the necessary timing and length of inundation for Greene's tuctoria germination, growth, and reproduction (CNDDB 2002). This unit represents one of only two areas throughout the species range where Greene's tuctoria occurrences are not considered to be declining (CNDDB 2001).

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria germination and reproduction.

The majority of the lands included within this unit are privately owned. This unit contains TNC's 1,862 ha (4,600 ac) Vina Plains preserve. The preserve contains over 300 species of plants, and diverse communities of aquatic invertebrates. Since the 1960's, the Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating of the effects of grazing and fire on vernal pool plants, including Greene's tuctoria (Griggs 2000). Much of the basic life history information known about Greene's tuctoria was collected at Vina Plains (e.g., Stone et al. 1988, Alexander and Schlising 1997). The results of this research have provided crucial information to guide management and monitoring of vernal pool ecosystems and to identify factors which influence population dynamics of a number of endangered species, including Greene's tuctoria. The Vina Plains is open to the public and provides excellent outreach and educational opportunities. In addition to TNC, the importance of vernal pool habitats in this area has been recognized by CDFG, the Service, the EPA, the CNPS, the NRCS's WRP, and by researchers at the CSU at Chico, who have all supported research and conservation efforts for Greene's tuctoria and other vernal pool species within this unit. Urban development north of Chico and the conversion of grazed lands to more intensive agricultural uses threaten vernal pool habitat within this unit. Property ownership and protection within this unit includes CDFG (0.4 ha (1 ac)), CDFG administration (0.4 ha (1 ac)), TNC (2,295 ha (5,738 ac)), TNC easements (4,661 ha (11,653)), and WRP easements and agreements (57 ha, 142 ac)).

This unit for Greene's tuctoria occupies the area south of Toomes Creek, and north of Pine Creek and the Cana Highway. State Route 99 bisects this unit and the western boundary generally parallels the Southern Pacific Railway line. This unit is within Unit 7 for vernal pool fairy shrimp and Unit 3 for vernal pool tadpole shrimp, and encompasses part of Unit 1 for Conservancy fairy shrimp and Unit 1 for Butte County meadowfoam. The unit coincides with Unit 1 for hairy Orcutt grass, and Unit 4 for slender Orcutt grass and portions of Unit 1 for Hoover's spurge. Additional sensitive vernal pool species occurring in this unit include California linderiella and Bogg's Lake hedge-hyssop.

Unit 3, Butte Unit, Butte County (979 ha (2,418 ac))

This unit is proposed as critical habitat for Greene's tuctoria because it supports the species within large vernal pools on Tuscan soils (EPA 1994, Holland 1998, CNDDB 2002). These pools have the necessary timing and length of inundation for Greene's tuctoria germination, growth, and reproduction that typically become inundated during winter rains, but are dry during the summer. This occurrence may be threatened by overgrazing, and is described as “possibly declining” by CNDDB (2002).

Vernal pool habitats within this area have become greatly fragmented and isolated from other habitats in the region. This area is one of only four areas occupied by Greene's tuctoria in the Sacramento Valley. This area is important to maintain the geographical distribution of Greene's tuctoria through out the areas where it occurs. The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria germination and reproduction.

This unit for Greene's tuctoria occupies the area north of the intersection of State Route 99 and Route 149 in Butte County. The eastern boundary extends up the watershed of Clear Creek and the western boundary extends south paralleling State Route 99 to Little Dry Creek. This unit is within Unit 9 for vernal pool fairy shrimp and Unit 4 for vernal pool tadpole shrimp, and coincides with Unit 2 for hairy Orcutt grass and Unit 2 for Hoover's spurge. All the property within this unit is privately owned.

Unit 4, Richvale Unit, Butte County (299 ha (738 ac))

This unit is proposed as critical habitat for Greene's tuctoria because it contains occurrences of the species within vernal pools found on Rocklin and San Joaquin soils (CNDDB 2002) and the vernal pool habitat remains inundated for sufficient periods of time to allow Greene's tuctoria to complete its life cycle. This is the only area where Greene's tuctoria is found in vernal pools formed on these soil types.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria germination and reproduction.

Vernal pool habitats within this area have become greatly fragmented and isolated from other habitats. This unit is over 200 km (120 mi) from the nearest Greene's tuctoria occurrences to the south. This occurrence of Greene's tuctoria helps to maintain the species range in the Sacramento Valley. This unit for Greene's tuctoria occupies the area west of the Thermalito Afterbay near the Richvale Highway and directly west of the Oroville Wildlife Area managed by CDFG (4 ha (9ac)). The remaining property within this unit is privately owned.

Unit 5, Sacramento National Wildlife Refuge Unit, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical for Greene's tuctoria because it contains occurrences of the species within vernal pools that provide the necessary timing and length of inundation essential to the conservation of Greene's tuctoria, including alkaline vernal pools on Willows soils (Silveira 2000). Greene's tuctoria has been declining within this unit and we have taken management actions to prevent extirpation of the species from the refuge lands (Silveira 2000).

This area is one of only four areas occupied by Greene's tuctoria in the Sacramento Valley. This occurrence is important to maintain the geographical distribution of Greene's tuctoria into the unique alkali flat habitats of the Colusa Basin. The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Greene's tuctoria germination and reproduction.

This unit occurs predominantly on the Sacramento National Wildlife Refuge (5,126 ha (12,816 ac)). It is the only known location where Greene's tuctoria occurs on public land. It occurs east of Interstate 5 to the Colusa Trough from Riz Road on the north and Delevan Road on the south. Other rare vernal pool species found in the unit include pappose spikeweed, Fremont's goldfields, alkali goldfields, Scribe's popcorn flower, Hoover's downingia, folded downingia, Heckard's peppergrass, heartscale, brittlescale, San Joaquin spearscale, Ferris' milk-vetch, spike-primrose, sessile mousetail, and palmate-bracted bird's beak. This unit is also part of vernal pool fairy shrimp Unit 10, and vernal pool tadpole shrimp Unit 5, and coincides with Unit 2 for Conservancy fairy shrimp, Unit 3 for Hairy Orcutt grass, and Unit 3 for Hoover's spurge.

Unit 6, Waterford Unit, Stanislaus and Tuolumne Counties (36,414 ha (89,978 ac))

This unit is proposed as critical habitat for Greene's tuctoria because it supports occurrences of the species within vernal pools and swales that maintain the necessary primary constituent elements essential for its conservation, including the only vernal pools where Greene's tuctoria is known to occur on slightly alkaline soils of the Meikle and Paulsell series (CNDDB 2002, Holland 1998, USDA 2001). This unit contains numerous pools with occurrences and associated watersheds that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for the germination, growth, reproduction, and dispersal of Greene's tuctoria.

Agricultural conversion presents the greatest threat to habitat for Greene's tuctoria in this unit, and several occurrences within this unit have been extirpated or have severely declined as a result of agricultural conversion and intensive grazing (CNDDB 2002). This unit is over 200 km (120 mi) from the nearest Greene's tuctoria occurrences to the north. All occurrences in this unit are on private lands.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. The Waterford Unit is bordered by the Stanislaus River to the north and the Tuolumne River to the south. The City of La Grange is located southeast of the unit. County Road J9 runs west of the unit, and the Oakdale Airport is located outside of the northwest corner. The eastern boundary extends into the low elevation foothills of the Sierra Nevada. Vernal pools in the Waterford Unit are located mainly in eastern Stanislaus County, but overlap into southwestern Tuolumne County. This unit overlaps with vernal pool tadpole shrimp Unit 13, San Joaquin Valley Orcutt grass Unit 1, hairy Orcutt grass Unit 4, Colusa grass Unit 5, Hoover's spurge Unit 4, and succulent owl's-clover Unit 2. Other sensitive vernal pool species found within this unit include California tiger salamander, western spadefoot toad, dwarf downingia, and California linderiella. Approximately 0.8 ha (2 ac) of this unit is administered by the CDFG. The remaining lands within this unit are privately owned.

Unit 7, Merced Unit, Merced, Madera, and Mariposa Counties (73,707 ha (182,127 ac))

This unit is proposed as critical for Greene's tuctoria because it contains numerous occurrences of the species within large, hydrologically intact vernal pool grassland areas (Holland 1998, Vollmar 1999), including pools Northern Hardpan vernal pools on Redding, Raynor, and Bear Creek soils (USDA 2001, EIP 1999). Over 30 percent of the extant occurrences of Greene's tuctoria are in the Merced Unit (CNDDB 2001). This unit contains the primary constituent elements necessary for conservation of the species including germination, growth, reproduction, and dispersal. This unit represents one of only two areas throughout the species range where Greene's tuctoria occurrences are not considered to be declining (CNDDB 2001).

Agricultural conversion presents a great threat to habitat for Greene's tuctoria, particularly in areas along the western edge of this unit on the valley floor where irrigated agriculture has encroached on lands adjacent to occupied vernal pool complexes. The proposed UC Merced Campus and associated development will also have a significant impact on the long-term sustainability of vernal pool complexes. Other significant threats to Greene's tuctoria include urban encroachment and competition with non-native plants.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. A majority of the vernal pool habitat in the Merced Unit is in Merced County. The eastern edge of the unit overlaps into Mariposa County and in the south it extends to the Chowchilla River in Madera County. The northern boundary parallels the Merced River. The entire unit is located east of Highway 99. The Merced Unit coincides with vernal pool tadpole shrimp Unit 15 and vernal pool fairy shrimp Unit 22. It also encompasses hairy Orcutt grass Unit 6, succulent owl's-clover units 3B and 4, San Joaquin Valley Orcutt grass units 2 and 3, Colusa grass Unit 7, and Conservancy fairy shrimp Unit 6. Other sensitive vernal pool species found within this unit include the California tiger salamander, shining navarretia, dwarf downingia, Bogg's Lake hedge-hyssop, western spadefoot toad, and California linderiella. Approximately 419 ha (1,048 ac) is owned by the DOD, 3 ha (4 ac) by BLM, 10 ha (26 ac) by California State Parks. TNC has 4,513 ha (11,283 ac) of easement lands within this unit. The remaining lands within this unit are privately owned.

Unit 8, Madera Unit, Madera County (13,222 ha (32,670 ac))

This unit is proposed as critical habitat for Greene's tuctoria because the area supports occurrences of the species (CNDDB 2002). This occurrence represents the southern extent of the species currently known range. All other historical or previously documented occurrences to the south in Fresno and Tulare counties are considered extirpated (CNDDB 2002). Although this site is considered possibly extirpated, it is proposed as critical habitat until a determination of the current status of the occurrence can be made. Greene's tuctoria has a highly persistent soil seed bank, and it is likely that individuals exist in the soil as seeds even if adult plants have not been observed at the site in recent times. This unit contains areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. There are numerous wetland features that contain suitable inundation periods for Greene's tuctoria to germinate, grow, and reproduce. Vernal pools and their associated biota, particularly on the western edge of this unit closer to the valley floor, are progressively being degraded and replaced by irrigated agriculture and invasive plant species.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Located in Madera County, this unit contains vernal pool habitat extending from the Chowchilla River in the north to the Fresno River in the south. All vernal pools in this unit are located east of State Highway 99 and extend into the low elevation foothill region of the Sierra Nevada. The town of Madera borders the unit on its southwest edge, Hensley Lake is east of the unit, and Eastman Lake is northeast of the unit. The Madera Unit overlaps with succulent owl's-clover Unit 4, San Joaquin Valley Orcutt grass units 3 and 4, and hairy Orcutt grass Unit 6, and vernal pool tadpole shrimp Unit 15. Other sensitive vernal pool species found within this unit include California tiger salamander and California linderiella. All the lands within this unit are privately owned.

Hairy Orcutt Grass

In proposing critical habitat units for hairy Orcutt grass, we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of hairy Orcutt grass.

Of the 38 hairy Orcutt grass element occurrences listed by the CNDDB (2001), not counting the misidentified population of San Joaquin Valley Orcutt grass, 24 are presumed to be extant. Nineteen of those occurrences have been confirmed as extant within the past decade (CNDDB 2001). Currently, the main area of concentration for hairy Orcutt grass is the Vina Plains area in Tehama County. An isolated occurrence is found nearby in central Butte County. Several other occurrences are found in Madera County between the city of Madera and Millerton Lake. There are several occurrences in eastern Stanislaus County. All four extant occurrences in Glenn County occur on the Sacramento National Wildlife Refuge. Hairy Orcutt grass apparently has been extirpated from Merced County (Stone et al. 1988, Keeler-Wolf et al. 1998, CNDDB 2001).

Historically, habitat loss was the primary factor responsible for the decline of hairy Orcutt grass. Of the 11 element occurrences considered by the CNDDB (2002) to be extirpated, 4 in Stanislaus County were converted to almond orchards or vineyards (Stone et al. 1988, CNDDB 2002). Most of the conversion occurred prior to 1976 (Crampton 1959, Crampton 1976, Medeiros 1976, Reeder 1982). Two other occurrences in Madera County were lost by development for residences and orchards. The other five occurrences, which were in Madera, Merced, and Stanislaus counties, are listed as extirpated because the habitat was being used for irrigated pasture or dry farming or had been disced when they were last visited in 1986 and 1987 (Stone et al. 1988). However, continued field visits are advisable because another population reappeared several years after discing (CNDDB 2001).

Hairy Orcutt grass no longer occurs in the Glenn County pool where it was found in 1937 because the area is now a permanent pond (J. Silveira pers. comm.). Inappropriate hydrology also may be responsible for the loss of one other occurrence at the Sacramento National Wildlife Refuge (Silveira in litt. 2000). The population consisted of 20 plants when it was first discovered in 1993, but those plants died before setting seed due to flooding from a summer rainstorm, and none have been seen since that time (Silveira in litt. 2000). The population could reappear in future years if a substantial soil seed bank exists, and thus it is presumed to be extant.

Habitat loss continues to pose a threat to the survival of hairy Orcutt grass. Agricultural and residential development are proceeding in the vicinity of the remaining Stanislaus and Madera county occurrences and may lead to the destruction of additional populations in the foreseeable future (Stone et al. 1988). Cattle grazing was an ongoing land use at 20 occurrences when they were last visited, including 6 where this species may already be extirpated (CNDDB 2002). Three occurrences are believed to have been eliminated by “excessive” livestock grazing, and seven others were damaged by summer grazing or overuse. However, “moderate” grazing in spring likely is compatible (Stone et al. 1988) and may be beneficial. Invasion of non-native plants is an increasing problem throughout the range of hairy Orcutt grass (Stone et al. 1988). Several researchers (Stone et al. 1988, Alexander and Schlising 1997) have suggested that cattle may have carried in seeds of non-native plants, and disturbance from trampling may have facilitated their establishment. Bindweed (Convolvulus sp.) has increased in frequency in the Vina Plains since 1984, and cocklebur is still present. Pools where hairy Orcutt grass grows had higher frequencies of these invasive species than did other pools on the Vina Plains Preserve in 1995 and altered hydrology may have contributed to the presence of invasive plants in the pools (Alexander and Schlising 1997).

Hairy Orcutt Grass Unit Review

We conducted a regional review across the range of hairy Orcutt grass to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Vina Plains Unit, Tehama and Butte Counties (8,748 ha (21,617 ac))

This area is proposed as critical habitat for hairy Orcutt grass because it supports over 25 percent of all known occurrences of the species and contains large vernal pools occurring on Tuscan and Anita soils (USDA 2001, CNDDB 2002). The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for hairy Orcutt grass germination and reproduction. This unit represents the northern extent of the species range, and is over 40 km (25 mi) from the nearest occurrence to the south. This area represents one of only two areas where large hairy Orcutt populations are protected, and where long-term monitoring of the species status has occurred.

Hairy Orcutt grass may be threatened by invasive species within this unit (Alexander and Schlising 1997). In some areas special management actions have been taken to counteract the negative effects of invasive species on hairy Orcutt grass. For example, cocklebur, an aggressive native plant, has been removed by hand from some of the Vina Plains pools (Alexander and Schlising 1997), an effort that began in 1991 using funds from the California Endangered Species Tax Check-Off Fund (CDFG 1991).

The majority of the lands included within this unit are privately owned. This unit contains TNC's 1862-ha (4,600-ac) Vina Plains preserve. The preserve contains over 300 species of plants, and diverse communities of aquatic invertebrates. Since the 1960's, the Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating of the effects of grazing and fire on vernal pool plants, including hairy Orcutt grass (Griggs 2000). Much of the basic life history information known about hairy Orcutt grass was collected at Vina Plains (e.g., Stone et al. 1988, Alexander and Schlising 1997). The results of this research have provided crucial information to guide management and monitoring of vernal pool ecosystems and to identify factors which influence population dynamics of a number of endangered species, including hairy Orcutt grass.

The Vina Plains is open to the public and provides excellent outreach and educational opportunities. In addition to TNC, the importance of vernal pool habitats in this area has been recognized by the CDFG, the Service, the EPA, the CNPS, the NRCS's WRP, and by researchers at the CSU at Chico, who have all supported research and conservation efforts for hairy Orcutt grass and other vernal pool species within this unit. Urban development north of Chico and the conversion of grazed lands to more intensive agricultural uses threaten vernal pool habitat within this unit.

This unit for hairy Orcutt grass occupies the area south of Deer Creek and north of Pine Creek to near Cana Highway. State Route 99 bisects this unit and the western boundary generally parallels the Southern Pacific Railway line. This unit is included within Unit 7 for vernal pool fairy shrimp, Unit 3 for vernal pool tadpole shrimp, Unit 1 for Conservancy fairy shrimp, Unit 2 for Greene's tuctoria, Unit 1 for Hoover's spurge, and Unit 4 for slender Orcutt grass. Additional sensitive vernal pool species occurring in this unit include California linderiella and Bogg's Lake hedge-hyssop. Land ownership within this unit includes 2,264 ha (5,660 ac) by TNC and 57 ha (142 ac) of private land protected by conservation easement or agreement under the WRP. TNC has an additional 3,826 ha (9,564 ac) of conservation easements within this unit.

Unit 2, Butte Unit, Butte County, California (979 ha (2,418 ac))

This unit is proposed as critical for hairy Orcutt grass because it supports the species within vernal pools on Tuscan soils (Holland 1998, USDA 1994, 1999, CNDDB 2002). These pool types remain inundated for sufficient periods of time to allow hairy Orcutt grass to complete its life cycle. This area and Unit 1 are the only locations where hairy Orcutt grass is found on the Tuscan soil types. This area comprises one of only three areas where this species occurs in the Sacramento Valley, and is important to maintain the species range and distribution. The northern occurrences of hairy Orcutt grass are isolated from occurrences in the southern part of the species range. This unit is over 40 km (25 mi) from the nearest units to the north and west, and over 225 km (140 mi) from the nearest unit to the south and is one of seven known occurrences of the species. This unit represents some of the last remaining lower elevation vernal pool habitats in Tehama and Butte counties.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) and EPA (1994) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for hairy Orcutt grass germination and reproduction.

This unit for hairy Orcutt grass occupies the area north of the intersection of State Route 99 and Route 149 in Butte County. The eastern boundary extends up the watershed of Clear Creek and the western boundary extends south paralleling State Route 99 to Little Dry Creek. This unit is within Unit 9 for vernal pool fairy shrimp and Unit 4 for vernal pool tadpole shrimp, and coincides with Unit 3 for Greene's tuctoria and Unit 2 for Hoover's spurge. All the lands within this unit are privately owned.

Unit 3, Sacramento Refuge Unit, Glenn and Colusa Counties (5,718 ha (14,129 ac))

This unit is proposed as critical for hairy Orcutt grass because it contains multiple occurrences of the species within alkaline vernal pools on the Willows and Riz soil series (CNDDB 2002) and the vernal pool habitat remains inundated for sufficient periods of time to allow hairy Orcutt grass to complete its life cycle. This area is one of only three locations where hairy Orcutt grass is found in the Sacramento Valley. This area represents one of only two areas where large hairy Orcutt populations are protected, and where long-term monitoring of the species status has occurred.

Habitat for hairy Orcutt grass is greatly fragmented in this portion of its range, and this unit is over 40 km (25 mi) from the nearest unit to the east, and over 225 km (140 mi) from the nearest unit to the south. Hairy Orcutt grass is known from only 7 general areas across its entire range, and each of these locations is essential to the conservation of this species.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for hairy Orcutt grass germination and reproduction.

This unit for hairy Orcutt grass occupies the vernal pool habitat east of Interstate 5 to the Colusa Trough from Riz Road on the north and Delevan Road on the south. The area encompasses the Sacramento National Wildlife Refuge 5,126 ha (12,816 ac). This unit is also part of vernal pool fairy shrimp Unit 10, and vernal pool tadpole shrimp Unit 5, and coincides with Unit 2 for Conservancy fairy shrimp, Unit 5 for Greene's tuctoria, and Unit 3 for Hoover's spurge. Other rare vernal pool species found in the unit include pappose spikeweed, Fremont's goldfields, alkali goldfields, Scribe's popcorn flower, Hoover's downingia, folded downingia, Heckard's peppergrass, heartscale, brittlescale, San Joaquin spearscale, Ferris' milk-vetch, spike-primrose, sessile mousetail, and palmate-bracted bird's beak. The remaining land within this unit is privately owned.

Unit 4, Turlock Unit, Stanislaus and Merced Counties (25,318 ha (62,560 ac))

The Turlock Unit is proposed as critical habitat for hairy Orcutt grass because it contains occurrences of the species within large vernal pools on Whitney and Meikle soils that provide the necessary timing and length of inundation essential to the conservation of this species (CNDDB 2001, Holland 1998, USDA 2001). This unit contains the well known Hickman pools in Stanislaus County, and a high concentration of hairy Orcutt grass occurrences (CNDDB 2001). The Hickman pool complex contains one of the largest vernal lakes in California at more than 121 ha (300 ac) and represents a unique habitat for hairy Orcutt grass. This unit contains numerous vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths to sustain hairy Orcutt grass germination, growth, and reproduction.

This unit contains large, intact vernal pool grasslands that help maintain the distribution of the species over its entire range. In vernal pool grasslands south of this unit, two hairy Orcutt grass occurrences are presumed extirpated as a result of agricultural conversion and intensive cattle grazing. Extant hairy Orcutt grass occurrences within this unit are threatened by altered hydrology, overgrazing, and competition with invasive species (CNDDB 2002). The watershed containing the Hickman vernal pools has been breached by hundreds of acres of orchards that have been planted upstream. The integrity of the vernal pool complexes in eastern Stanislaus and Merced counties is seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced Campus and associated development.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. The Turlock Unit is bordered by the Tuolumne River to the north and the Merced River to the south. The unit lies between the towns of La Grange and Snelling. County Road J9 runs west of the unit and the eastern edge is located in the low elevation foothills of the Sierra Nevada. Vernal pools in the Turlock Unit are located in eastern Stanislaus and Merced counties. This unit coincides with Hoover's spurge Unit 5, Colusa grass Unit 7, Greene's tuctoria Unit 9 and succulent owl's-clover Unit 3A. It overlaps vernal pool fairy shrimp Unit 21. Land ownership within this unit includes BLM (7 ha (17 ac)) and California State Parks (25 ha (61 ac)). The remaining land within this unit is privately owned.

Unit 5, Madera Unit, Madera County (9,085 ha (22,448 ac))

This unit is proposed as critical habitat for hairy Orcutt grass because it contains occurrences of the species within vernal pools formed on Greenfield and Hanford soil series (Holland 1998, CNDDB 2002). These soils support vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths to sustain germination, growth and reproduction of hairy Orcutt grass. To maintain the full range of ecological conditions in which this species occurs, conservation of hairy Orcutt grass populations and vernal pool habitat in the Madera Unit is important.

The Madera Unit contains a California Department of Transportation mitigation site which protects a small occurrence of hairy Orcutt grass, and is the only conservation area for this species in the Southern Sierra Foothills. However, vernal pool habitat in and adjacent to this unit is progressively being eliminated and modified. An occurrence of hairy Orcutt grass approximately 11 km (7 mi) east of Madera has been extirpated due to residential development. The development of ranch-style homes, small horse pastures, orchards and new roads poses a serious threat to at least five other occurrences in or adjacent to this unit. However, hairy Orcutt grass has successfully been introduced into created vernal pools in this unit.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Located in Madera County, this unit contains vernal pool habitat extending from the Chowchilla River in the north to the Fresno River in the south. The Fresno River separates this unit from the Cottonwood Creek Unit to the south. All vernal pools in this unit are located east of the Atchison, Topeka, and Santa Fe Railroad and extend into the low elevation foothill region of the Sierra Nevada. Berenda Creek bisects the unit. The town of Madera is located southwest of the unit, Hensley Lake is east of the unit, and Eastman Lake is northeast of the unit. The Madera Unit coincides with San Joaquin Valley Orcutt grass Unit 4, succulent owl's-clover Unit 4, and overlaps vernal pool fairy shrimp Unit 24A. Other sensitive vernal pool species found within this unit include California tiger salamander and California linderiella. All the land within this unit is privately owned.

Unit 6, Cottonwood Creek Unit, Madera County (15,824 ha (39,100 ac))

This area is proposed as critical habitat for hairy Orcutt grass because it supports over 15 percent of the known occurrences of the species within Northern Claypan vernal pools formed on Cometa, Greenfield, Hanford soil series (CNDDB 2001, USDA 1994, Holland 1998). These pool types provide the necessary timing, length of inundation, water quality, and soil moisture for hairy Orcutt grass germination, growth and reproduction. The Cottonwood Creek Unit represents the southern extent of hairy Orcutt grass range. This unit contains large intact and contiguous vernal pool grassland areas that help maintain the distribution of the species through out its range.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. Located in Madera County, this unit contains vernal pool habitat extending from the Fresno River in the north to the San Joaquin River in the south. The Fresno River separates this unit from the Madera Unit to the north. All vernal pools in this unit are located east of the Atchison, Topeka, and Santa Fe Railroad, extending east into the low elevation foothill region of the Sierra Nevada. Highway 41 bisects the eastern portion of the unit. The Cottonwood Creek Unit overlaps succulent owl's-clover Unit 4, San Joaquin Valley Orcutt grass Unit 4, and vernal pool fairy shrimp Unit 24A. Other sensitive vernal pool species found within this unit include California linderiella, spiny-sepaled button-celery, California tiger salamander, and western spadefoot toad. Approximately 4 ha (10 ac) are owned by the CDFG.

Sacramento Orcutt Grass Criteria

In proposing critical habitat units for Sacramento Orcutt grass we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation of Sacramento Orcutt grass.

Sacramento Orcutt grass is found only in Sacramento County. The species was historically known from nine occurrences. However, one entire occurrence and a portion of another have been extirpated. Thus, eight of the nine occurrences are extant. Five occurrences, comprising more than 70 percent of the occupied habitat, are concentrated into a single area of approximately 6 sq km (2.3 sq mi) east of Mather Field. Two other occurrences are adjacent to each other—Phoenix Field Ecological Reserve and the introduced population at Phoenix Park. The eighth extant occurrence is near Rancho Seco Lake (Stone et al. 1988, Cochrane in litt. 1995a, Morey in litt. 1996, CNDDB 2002).

Sacramento Orcutt grass was extirpated from its historic occurrence between Orangevale and Folsom by urban development. The species was extirpated from one pool near Grant Line Road by changes in hydrology—pool depth was increased artificially to provide a longer-lasting water source for livestock, which created conditions unsuitable for persistence of Sacramento Orcutt grass (Stone et al. 1988, CNDDB 2002). Even though they have not been extirpated, extant occurrences at the Phoenix Field Ecological Reserve and the Phoenix Park Vernal Pool Preserve have been degraded by off-road vehicles and alterations to natural drainage patterns (Clark et al. 1998).

The remaining pools where Sacramento Orcutt grass grows are subject to a wide variety of factors that threaten the species survival. Urban encroachment and the associated increase in human activities, is the primary factor. One occurrence in the primary area of concentration could be destroyed by expansion of the county landfill (Cochrane in litt. 1995a); the precise area of expansion has yet to be determined. At present, trash from the landfill frequently blows into the pools (Cochrane in litt. 1995b). An industrial park and road widening threaten another one of the occurrences in the same area (Stone et al. 1988, Cochrane in litt. 1995a).

Competition from native plants such as pale spikerush (Heleocharis sp.) and mannagrass (Glyceria sp.) could displace Sacramento Orcutt grass (Stone et al. 1988, Cochrane in litt. 1995a, Cochrane in litt. 1995b, Clark et al. 1998). Livestock grazing during the growing season, or overstocking during winter grazing, may degrade habitat for Sacramento Orcutt grass; however, grazing may be useful in providing control of competing plants if appropriate timing and stocking rates can be determined (Griggs 1977, Stone et al. 1988, Cochrane in litt. 1995b).

Sacramento Orcutt Grass Unit Review

We conducted a regional review across the range of Sacramento Orcutt grass to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Phoenix Field and Phoenix Park Unit, Sacramento County (29 ha (72 ac))

This unit is proposed as critical habitat for Sacramento Orcutt grass because it supports 25 percent of the known occurrences (2 of 8), including occurrences found within vernal pools on Red Bluff and Redding soils (CNDDB 2002). These pool types provide the necessary timing and frequency of inundation for Sacramento Orcutt grass germination, growth, and reproduction. The unit boundary was drawn to include Sacramento Orcutt grass and the vernal pool complexes in which it occurs (Holland 1998, Sacramento County 1999). SPOT imagery was used to exclude urban and developed areas, however, the resolution of this imagery did not permit us to exclude all developed areas. This unit represents the northern extent of the species range, and one of only three areas where Sacramento Orcutt grass is known to occur.

The Phoenix Field Ecological Reserve and Phoenix Park occurrences are affected by excess runoff from lawns, baseball fields, and roads; by herbicide and fertilizer applied in adjacent areas (Griggs and Jain 1983, Holland in litt. 1986, Stone et al. 1988, Cochrane in litt. 1995a, Morey in litt. 1996, Clark et al. 1998); and by dumping of landscape waste (Clark et al. 1998). Another threat at the Phoenix Field Ecological Reserve is invasion of garden plants (Clark et al. 1998). Recreational activities such as rollerblading (Witham in litt. 2000a), biking, and horseback riding (Cochrane in litt. 1995a, Cochrane in litt. 1995b, Clark et al. 1998) also are damaging the Phoenix Park occurrence.

This unit is situated within the City of Fair Oaks, and lies east of Hazel Avenue and northwest of Lake Natoma. This unit is bounded by urban development except for the east side, which is adjacent to Folsom Lake State Recreation Area. The City of Fair Oak's Phoenix Park, Phoenix Field, and Jim David Park are included within the boundaries of this unit. The unit consists primarily of public land and is frequently visited by the public. Although surrounded by development, this unit represents an important urban preserve for the species.

Unit 2, Southeast Sacramento Valley Unit, Rancho Cordova, Sacramento County (8,853 ha (21,875 ac))

This unit is proposed as critical habitat for Sacramento Orcutt grass because it contains over 50 percent of the known occurrences (4 of 8) of the species within vernal pools on Redding and Redbluff soils that contain the primary constituent elements essential for the conservation of the species (USDA 2001, Holland 1998, Sacramento County 1999, CNDDB 2002). This unit also represents one of only three units for the species across its entire range. This unit includes relatively undisturbed, hydrologically intact vernal pool habitats as mapped by Holland (1998), that may continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for Sacramento Orcutt grass to complete germination and reproduction.

The Southeastern Sacramento Valley Unit for Sacramento Orcutt grass occupies the area south and east of Mather Airport and Regional Park. The Cosumnes River forms part of the southern and eastern boundary of the unit. Urban areas in the cities of Sacramento and Rosemont form the western boundary. Mather Airport and the dredge tailings northeast of the airport form the northern boundary. The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for Sacramento Orcutt grass germination and reproduction.

The majority of the lands included within this unit are privately owned, including the Sunrise Douglas mitigation area, where several occurrences of Sacramento Orcutt grass are known to occur. Other vernal pool habitats in this area have been identified by the Sacramento Valley Open Space Conservancy, the CNPS, and TNC as excellent examples of vernal pool grasslands, supporting a rich and diverse community of vernal pool endemic plants and animals within Sacramento County. Vernal pool habitats in this unit are threatened by urbanization from the expanding cities of Sacramento and Elk Grove. Conversion to intensive agriculture, particularly vineyards, is also a significant threat to Sacramento Orcutt grass habitat in this unit. The unit is bisected by the Folsom South Canal and State Highway 16. This unit is included in Unit 8 for vernal pool tadpole shrimp and Unit 13 for vernal pool fairy shrimp and coincides with Unit 6 for slender Orcutt grass. Other sensitive vernal pool species located within this unit include California linderiella, legenere, Bogg's Lake hedge-hyssop, Ahart's dwarf rush, and western spadefoot toad.

Unit 3, Rancho Seco Unit, Sacramento and Amador Counties (15,750 ha (38,918 ac))

This unit is proposed as critical habitat for Sacramento Orcutt grass because it supports occurrences of the species within high terrace vernal pools on Corning soils that contain the primary constituent elements and provide the necessary timing and frequency of ponding that allow the species to germinate and reproduce (Holland 1998, USDA 2001, Sacramento County 1999, CNDDB 2002). This unit represents one of only three areas where this species is known to occur, and is the southern extent of the species range. All of these areas are essential to the species by improving its chances of surviving natural and environmental changes, as well as random or stochastic events. This unit includes relatively undisturbed, hydrologically intact vernal pool habitats, that may continue to support natural vernal pool ecosystem processes and maintain suitable habitat conditions for the species.

The western boundary of the unit was defined by the extent of high terrace soils in the region, including Corning and Redding soils, which generally comprise the extent of Sacramento Orcutt grass habitat. The northern and southern boundaries of this unit were delineated to exclude urban and agricultural areas. The majority of land within this unit is privately owned. Some vernal pool areas are protected in this unit on TNC's Howard Ranch Preserve and Schnider property near Meiss Road. The Clay Station Mitigation Bank and the Borden Ranch mitigation site are located within this unit, as well as a number of smaller conservation areas including the Rancho Seco Preserve and the L.V. Island Preserve. Approximately 247 ha (610 ac) is owned by the CDFG, and 3,094 ha (7,736 ac) by TNC. An additional 5 ha (11 ac) of private land is protected by WRP easements or agreements. Urban expansion and conversion to vineyards threaten existing vernal pool habitats throughout this unit.

This unit occupies the area south of Laguna Creek and north of the Sacramento and San Joaquin county line along Dry Creek. The eastern boundary is the low elevation foothills of western Amador County. The western limit is bounded by urban and agricultural areas near the cities of Galt and Elk Grove and along the foothill region of the southeastern Sacramento Valley. This unit is a portion of Unit 13 for vernal pool tadpole shrimp and Unit 19 for vernal pool fairy shrimp. Other sensitive species found within this unit include Bogg's Lake hedge-hyssop, Ahart's dwarf rush, Henderson's bent grass, legenere, Sanford's arrowhead, pincushion navarretia, dwarf downingia, California tiger salamander, western spadefoot toad, and California linderiella.

San Joaquin Valley Orcutt Grass Criteria

In proposing critical habitat units for San Joaquin Valley Orcutt grass we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are most likely to contribute to the conservation of this species.

San Joaquin Valley Orcutt grass is restricted to the foothills of the southern Sierra foothill region of the San Joaquin Valley. Of the 47 occurrences of San Joaquin Valley Orcutt grass ever reported, 27 are presumed to be extant; 17 are certainly extirpated and 3 others are possibly extirpated because the habitat has been modified (CNDDB 2001). However, only 12 of the occurrences presumed extant have been revisited within the past decade, so even the most recent information is outdated. This species has been completely extirpated from Stanislaus County but remains in Fresno, Madera, Merced, and Tulare counties (Stone et al. 1988, CNDDB 2001).

San Joaquin Valley Orcutt grass does not occur outside of the Southern Sierra Foothills Vernal Pool Region (Keeler-Wolf et al. 1998). The primary area of concentration is northeast of Merced in Merced County, with 14 occurrences (52 percent) on the Flying M Ranch and adjacent lands (EIP Associates 1999, Witham in litt. 2000b, CNDDB 2001). The Lanes Bridge area of Madera and Fresno counties has the second highest concentration of San Joaquin Valley Orcutt grass, with seven occurrences (26 percent), including the introduced population. The remaining six occurrences include three in the Le Grand area of Merced County, two on the tabletops near the San Joaquin River in Madera and Fresno counties, and one in northwestern Tulare County (Stone et al. 1988, Stebbins et al. 1995, CNDDB 2001).

All of the habitat of San Joaquin Valley Orcutt grass in Stanislaus County and much of that in Madera and Fresno counties has been converted to irrigated agriculture, especially to almond orchards and vineyards (Stone et al. 1988, CNDDB 2001). The majority of sites were converted by the late 1970's (Griggs 1980, Griggs and Jain 1983). Altered hydrology and development (residential, commercial, and recreational) eliminated several other populations (Stone et al. 1988, CNDDB 2001). Dryland grain farming has modified vernal pool habitats of San Joaquin Valley Orcutt grass in Madera and Merced counties, and the species is presumed to be extirpated from those occurrences (CNDDB 2001). However, Crampton (1959, 1976) indicated that San Joaquin Valley Orcutt grass could persist despite dryland farming, and the species was rediscovered at one such site after having been absent for several years (CNDDB 2001). Summer livestock grazing or heavy use by cattle damaged two populations each in Madera and Merced counties (Stone et al. 1988, CNDDB 2001); their current status is not known.

The primary threats facing the remaining occurrences of San Joaquin Valley Orcutt grass are altered livestock grazing regimes, agricultural conversion, and small population size (Stone et al. 1988, CNDDB 2001). Most extant populations are grazed currently. According to Stone et al. (1988), moderate cattle grazing in spring is compatible with persistence of San Joaquin Valley Orcutt grass, and possibly beneficial, but increased stocking rates or summer or year-round grazing would be detrimental. Conversion to irrigated agriculture is most likely at sites that currently are dry-farmed. Small populations are at risk of extirpation due to chance events (Menges 1991), particularly those that fluctuate greatly from year to year (Thomas 1990). Omitting those described only as “abundant,” population size has been estimated for 14 occurrences of San Joaquin Valley Orcutt grass. Three numbered fewer than 10 plants each, even in favorable years (Stone in litt. 1992, Stebbins et al. 1995, CNDDB 2001).

Additional threats to San Joaquin Valley Orcutt grass are varied. Four of the extant occurrences in Madera County are in the path of the proposed extension of State Highway 41 (Stone in litt. 1992). Three other occurrences in Madera and Fresno counties are threatened by a proposed residential development (Stone et al. 1988, Stebbins et al. 1995, CNDDB 2001). One occurrence could be destroyed by construction of the proposed UC campus in Merced County (EIP Associates 1999). Altered hydrology, competition from other plants, and off-road vehicles are potential threats at a few sites (Stone et al. 1988). Foraging by grasshoppers (family Acrididae) and mice (order Rodentia) occasionally poses problems (Stebbins et al. 1995, CNDDB 2001). In some years, grasshoppers (family Acrididae) consumed entire populations of San Joaquin Valley Orcutt grass before they set seed (Griggs and Jain 1983, Stone et al. 1988).

San Joaquin Valley Orcutt Grass Unit Review

We conducted a regional review of the known range of San Joaquin Valley Orcutt grass to evaluate and select areas that are essential to the conservation of San Joaquin Valley Orcutt grass and that may require special management. Important factors we considered were the presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Merced Unit, Merced and Mariposa Counties (45,643 ha (112,783 ac))

This unit is proposed as critical habitat for San Joaquin Valley Orcutt grass because it supports over half of the known occurrences of the species (CNDDB 2001). This unit contains the only area where San Joaquin Valley Orcutt grass is found on vernal pools formed upon Corning and Greenfield soils, and one of only two sites where it is found on San Joaquin soils (Holland 1998, USDA 2001, EIP 1999). These pool types maintain the timing and length of inundation necessary for San Joaquin Orcutt grass germination, growth, and reproduction, and provide a diversity of habitats for the species. This unit supports some of the largest, most robust occurrences of the species (Holland 2000). The area within this unit encompasses the largest block of pristine, high density vernal pool grasslands remaining in California (Vollmar 1999).

A majority of the land in the Merced Unit is privately owned and is used to graze cattle. Two occurrences on the Flying M Ranch are protected under a conservation easement with TNC. The integrity of the vernal pool complexes in eastern Merced is seriously threatened by irrigated agriculture, upland housing development, and the proposed UC Merced Campus and associated development. Construction of facilities to educate and serve twenty-five thousand UC students as well as faculty, staff, and their families within what is now high quality vernal pool habitat in eastern Merced County could have a major impact on species endemic to vernal pools. However, the recent draft biological opinion for the UC Merced campus and community developed environmental parameters which should reduce impacts to vernal pool habitats. Indirect and cumulative impacts of the proposed 1,673 ha (4,133 ac) campus and associated community may be minimized with the creation of a 2,036 ha (5,030 ac) preserve intended to protect sensitive vernal pool habitat, to be purchased with money donated by the Packard Foundation. Approximately 419 ha (1,048 ac) of this unit is owned by the DOD, 4 ha (8 ac) by BLM, 10 ha (26 ac) by California State Parks. TNC has 3,424 ha (8,559 ac) of easement lands within this unit. The remaining lands within this unit are privately owned.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. A majority of the vernal pool habitat in the Merced Unit is in Merced County, although the eastern edge of the unit overlaps into Mariposa County in the low elevation foothills of the Sierra Nevada. The northern boundary parallels the Merced River, and Bear Creek serves as the southern border. The entire unit is located east of State Highway 99. The Merced Unit coincides with vernal pool tadpole shrimp Unit 15 and vernal pool fairy shrimp Unit 22. It also overlaps hairy Orcutt grass Unit 6, Greene's tuctoria Unit 7, succulent owl's-clover Unit 3B, Colusa grass Unit 6, and Conservancy fairy shrimp Unit 6. Other sensitive vernal pool species found within this unit include the California tiger salamander, shining navarretia, dwarf downingia, Bogg's Lake hedge-hyssop, western spadefoot toad, and California linderiella.

Unit 2, Le Grand Unit, Merced, Mariposa, and Madera Counties (21,495 ha (53,114 ac))

This unit is proposed as critical habitat for San Joaquin Valley Orcutt grass because it supports occurrences of the species within vernal pools formed on alluvial terraces on Raynor clay soils (CNDDB 2001). The Le Grand Unit is essential for the conservation of San Joaquin Valley Orcutt grass because it contains large intact and contiguous vernal pool grassland areas that provide connectivity between units to the north and south. This unit contains vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain San Joaquin Orcutt grass germination, growth, reproduction, and dispersal. This unit is important to maintain the range of habitats in which the species is known to occur.

This unit contains an area where San Joaquin Valley Orcutt grass was introduced into six created pools; it germinated and flowered in five of them during the 2 years following its introduction (Durgarian 1995, Stebbins et al. 1995) and was still present in 2000 (Faubion in litt. 2000). This site is now treated as an occurrence by the CNDDB (2001). The Madera Irrigation District manages the property, which is owned by the BOR (Stebbins et al. 1995). The integrity of vernal pool complexes and their associated watersheds in the Le Grand Unit is threatened by altered hydrology, competition from other plants, irrigated agricultural conversion, particularly orchards and vineyards, and urban encroachment. Several occurrences in this unit have been extirpated as a result of intensive agriculture.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. A majority of the vernal pool habitat in the Le Grand Unit is in Merced County. The eastern edge of the unit overlaps into Mariposa County and in the south it extends to the Madera County line. Bear Creek serves as the northern boundary. The entire unit is located east of State Highway 99. The towns of Le Grand and Planada are adjacent to the western edge of the unit. The Le Grand Unit overlaps with vernal pool tadpole shrimp Unit 15, Greene's tuctoria Unit 6, Conservancy fairy shrimp Unit 6, and succulent owl's-clover Unit 6. Other sensitive vernal pool species found within this unit include California tiger salamander, shining navarretia, and western spadefoot toad. TNC has 428 ha (1,070 ac) of easement lands within this unit. The remaining lands within this unit are privately owned.

Unit 3, Madera Unit, Madera County (20,937 ha (51,733 ac))

This unit is proposed as critical habitat for San Joaquin Valley Orcutt grass because it supports occurrences of the species within alluvial terrace vernal pools that provide the necessary timing and length of inundation for San Joaquin Valley Orcutt grass germination, growth, and reproduction (CNDDB 2001). This area is the only location where the species is found on Cometa and San Joaquin soils (USDA 2001).

San Joaquin Valley Orcutt grass is known from only eight general areas along the eastern margin of the San Joaquin Valley. Historically, vernal pools spanned from the low elevation Sierra Nevada foothills to the valley floor where they connected with other large vernal pool complexes. Today, only a fraction of the vernal pool habitat that was historically in the greater watershed area remains. The integrity of vernal pool complexes and their associated watersheds in the Madera Unit is threatened by altered hydrology, competition from other plants, irrigated agricultural conversion, particularly orchards and vineyards, and urban encroachment.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Located in Madera County, this unit contains vernal pool habitat south of the Chowchilla River and abutting the Fresno River. Berenda Creek is located northwest of the unit. Habitat within this unit is located east of the Atchison, Topeka, and Santa Fe Railroad and extends into the low elevation foothill region of the Sierra Nevada. The town of Madera borders the unit on its southwest edge, Hensley Lake is east of the unit, and Eastman Lake is northeast of the unit. The Madera Unit coincides with hairy Orcutt grass Unit 7, Greene's tuctoria Unit 7, succulent owl's-clover Unit 4 and vernal pool fairy shrimp Unit 24A. Other sensitive vernal pool species found within this unit include California tiger salamander and California linderiella. All the land within this unit is privately owned.

Unit 4, Fresno Unit, Fresno County (3,233 ha (7,990 ac))

This unit is proposed as critical habitat for San Joaquin Valley Orcutt grass because it contains occurrences of the species growing within vernal pools formed on Fallbrook, Ramona, San Joaquin, Vista, and Pollasky soil series (CNDDB 2002). This unit contains vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain San Joaquin Orcutt grass germination, growth, and reproduction. This unit is significant geographically, as it may contribute to dispersal to vernal pool habitats north and south of it. The diversity of vernal pool types found within the Fresno Unit contributes to the range of ecological conditions in which San Joaquin Valley Orcutt grass occurs.

Due to edaphic variation, vernal pool habitat in this unit is less dense than habitat in units further north. Vernal pools within this unit have been destroyed by conversion to irrigated agriculture, as well as urban encroachment from the cities of Fresno and Clovis. Several known occurrences of San Joaquin Valley Orcutt grass within this unit have been extirpated due to either hydrologic modifications off-site, or land use modifications such as leveling of “hog wallows” for urban development such as near State Route 41 near Woodward Park in Fresno.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery. Located in Fresno County, this unit contains vernal pool habitat south of Millerton Lake and east of the San Joaquin River. The unit is located north of Copper Road and the city of Fresno is southwest of the unit. The eastern boundary parallels the low elevation foothill region of the Sierra Nevada. Auberry Road is east of the northern portion of the unit and passes through the southern portion of the unit. CDFG has approximately 0.4 ha (1 ac) of land within this unit. The Fresno Unit overlaps San Joaquin Valley Orcutt grass Unit 5 and vernal pool fairy shrimp Unit 24B. Other sensitive vernal pool species found within this unit include California linderiella, California tiger salamander, and western spadefoot toad.

Unit 5 A and B, Table Mountain Unit, Fresno and Madera Counties, (1,723 ha (4,258ac))

This area is proposed as critical habitat for San Joaquin Valley Orcutt grass because it supports occurrences of the species within Northern Basalt Flow vernal pools (Holland 1998, Keeler-Wolf et al. 1998, CNDDB 2002). This is the only area where San Joaquin Valley Orcutt grass is known to occur within these pool types (CNDDB 2001). Northern Basalt Flow vernal pool complexes are an extremely rare vernal pool habitat occurring only on ancient terraces and hilltops above the surrounding low-lying terrain. They typically contain small, irregularly clustered pools with “flashy hydrology” (Keeler-Wolf et al. 1998). The Kennedy Table occurrence of San Joaquin Valley Orcutt grass was described as containing millions of plants in 1995 (CNDDB 2001).

This unit contains protected lands at the Big Table Mountain Ecological Reserve. A cooperative group consisting of CDFG, California Department of Parks and Recreation, Sierra Foothill Conservancy, BLM, and BOR has developed a management and monitoring plan for Big Table Mountain. BLM owns approximately 15 ha (370 ac) of land and TNC has 260 ha (650 ac) of conservation easements within this unit. Initial efforts will focus on grazing as a means to control non-native grasses while comparing population trends of threatened and endangered species in grazed and ungrazed portions of the tableland (Griggs in litt. 2000a). This unit also contains an occurrence of San Joaquin Valley Orcutt grass that is partially on public land administered by the BLM. The pool supports the second-largest population of the species known to be extant. The BLM and conservation groups are hoping to acquire the adjacent land to protect the entire pool (CNDDB 2001).

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. Unit 5 for San Joaquin Orcutt grass is comprised of two subunits. Both subunits are located east of Millerton Lake on basalt mesas above the San Joaquin River. Subunit 5B is located on Kennedy Table in Madera County, and Subunit 5A is directly south of this unit across the San Joaquin River on Table Mountain in Fresno County. The Table Mountain Rancheria is south of this unit. Unit 5 coincides with vernal pool fairy shrimp Unit 25, vernal pool tadpole shrimp Unit 17, and succulent owl's-clover units 6A and 6B. Other sensitive vernal pool species found within this unit include Bogg's lake hedge-hyssop and California linderiella.

Unit 6A and B, Tulare Unit, Tulare County (8,028 ha (19,836 ac))

This unit is proposed as critical for San Joaquin Valley Orcutt grass because it contains occurrences of the species within vernal pools on Madera and Greenfield soils that provide the primary constituent elements essential to the conservation of the species (USDA 2001, CNDDB 2001). This unit represents the southern extent of San Joaquin Valley Orcutt grass range. San Joaquin Valley Orcutt grass occurs on CDFG land at Sequoia Fields Ecological Reserve (199 ha, (491 ac)); however, most of the area within this unit is privately owned. This unit contains vernal pools and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain San Joaquin Valley Orcutt grass germination, growth and reproduction. Agricultural conversion of range or barren land and urban development have greatly reduced the amount of vernal pool habitat in this area.

The unit boundary was drawn to include species occurrences and the vernal pool complexes in which they occur as mapped by Holland (1998) and as visible on SPOT imagery, as well as elevation contours in the eastern foothill region and sub-watershed boundaries. There are two subunits within the Tulare Unit. This westernmost subunit, subunit A, is located east of J19. Road 63 cuts through its eastern edge. St. Johns River is south of the subunit and the Southern Pacific Railroad runs northeast of the unit. Subunit B is located east of Road 63 and Road 201 passes through it. It extends into the low elevation foothills of the Sierra Nevada. Colvin Mountain is located within the southwest boundary. Road 245 bisects subunit B and the south side of Red Mountain is within the northeast boundary of this unit. The Tulare Unit coincides with Hoover's spurge Unit 7, and it overlaps with vernal pool tadpole shrimp Unit 18 and vernal pool fairy shrimp Unit 26. Other sensitive vernal pool species found within this unit include California tiger salamander, spiny-sepaled button-celery, and the western spadefoot toad.

Slender Orcutt Grass Criteria

In proposing critical habitat units for slender Orcutt Grass we evaluated the life history and current distribution of the species described in the background section of this rule, the primary constituent elements described in the primary constituent element section of this rule, and the current threats to the species described below. This information allowed us to determine which areas are likely to contribute to the conservation of this species and to delineate units so that threats to this species might be minimized.

Slender Orcutt grass is currently known from 79 occurrences, of which 73 are presumed to be extant (Corbin in litt. 1999, CNDDB 2001); occurrences are presumed to be extant until the CNDDB receives documentation that they have been extirpated. The primary area of concentration for slender Orcutt grass is in the vicinity of Dales, Tehama County. A secondary area of concentration for slender Orcutt grass is the Modoc Plateau Vernal Pool Region in Lassen, Plumas, Shasta, and Siskiyou counties. Additional occurrences of the species are found in Shasta, Lake, and Sacramento counties.

Urban development in the vicinity of Redding has extirpated or caused the severe decline of five slender Orcutt grass occurrences through construction activities and hydrological alterations (Griggs and Jain 1983, CNDDB 2001). Agricultural conversion apparently eliminated the species from the type locality. Although the exact location of the type collection is not known, the general area was being used for crop fields and both irrigated and dry pastures as of 1987 (Stone et al. 1988). Urban development is continuing in the vicinity of Redding and could eliminate the remaining populations in that area.

A variety of other factors are contributing to the continued decline of slender Orcutt grass including off-road vehicle use, inappropriate livestock grazing, altered hydrology, and competition from other plants (Stone et al. 1988, Corbin and Schoolcraft 1989). Off-road vehicle use is a particular problem near Redding and in forested areas of the Modoc Plateau. According to Stone et al. (1988), “moderate” livestock grazing in spring is compatible with slender Orcutt grass but overstocking, summer grazing, and trampling pose threats to several occurrences. However, grazing may be necessary to control aggressive competitors such as the native species, pale spikerush (Witham in litt. 2000a). Altered hydrology contributes to the decline of slender Orcutt grass by creating conditions unsuitable for its germination, growth, or reproduction, and by promoting the growth of competing plant species.

Slender Orcutt Grass Unit Review

We conducted a regional review across the range of slender Orcutt grass to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1 A, B, C, D, E, F, G, H, and I, Modoc Plateau Unit, Plumas, Lassen, Shasta, Modoc, and Siskiyou Counties (23,266 ha (57,490 ac))

This unit is proposed as critical habitat for slender Orcutt grass because it contains almost 25 percent of all known occurrences of the species and the vernal pool habitat remains inundated for sufficient periods of time to allow slender Orcutt grass to complete its life cycle. The species is found growing within Northern Basalt Flow vernal pools occurring on Gooval, Lasvar, Lasvar-Pitvar, and Nosoni soils that provide the primary constituent elements essential to the conservation of the species (CNDDB 2002). These occurrences are all found on the Modoc Plateau, where they are located at higher elevations, and experience the coldest climatic conditions of any other areas throughout the species range. The occurrences are on Northern Basalt Flow vernal pools (CNDDB 2002). This area represents the northern-most extent of the range of slender Orcutt grass, and is over 50 km (32 mi) from the nearest occupied areas to the south.

The boundaries of this unit were delineated by using SPOT imagery and elevation contours to include the open flat area associated with the vernal pool including the adjacent uplands that contribute to the filling and drying of the vernal pool where slender Orcutt grass occurs. The unit designates an area sufficient to maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass to germinate, grow, and reproduce.

The Modoc Plateau area is not threatened by urban development at this time due to its remote location, however off-road vehicle use and overgrazing may threaten some occurrences in this area (CNDDB 2001). Additional sensitive species found within this unit include Bogg's Lake hedge-hyssop, and profuse flowered pogogyne (Pogogyne floribunda). Although the majority of land within this unit is located either on USFS (15,500 ha (38,750 ac)), NPS (58 ha (144 ac)), or BLM lands (2,754 ha (6,886 ac)). The California State Parks also has land within this unit (37 ha (92 ac)).

This unit for slender Orcutt grass consists of nine subunits largely within the volcanic plateau of northeastern California. The nine subunits are identified as the Lake Almanor, Crater Lake Mountain, Poison Lake, Badger Mountain, Lost Creek, Goose Valley, Long Valley, Cayton Creek, and Timbered Crater subunits. The Lake Almanor subunit is located in Plumas County, on the southwestern part of Lake Almanor along Humbug Humboldt Cross Road and State Route 89. The area extends from near the shoreline upslope to the watershed boundary. The land is owned by the USDA and managed by the USFS. The Crater Lake Mountain subunit is located along Route 44 and encompasses the northwestern portion of Crater Lake Mountain as well as Grays and Harvey valleys. The watershed boundary was used to determine the extent of this subregion. The Poison Lake subunit north of State Route 44 near Pittville Road adjacent to South Cabin Reservoir and Ebey Lake. The western boundary is near Halls Flat Road. The Badger Mountain subunit is located north of Badger Mountain and east of State Route 89 and South of Potato Butte. Little Bunch Grass Meadow is included in this unit. The Lost Creek subunit is located south of Cinder Butte and west of the Hat Creek Rim. Lost Creek near Wilcox Road is within this subunit. The Goose Valley subunit is located in Shasta County northwest of the intersection of State Route 299 and Route 89 in Goose Valley north of Burney, California. The Long Valley subunit is located in Long Valley west of Black Ranch Road south of Long Valley Mountain and east of Lookout Mountain. The Cayton Creek subunit is located in Shasta County north of Cayton Valley and Lake Britton east of Route 89. The area includes the northwestern portion of the watershed boundary for Fort Mountain along Red Mountain Road. The subunit is located in the Shasta National Forest. The Timbered Crater subunit is located on the Shasta/Modoc/Siskiyou county border near Little Hot Springs Valley. The subunit includes the area adjacent to Timbered Crater up to the Whitehorse Mountains and Day Road. The Timbered Crater subunit includes an area which has been proposed to be designated by the BLM as a Research Natural Area for vernal pools.

Unit 2 A, B, and C, Stillwater Plains Unit, Shasta County (5,100 ha (12,601 ac))

This unit is proposed as critical habitat because it contains many occurrences of slender Orcutt grass (CNDDB 2001) living within large vernal pool grassland areas that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units (EPA 1994, Holland 1998, Shasta County 2001).

This area is comprised of old alluvial terraces above the Sacramento River associated with Igo, Tuscan, Moda, and Redding soils (CNDDB 2001), which provide vernal pool habitat for the species. These pool types provide the necessary timing and duration of inundation necessary for slender Orcutt grass growth, germination, and reproduction. This unit represents the northern extent of the species range in the Sacramento Valley. The majority of the lands included within this unit are privately owned. Urban expansion from the city of Redding has greatly affected existing vernal pool habitats throughout this unit.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass germination and reproduction. The BLM owns 33 ha (81 ac) in the unit, while the NRCS holds conservation easements or agreements on an additional 52 ha (130 ac) through its WRP program.

The Stillwater Plains Unit 2 contains three subunits. These are located in the area east and south of the city of Redding near the Redding Municipal Airport encompassing Stillwater Plains to the confluence of the Sacramento River and Cow Creek. This unit is also part of vernal pool fairy shrimp Unit 5 and vernal pool tadpole shrimp Unit 1. Other sensitive species occurring within this unit include Red Bluff dwarf rush, California linderiella, and Henderson's bent grass.

Unit 3, Inskip Hill, Tehama and Shasta Counties (20,446 ha (50,522 ac))

This unit is proposed as critical habitat for slender Orcutt grass because it supports occurrences of the species within vernal pools on Guenon, Inskip, Inks, and Toomes soils (CNDDB 2002). The vernal pool habitats remain inundated for sufficient periods of time to allow the species to germinate, grow, and produce seed. The area supports over 40 percent of the known occurrences the species (CNDDB 2002) and is important in maintaining a diversity of habitats for slender Orcutt grass. This unit contains large vernal pool complexes that represent some of the last remaining lower elevation vernal pool habitats in the northern Sacramento Valley. These habitats are important to maintain the geographical distribution of slender Orcutt grass in the area.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass germination and reproduction.

Land ownership within this unit includes BLM (6,226 (15,384 ac)), CDFG (52 ha (130 ac)), State Land Commission (380 ha (950 ac)). The CDFG administers approximately 17 ha (42 ac) and the TNC has conservation easements on 6,230 (15,575 ac) within this unit. The remaining lands included within this unit are privately owned and urban development east of Redding threatens the vernal pool habitats within this area. This unit occupies the area south of the Tehama/Shasta county line south to Sevenmile Creek near the Tuscan Buttes. The eastern boundary encompasses the vernal pool habitats along the lower elevation bordering the Sacramento River. The western boundary roughly follows the Sacramento River. Table Mountain west of the Sacramento River north of Paynes Creek and Red Bluff is included in this unit. This unit coincides within Unit 2 for vernal pool tadpole shrimp.

Unit 4, Vina Plains Unit, Tehama and Butte Counties (11,673 ha (28,845 ac))

This unit is proposed as critical habitat for slender Orcutt grass because it supports occurrences of the species within vernal pools on Tuscan loam and Inks soils (CNDDB 2002) and the vernal pool habitats provide the necessary timing and length of inundation for slender Orcutt grass germination, growth, and reproduction. This area is over 160 km (100 mi) from the nearest area occupied by slender Orcutt grass to the south.

The boundaries of this unit were delineated by using SPOT imagery and elevation contours to include the open flat area associated with the vernal pool including the adjacent uplands that contribute to the filling and drying of the vernal pools where slender Orcutt grass occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass to germinate and reproduce.

The majority of the lands included within this unit are privately owned. This unit contains TNC's 1862 ha (4,600 ac) Vina Plains preserve. The preserve contains over 300 species of plants, and diverse communities of aquatic invertebrates. Since the 1960s, the Vina Plains area has been the focus of a number of research projects, including long-term adaptive management and monitoring efforts evaluating of the effects of grazing and fire on vernal pool plants (Griggs 2000). Much of the basic life history information known about slender Orcutt grass was collected at Vina Plains (e.g., Stone et al. 1988, Alexander and Schlising 1997). The results of this research have provided crucial information to guide management and monitoring of vernal pool ecosystems and to identify factors which influence population dynamics of a number of endangered species, including slender Orcutt grass. In addition to TNC, the importance of vernal pool habitats in this area has been recognized by the CDFG, the Service, the EPA, the CNPS, the NRCS's WRP, and by researchers at the CSU at Chico, who have all supported research and conservation efforts for slender Orcutt grass and other vernal pool species within this unit. Property ownership and protection within this unit includes CDFG (0.4 ha (1 ac)), CDFG administered land (0.4 ha (1 ac)), TNC (77 ha (192 ac)), TNC easements (4,661 ha (11,653)), and private land under WRP easements or agreements (57 ha, 142 ac)).

This unit for slender Orcutt grass occupies the area south of Toomes Creek, and north of Pine Creek and the Cana Highway. State Route 99 bisects this unit and the western boundary generally parallels the Southern Pacific Railway line. This unit is within Unit 7 for vernal pool fairy shrimp and Unit 3 for vernal pool tadpole shrimp, and includes part of Unit 1 for Conservancy fairy shrimp and Unit 1 for Hoover's spurge. The unit coincides with Unit 1 for hairy Orcutt grass and Unit 2 for Greene's tuctoria. Additional sensitive vernal pool species occurring in this unit include California linderiella, and Bogg's Lake hedge-hyssop.

Unit 5A and B, Bogg's Lake Unit, Clear Lake Area, Lake County (1,696 ha (4,191 ac))

This unit is proposed as critical habitat for slender Orcutt grass because it supports occurrences of the species within Northern Volcanic Ashflow vernal pools (Keeler-Wolf et al. 1998, CNDDB 2002). This area represents the western extent of the slender Orcutt grass's range, and some of the last remaining vernal pool habitats in Lake County. This unit is over 135 km (84 mi) from the nearest units to the north and west. Isolated and peripheral populations such as this may have genetic characteristics essential to the overall long-term conservation of the species (i.e., they may be different from other populations in other parts of its range) (Lesica and Allendorf 1995). This is the only unit which contains examples of Northern Volcanic Ash Flow vernal pools and has occurrences of slender Orcutt grass.

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass germination and reproduction.

The majority of lands within this unit are privately owned. TNC has protected the area around Bogg's Lake south of Clear Lake, but most of the area is not protected. Property ownership and protection within this unit includes CDFG (5 ha (13 ac)) and TNC (77 ha (192 ac)) lands. Threats to these subunits include conversion of rangeland to vineyards, overgrazing, erosion, draining, and urban expansion.

This unit consists of two subunits that are both located south of Clear Lake. The southernmost subunit includes Little High Valley. Other sensitive species found within this unit include Loch Lomond button-celery (Eryngium constancei), Burke's goldfields (Lasthenia burkei), Bogg's Lake hedge-hyssop, many-flowered navarretia (Navarretia leucocephala ssp. plieantha), few-flowered navarretia, and legenere.

Unit 6, Southeast Sacramento Valley Unit, Rancho Cordova, Sacramento County (8,853 ha (21,875 ac))

This unit is proposed as critical habitat for slender Orcutt grass because it supports occurrences of the species within vernal pools on Redding soils and is the southern extent of the species range (CNDDB 2001, Holland 1998). This unit is over 170 km (105 mi) from the nearest units to the north, and 100 km (62 mi) from the nearest unit to the west. Isolated and peripheral populations such as this may have genetic characteristics essential to the overall long-term conservation of the species (i.e., they may be different from more central populations) (Lesica and Allendorf 1995).

The boundaries of this unit were delineated to include the interconnected pools, swales, and associated uplands mapped by Holland (1998) that contribute to the filling and drying of the vernal pools where the species occur, and to maintain suitable periods of pool inundation, water quality, and soil moisture for slender Orcutt grass germination and reproduction.

This unit occupies the area southeast of Mather Field of Laguna Creek and north of the Sacramento and San Joaquin county line along Dry Creek. The eastern boundary is near Scott Road. The western limit is bounded by urban and agricultural areas near the cities of Galt and Elk Grove. This unit also is included in Unit 8 for vernal pool tadpole shrimp and Unit 13 for vernal pool fairy shrimp and coincides with Unit 2 for Sacramento Orcutt grass. Other sensitive vernal pool species located within this unit include California linderiella, legenere, Bogg's Lake hedge-hyssop, Ahart's dwarf rush, and western spadefoot toad. All the lands within this unit are privately owned.

Solano Grass Criteria

In proposing critical habitat units for Solano Grass we evaluated the life history and current distribution of the species, the primary constituent elements, and the current threats to the species. This information allowed us to determine which areas are likely to contribute to the conservation Solano grass.

Solano grass is only known from two locations, Jepson Prairie in Solano County, (consisting of two CNDDB occurrences, including the type locality) and the Davis Communications Annex in Yolo County. Solano grass is presumed to remain extant at the type locality, although only four individual plants have been found within the last decade, all in 1993 (CNDDB 2001). The decline of this species at Olcott Lake is attributed to two primary causes—hydrological alterations (Griggs in litt. 2000) and over collection (K. Fuller USFWS pers. comm.1998). Competition, livestock grazing, and off-road vehicle activity may have contributed to its decline (Service 1985c, Witham in litt. 1992, CNDDB 2001). The hydrology has been affected by the nearby road, Cook Lane, which functions like a dam to hold water in the lake, artificially increasing the water level and duration of inundation (Griggs in litt. 2000). The Yolo County habitat has been damaged by application of herbicides and salt (Witham in litt. 2000a). An undetermined number of Solano grass occurrences are presumed to have been extirpated by agricultural conversion before they were documented (Service 1985c, CDFG 1991).

Competition from aggressive plants poses a potential threat to Solano grass at all three known sites. The primary competitors are lippia at Olcott Lake (Witham in litt. 2000a), alkali mallow and swamp grass at the other site in Solano County (CNDDB 2001), and broad-leaved pepper-weed (Lepidium latifolium) in Yolo County (K. Fuller 2002 pers. comm.). Grazing apparently is detrimental to Solano grass but likely depends on the number and type of livestock and the season of use. Exclusion of horses from the Olcott Lake site was followed by an increase in population size (Service 1985c). At last report, sheep still grazed the other Solano County population (CNDDB 2001).

A number of factors threaten the Yolo County population in addition to competition, including herbicide runoff and soil disturbance from the creation and maintenance of fire breaks and borrow pits (CNDDB 2001, Witham in litt. 2000a). The site is not protected but does occur on DOD land.

Solano Grass Unit Review

We conducted a regional review across the range of Solano grass to evaluate and select areas that are essential to the conservation of the species and that may require special management. Important factors we considered were the known presence of the species and the presence of the primary constituent elements essential to the conservation of the species. A specific description of each area is outlined below.

Unit 1, Davis Communications Annex and Grasslands Area Unit, Yolo County (192 ha (474 ac))

This unit is proposed as critical habitat for Solano grass because it supports the largest extant occurrence of the species within Northern Claypan vernal pools on Pescadero soils (CNDDB 2002). The unit boundary was drawn to include the vernal pool complex mapped by Holland (1998) and Yolo County Parks (2001) where Solano grass is known to occur. This vernal pool complex maintains suitable periods of pool inundation, water quality, and soil moisture for Solano grass germination, growth and reproduction, and dispersal, but not necessarily every year. This unit represents the northern extent of the range of Solano grass, and is one of only two areas where the species is known to occur. Solano grass in this unit is threatened by altered hydrology, contamination, competition with invasive plant species, and surface disturbances such as discing. This unit is designated to encourage that special management actions be taken, such as grazing, fencing, and the implementation of a targeted management and monitoring plan be implemented to prevent the decline of Solano grass at this location (Yolo County Parks 2001).

This unit is located southeast of the City of Davis and south of the South Fork of Putah Creek. This unit's western boundary lies along the border between Solano and Yolo counties. This unit represents Unit 2 for Colusa grass and Unit 10 for vernal pool tadpole shrimp. Other rare vernal pool species found in this unit include alkali milk-vetch. This area is currently being addressed by local conservation planning efforts and contains land owned by Yolo County and the DOD (130 ha (321 ac)).

Unit 2, Jepson Prairie Unit, Solano County (7,153 ha (17,675 ac))

This unit is designated as critical habitat for Solano grass because it supports occurrences of the species within large playa vernal pools on the Pescadero soil series which provide habitat for Solano grass (USDA 2001, Holland 1998, Solano County Water Agency 2000, Solano County Farmlands and Open Space 2000, CNDDB 2002). This area represents the largest contiguous area of habitat remaining for the species, and contains two of the three known occurrences of Solano grass, although one of these occurrences has not been observed since 1993. Vernal pool habitats within the greater Jepson Prairie grassland area that are not likely to support Solano grass occurrences were not included within this unit. This unit represents the southern extent of Solano grass range.

The Jepson Prairie Unit for Solano grass is a portion of the greater Jepson Prairie grassland area, one of the most pristine, intact vernal pool ecosystems remaining in the State of California. Jepson Prairie contains large, playa-like vernal pools which may be over several acres in size, including the 32 ha (80 ac) Olcott Lake. These larger pools often occur in complexes with smaller pools and hogwallow depressions. This unit includes the Jepson Prairie Preserve, jointly managed by the Solano County Farmlands and Open Space Foundation and the UC Reserve System. Jepson Prairie is the target of ongoing conservation planning and active management. As part of the UC Reserve System, this area also provides critical research opportunities for scientists to study vernal pool species, including Solano grass. Solano grass has experienced unexplained declines at Olcott Lake in Jepson Prairie, and research investigating the cause of this decline is essential to ensure the recovery of Solano grass. The unit also contains Ecological Reserves totaling 248 ha (620 ac) owned and approximately 64 ha (161 ac) administered by CDFG. Additional lands are owned by the Travis Air Force Base (93 ha (233 ac)), and the State Land Commission (7 ha (17 ac)). NRCS also holds conservation easements or agreements on 436 ha (1,090 ac) of private land in the unit through the WRP program. Within the greater Jepson Prairie grassland area, existing vernal pools are threatened by agricultural conversion, landfill expansion, power plant construction, and utility maintenance.

This unit is situated east of the City of Fairfield, south of the City of Dixon, and north of the Montezuma Hills and the confluence of the Sacramento and San Joaquin rivers. This unit coincides with Unit 2 for Colusa grass. This unit is encompassed by Unit 3 for Conservancy fairy shrimp, Unit 11 for vernal pool tadpole shrimp and Unit 16 for vernal pool fairy shrimp. This unit also supports a diverse community of plants and animals, including the only known occurrence of delta green ground beetle, and occurrences of California tiger salamander, alkali milk-vetch, Bogg's Lake hedge-hyssop, legenere, California linderiella, and midvalley fairy shrimp.

Additional Considerations

In defining critical habitat boundaries, we made an effort to avoid developed areas, such as towns and other similarly developed lands, and intensively farmed lands that are unlikely to contribute to conservation of the species. However, the resolution of the SPOT imagery and the vernal pool and species occurrence information we used did not allow us to identify these areas at a sufficiently fine scale to exclude all developed areas, such as towns, housing developments, or other lands unlikely to contain the primary constituent elements. Existing features and structures within the boundaries of the mapped units, such as buildings, roads, aqueducts, railroads, airport runways, other paved areas, lawns, landscaped areas, and most intensively farmed areas, and other urban areas, will not contain one or more of the primary constituent elements. Federal actions limited to those areas, therefore, would not trigger section 7 consultation, unless they affect the species and/or primary constituent elements in adjacent critical habitat.

Effects of Critical Habitat Designation

Section 7 Consultation

Section 7(a) of the Act requires Federal agencies, including the Service, to ensure that actions they fund, authorize, permit, or carry out do not destroy or adversely modify critical habitat. Destruction or adverse modification of critical habitat occurs when a Federal action directly or indirectly alters critical habitat to the extent it appreciably diminishes the value of critical habitat for the conservation of the species. Individuals, organizations, States, local governments, and other non-Federal entities are affected by the designation of critical habitat only if their actions occur on Federal lands, require a Federal permit, license, or other authorization, or involve Federal funding.

Section 7(a) of the Act requires Federal agencies, including the Service, to evaluate their actions with respect to any species that is proposed or listed as endangered or threatened, and with respect to its critical habitat, if any is designated or proposed. Regulations implementing this interagency cooperation provision of the Act are codified at 50 CFR part 402. Section 7(a)(4) of the Act requires Federal agencies to confer with us on any action that is likely to jeopardize the continued existence of a species proposed for listing, or result in destruction or adverse modification of proposed critical habitat. Conference reports provide conservation recommendations to assist the action agency in eliminating conflicts that may be caused by the proposed action. The conservation measures in a conference report are advisory.

We may issue a formal conference report, if requested by the Federal action agency. Formal conference reports include an opinion that is prepared according to 50 CFR 402.14, as if the species was listed or critical habitat designated. We may adopt the formal conference report as the biological opinion when the species is listed or critical habitat designated, if no substantial new information or changes in the action alter the content of the opinion (50 CFR 402.10(d)).

If a species is listed or critical habitat is designated, section 7(a)(2) of the Act requires Federal agencies to ensure that activities they authorize, fund, or carry out are not likely to jeopardize the continued existence of such a species or to destroy or adversely modify its critical habitat. If a Federal action may affect a listed species or its critical habitat, the responsible Federal agency (action agency) must enter into consultation with us. Through this consultation, the Federal action agency would ensure that the permitted actions do not destroy or adversely modify critical habitat.

If we issue a biological opinion concluding that a project is likely to result in the destruction or adverse modification of critical habitat, we also provide “reasonable and prudent alternatives” to the project, if any are identifiable. Reasonable and prudent alternatives are defined at 50 CFR 402.02 as alternative actions identified during consultation that can be implemented in a manner consistent with the intended purpose of the action, that are consistent with the scope of the Federal agency's legal authority and jurisdiction, that are economically and technologically feasible, and that the Director believes would avoid the likelihood of jeopardizing the continued existence of listed species, or resulting in the destruction or adverse modification of critical habitat. Reasonable and prudent alternatives can vary from slight project modification to extensive redesign or relocation of the project.

Regulations at 50 CFR 402.16 require Federal agencies to reinitiate consultation on previously reviewed actions under certain circumstances, including instances where critical habitat is subsequently designated and the Federal agency has retained discretionary involvement, or control has been retained, or is authorized by law. Consequently, some Federal agencies may request reinitiation of consultation or conference with us on actions for which formal consultations have been completed, if those actions may affect designated critical habitat or adversely modify or destroy proposed critical habitat.

Activities on Federal lands that may jeopardize vernal pool crustaceans or vernal pool plants or adversely modify their critical habitat will require section 7 consultation. Activities on private lands that require a permit from a Federal agency, such as a permit from the Corps under section 404 of the Clean Water Act (33 U.S.C. 1344 et seq.), a section 10(a)(1)(B) of the Act permit from the Service, or any other activity requiring Federal action (i.e., funding or authorization from the Federal Highways Administration or Federal Emergency Management Agency) will also continue to be subject to the section 7 consultation process. Federal actions not affecting listed species or critical habitat, and actions on non-Federal lands that are not federally funded, authorized, or permitted do not require section 7 consultation. Not all of the areas within these units are capable of supporting vernal pool crustaceans or vernal pool plants or their primary constituent elements, and such areas would not be subject to section 7 consultation.

To properly portray the effects of critical habitat designation, we must first compare the section 7 requirements for actions that may affect critical habitat with the requirements for actions that may affect a listed species. Section 7 ensures that actions funded, authorized, or carried out by Federal agencies are not likely to jeopardize the continued existence of a listed species, or destroy or adversely modify the listed species' critical habitat. Actions likely to jeopardize the continued existence of a species are those that would appreciably reduce the likelihood of the species' survival and recovery. Actions likely to “destroy or adversely modify” critical habitat are those that would appreciably reduce the value of critical habitat for the survival and recovery of the listed species.

Common to both definitions is an appreciable detrimental effect on the recovery of a listed species. Given the similarity of these definitions, actions likely to destroy or adversely modify critical habitat would almost always result in jeopardy to the species concerned, particularly when the species is present in the area of the proposed action. When the species is present in an area, designation of critical habitat for vernal pool crustaceans or vernal pool plants is not likely to result in regulatory requirements above those already in place due to the presence of the listed species. When the species is not present in an area, designation of critical habitat for vernal pool crustaceans or vernal pool plants may result in an additional regulatory burden when a Federal nexus exists.

Section 4(b)(8) of the Act requires us to evaluate briefly and describe, in any proposed or final regulation that designates critical habitat, those activities involving a Federal action that may adversely modify such habitat or that may be affected by such designation. Activities that may destroy or adversely modify critical habitat would be those that alter the primary constituent elements to the extent that the value of critical habitat for the conservation of vernal pool crustaceans or vernal pool plants is appreciably reduced. We note that such activities may also jeopardize the continued existence of the species.

Activities that, when carried out, funded, or authorized by a Federal agency may directly or indirectly destroy or adversely modify critical habitat for vernal pool crustaceans or vernal pool plants include, but are not limited to—

(1) Any activity, including the regulation of activities by the Corps under section 404 of the Clean Water Act or activities carried out by or authorized by the EPA, that could alter the suitability of the watershed or water quality or quantity to support vernal pool crustaceans or vernal pool plants, or any activity that adversely affects the natural hydrologic function of the vernal pool system and/or ephemeral pond or depression;

(2) Road construction and maintenance, right-of-way designation, and regulation of agricultural activities, or any activity funded or carried out by the Department of Transportation or Department of Agriculture that results in discharge of dredged or fill material, excavation, or mechanized land clearing of ephemeral and/or vernal pool basins;

(3) Sale or exchange of lands by a Federal agency to a non-Federal entity which could foreseeably impact the primary constituent elements of critical habitat;

(4) Regulation, relicensing, and operation of damming or other water impoundments by the BOR, Corps, or Federal Energy Regulatory Commission (FERC) that inundate critical habitat for vernal pool crustaceans;

(5) Regulation by the Federal Aviation Administration (FAA) of airport improvement or maintenance activities that could foreseeably impact the primary constituent elements of critical habitat;

(6) Licensing of construction of communication sites by the Federal Communications Commission (FCC) on lands containing critical habitat;

(7) Funding of construction or development activities by the Department of Housing and Urban Development (HUD) or other agencies that destroy, fragment, or degrade suitable critical habitat;

(8) Military training and maneuvers on applicable DOD lands which could foreseeably impact the primary constituent elements of critical habitat;

(9) Signing of contracts to deliver water by the BOR in situations where those deliveries could foreseeably impact the primary constituent elements of critical habitat; and

(10) Promulgation of a land use plan by a Federal agency such as the BLM, USFS, or DOD that may alter management practices for critical habitat.

If you have questions regarding whether specific activities will constitute adverse modification of critical habitat in California, contact the Field Supervisor, Sacramento Fish and Wildlife Office (see ADDRESSES section). If the critical habitat occurs in Oregon, contact the Field Supervisor, Oregon Fish and Wildlife Office, 2600 S.E. 98th Avenue, Portland, OR 97266. Requests for copies of the regulations on listed wildlife, and inquiries about prohibitions and permits may be addressed to the U.S. Fish and Wildlife Service, Branch of Endangered Species, 911 N.E. 11th Ave, Portland, OR 97232 (telephone 503/231-2063; facsimile 503/231-6243).

Section 3(5)(A) Special Management Considerations

Section 3(5)(A) of the Act defines critical habitat to be (among other things) areas within the current range of the species “which may require special management considerations”. Accordingly, areas which will not require such special considerations are not critical habitat. For areas in the current range of the species, we first determine whether the area contains the physical and biological features essential to the conservation of the species and then determine whether the area has or needs special management or protection. Additional special management is not required if adequate management or protection is already in place. Adequate special management or protection is provided by a legally operative plan or agreement that addresses the maintenance and improvement of the primary constituent elements important to the species, and manages for the long-term conservation of the species. We use the following three criteria to determine if a plan provides adequate special management or protection: (1) A current plan or agreement must be complete and provide sufficient conservation benefit to the species, (2) the plan or agreement must provide assurances that the conservation management strategies will be implemented, and (3) the plan or agreement must provide assurances that the conservation management strategies will be effective, i.e., provide for periodic monitoring and revisions as necessary. If all of these criteria are met, then the lands covered under the plan would no longer meet the definition of critical habitat.

The Sikes Act Improvements Act of 1997 (Sikes Act) requires each military installation that includes land and water suitable for the conservation and management of natural resources to complete, by November 17, 2001, an Integrated Natural Resources Management Plan (INRMP). An INRMP integrates implementation of the military mission of the installation with stewardship of the natural resources found there. Each INRMP includes an assessment of the ecological needs on the installation, including needs to provide for the conservation of listed species; a statement of goals and priorities; a detailed description of management actions to be implemented to provide for these ecological needs; and a monitoring and adaptive management plan. We consult with the military on the development and implementation of INRMPs for installations with listed species. We believe military bases that have completed and approved INRMPs that address the needs of the species generally do not meet the definition of critical habitat discussed above, as they require no additional special management or protection.

We evaluated the status of INRMPs on DOD lands that were within the proposed critical habitat to determine whether any INRMPs met the special management criteria. To date, no DOD installation has completed a final INRMP that provides for sufficient conservation management and protection for the vernal pool crustaceans and plants. All DOD lands that contain the physical and biological features essential for the conservation of one of the vernal pool species have been included in the proposed designation of critical habitat for that species. Although no INRMPs for the vernal pool crustaceans and plants are currently in place on DOD lands within the proposed critical habitat, we will continue to work with the military bases to develop INRMPs to meet the special management criteria to preclude the final designation of critical habitat on their lands.

Exclusions Under Section 4(b)(2)

Subsection 4(b)(2) of the Act allows us to exclude from critical habitat designation areas where the benefits of exclusion outweigh the benefits of designation, provided the exclusion will not result in the extinction of the species. However, prior to excluding these areas from critical habitat, we believe that it is best to fully and specifically describe the areas in the proposed designation, discuss our intent and rationale as to why we believe the areas should be excluded from designated critical habitat, and solicit public comment on the exclusion of these areas.

We believe the proposed Skunk Hollow critical habitat (Unit 35) in Riverside County may warrant exclusion from the final designation of critical habitat under section 4(b)(2) of the Act based on the special management considerations and protections afforded the vernal pool habitat through several approved and legally operative HCPs. We believe that in most instances the benefits of excluding legally operative HCPs from the critical habitat designations will outweigh the benefits of including them. The following represents our rationale for proposing to exclude the Skunk Hollow critical habitat unit (Unit 35) from the final designated critical habitat.

(1) Benefits of Exclusion

The benefits of excluding HCPs include relieving landowners, communities and counties of any additional regulatory burden that might be imposed by critical habitat. This benefit is particularly compelling given the past representations on the part of the Service that once an HCP is negotiated and approved by us after public comment, activities consistent with the plan will satisfy the requirements of the Endangered Species Act. Many HCPs, particularly large regional HCPs, take many years to develop and, upon completion, become regional conservation plans that are consistent with the recovery of covered species. Imposing an additional regulatory review after HCP completion may jeopardize conservation efforts and partnerships in many areas and could be viewed as a disincentive to those developing HCPs. Excluding HCPs provides the Service an opportunity to streamline regulatory compliance, and provides regulatory certainty for HCP participants.

Another critical benefit of excluding HCPs is that it would encourage the continued development of partnerships with HCP participants, including states, local governments, conservation organizations, and private landowners, that together can implement conservation actions we would be unable to accomplish. By excluding areas covered by HCPs from critical habitat designation, we clearly maintain our commitments, preserve these partnerships, and, we believe, set the stage for more effective conservation actions in the future.

(2) Benefits of Inclusion

The benefits of including HCPs in critical habitat are normally small. The principal benefit of any designated critical habitat is that activities in such habitat that may affect it require consultation under section 7 of the Act. Such consultation would ensure that adequate protection is provided to avoid adverse modification of critical habitat. Where HCPs are in place, our experience indicates that this benefit is small or non-existent. Currently approved and permitted HCPs are already designed to ensure the long-term survival of covered species within the plan area. Where we have an approved HCP, lands that we ordinarily would define as critical habitat for covered species will normally be protected in reserves and other conservation lands by the terms of the HCPs and their Implementing Agreements. These HCPs and Implementing Agreements include management measures and protections for conservation lands designed to protect, restore, and enhance their value as habitat for covered species.

In addition, an HCP application must itself be consulted upon. While this consultation will not look specifically at the issue of adverse modification of critical habitat, unless critical habitat has already been designated within the proposed plan area, it will look at the very similar concept of jeopardy to the listed species in the plan area. Because HCPs, particularly large regional HCPs, address land use within the plan boundaries, habitat issues within the plan boundaries will have been thoroughly addressed in the HCP and through the consultation on the HCP. Our experience is also that, under most circumstances, consultations under the jeopardy standard will reach the same result as consultations under the adverse modification standard. Implementing regulations (50 CFR 402.02 ) define “jeopardize the continued existence of” and “destruction or adverse modification of” in virtually identical terms. “Jeopardize the continued existence of” means to engage in an action “that reasonably would be expected, directly or indirectly, to reduce appreciably the likelihood of both the survival and recovery of a listed species.” Destruction or adverse modification means an “alteration that appreciably diminishes the value of critical habitat for both the survival and recovery of a listed species.” Common to both definitions is an appreciable detrimental effect on both survival and recovery of a listed species, in the case of critical habitat, by reducing the value of the habitat so designated. Thus, actions satisfying the standard for adverse modification are nearly always found to also jeopardize the species concerned, and the existence of a critical habitat designation does not materially affect the outcome of consultation. Additional measures to protect the habitat from adverse modification are not likely to be required.

Further, HCPs typically provide for greater conservation benefits to a covered species than section 7 consultations because HCPs assure the long-term protection and management of a covered species and its habitat, and funding for such management through the standards found in the 5 Point Policy for HCPs (64 FR 35242) and the HCP No Surprises regulation (63 FR 8859). Such assurances are typically not provided by section 7 consultations which, in contrast to HCPs, often do not commit the project proponent to long-term special management or protections. Thus, a consultation typically does not accord the lands it covers the extensive benefits an HCP provides. The development and implementation of HCPs provide other important conservation benefits, including the development of biological information to guide conservation efforts and assist in species recovery, and the creation of innovative solutions to conserve species while allowing for development. The education benefits of critical habitat, including informing the public of areas that are important for long-term survival and conservation of the species, are essentially the same as those that would occur from the public notice and comment procedures required to establish an HCP, as well as the public participation that occurs in the development of many regional HCPs. For these reasons, then, we believe, that designation of critical habitat has little benefit in areas covered by HCPs, provided that the HCP and its associated Implementing Agreement are legally operative, and that the HCP specifically and adequately covers the species for which critical habitat is being designated.

We have reviewed and evaluated HCPs currently approved and being properly and legally implemented within the areas being proposed for critical habitat for the vernal pool crustaceans and plants. Based on this evaluation, we find that the benefits of exclusion outweigh the benefits of designating the Skunk Hollow vernal pool (Unit 35) as critical habitat. The Skunk Hollow vernal pool basin consists of a single, large vernal pool and its essential associated watershed in western Riverside County. Several federally listed species have been documented from the Skunk Hollow vernal pool basin. These include the threatened vernal pool fairy shrimp (Simovich in litt 2001), the endangered Riverside fairy shrimp (Streptocephalus woottoni) (Service 2001), the threatened spreading navarretia (Navarretia fossalis), and the endangered California Orcutt grass (Orcuttia californica) (Service 1998). The vernal pool complex and watershed is currently protected as part of a reserve established within an approved mitigation bank in the Rancho Bella Vista HCP area and as part of the conservation measures contained in the Assessment District 161 Subregional HCP. While neither HCP include vernal pool fairy shrimp as a covered species, both HCPs provide protection for the vernal pool complex and its associated watershed in perpetuity. Further, the HCPs address the endangered Riverside fairy shrimp as a covered species. We believe that the management and protections afforded the vernal pool complex and the Riverside fairy shrimp are adequate for the long-term conservation of this complex and this species, and to preserve the partnerships that we have developed with the local jurisdiction and project proponents in the development of these HCPs, we excluded the Skunk Hollow vernal pool complex from critical habitat for the Riverside fairy shrimp. We did not and still do not believe that this exclusion from critical habitat will result in the extinction of this Riverside fairy shrimp.

Even though the two HCPs do not have vernal pool fairy shrimp listed as a covered species, we believe that the protections and management afforded the Skunk Hollow vernal pool complex and the other listed vernal pool species through the terms and conditions of those HCPs are adequate to ensure the long-term conservation of vernal pool fairy shrimp as well. Therefore, as with the Riverside fairy shrimp, we believe that the benefits of the exclusion of the Skunk Hollow vernal pool complex from critical habitat for vernal pool fairy shrimp outweighs the benefit of its inclusion. Additionally, we do not believe that this exclusion would result in the extinction of vernal pool fairy shrimp.

Several HCP efforts are now under way that will address the conservation needs of the vernal pool crustaceans and plants in areas we propose as critical habitat. We have worked and continue to work closely with the HCP proponents to adequately address the conservation needs of these species within the boundaries of the HCPs. In the event that future HCPs, covering any of the vernal pool crustaceans or plants are developed within the boundaries of designated critical habitat, we will work with applicants to ensure that the HCPs provide for protection and management of habitat areas essential for the conservation of those species by either directing development and habitat modification to nonessential areas or appropriately modifying activities within essential habitat areas so that such activities will not destroy or adversely modify the primary constituent elements. The HCP development process provides an opportunity for more intensive data collection and analysis regarding the use of particular habitat areas by vernal pool crustaceans and plants. The process also enables us to conduct detailed evaluations of the importance of such lands to the long-term survival of these species in the context of constructing a biologically configured system of interlinked habitat blocks. We fully expect that HCPs undertaken by local jurisdictions (e.g., counties, cities) and other parties will identify, protect, and provide appropriate management for those specific lands within the boundaries of the plans that are essential for the long-term conservation of the species. We believe and fully expect that our analyses of these proposed HCPs and proposed permits under section 7 of the Act will show that covered activities carried out in accordance with the provisions of the HCPs and biological opinions will not result in destruction or adverse modification of critical habitat. We will provide technical assistance and work closely with applicants with respect to HCPs currently under development and future HCPs to identify lands essential for the long-term conservation of the vernal pool crustaceans and plants and appropriate management for those lands. The minimization and mitigation measures provided under these HCPs are expected to protect the essential habitat lands proposed as critical habitat in this rule. If an HCP that addresses any vernal pool crustacean or plant as a covered species is ultimately approved, we will reassess the critical habitat boundaries in light of the HCP. We intend to undertake this review when the HCP is approved, but funding and priority constraints may influence the timing of such a review. Should additional information become available that changes our analysis of the benefits of excluding any of these (or other) areas compared to the benefits of including them in the critical habitat designation, we may revise this proposed designation accordingly. Similarly, if new information indicates any areas we are proposing now should not be included in the critical habitat designation because they no longer meet the definition of critical habitat, we may revise this proposed critical habitat designation.

Economic Analysis

Section 4(b)(2) of the Act requires us to designate critical habitat on the basis of the best scientific and commercial data available, and to consider the economic and other relevant impacts of designating a particular area as critical habitat. We may exclude areas from critical habitat upon a determination that the benefits of such exclusions outweigh the benefits of specifying such areas as critical habitat. We cannot exclude such areas from critical habitat when such exclusion will result in the extinction of the species. We will conduct an analysis of the economic impacts of designating these areas as critical habitat prior to a final determination. When completed, we will announce the availability of the draft economic analysis with a notice in the Federal Register, and we will open a public comment period on the draft economic analysis and re-open the comment period on the proposed rule at that time.

Public Comments Solicited

We intend that any final action resulting from this proposal will be as accurate and effective as possible. Therefore, we solicit comments or suggestions from the public, other concerned governmental agencies, the scientific community, industry, or any other interested party concerning this proposed rule. We particularly seek comments concerning:

(1) The reasons why any habitat should or should not be determined to be critical habitat as provided by section 4 of the Act, including whether the benefits of designation will outweigh any threats to the species due to designation and whether areas under consideration require additional special management;

(2) Specific information on the amount and distribution of any of the vernal pool crustaceans or vernal pool plants and what habitat is essential to the conservation of these species and why;

(3) Land use designations and current or planned activities in the subject areas and their possible impacts on proposed critical habitat; in particular, in Oregon, we seek information related to potential of selected parcels to contribute to the species recovery, considering their zoning, adjacent land uses, watershed integrity, and potential for edge effects (related to shape of parcel);

(4) Any foreseeable economic or other impacts resulting from the proposed designation of critical habitat, in particular, any impacts on small entities or families;

(5) Economic and other values associated with designating critical habitat for vernal pool crustaceans and vernal pool plants such as those derived from non-consumptive uses (e.g., hiking, camping, bird-watching, enhanced watershed protection, improved air quality, increased soil retention, “existence values,” and reductions in administrative costs);

(6) Whether any areas should be excluded pursuant to section 4(b)(2); and

(7) Whether our approach to critical habitat designation could be improved or modified in any way to provide for greater public participation and understanding, or to assist us in accommodating public concern and comments.

If you wish to comment on this proposed rule, you may submit your comments and materials by any one of several methods (see ADDRESSES). Please submit electronic mail comments as an ASCII file and avoid the use of special characters and any form of encryption. Please also include “Attn: [RIN number]” and your name and return address in your electronic message. Please note that the electronic address fw1_vernalpool@fws.gov will be closed out at the termination of the public comment period. If you do not receive a confirmation from the system that we have received your electronic message, contact us directly by calling our Sacramento Fish and Wildlife Office at phone number 916/414-6600.

Our practice is to make comments, including names and home addresses of respondents, available for public review during regular business hours. Individual respondents may request that we withhold their home address from the rulemaking record, which we will honor to the extent allowable by law. In some circumstances, we would withhold from the rulemaking record a respondent's identity, as allowable by law. If you wish us to withhold your name and/or address, you must state this prominently at the beginning of your comment. However, we will not consider anonymous comments. To the extent consistent with applicable law, we will make all submissions from organizations or businesses, and from individuals identifying themselves as representatives or officials of organizations or businesses, available for public inspection in their entirety. Comments and materials received will be made available for public inspection, by appointment, during normal business hours at the above address.

Peer Review

In accordance with our policy published on July 1, 1994 (59 FR 34270), we will solicit the expert opinions of at least three appropriate and independent specialists regarding this proposed rule. The purpose of such review is to ensure listing decisions are based on scientifically sound data, assumptions, and analyses. We will send these peer reviewers copies of this proposed rule immediately following publication in the Federal Register. We will invite these peer reviewers to comment, during the public comment period, on the specific assumptions and conclusions regarding the proposed designation of critical habitat.

We will consider all comments and information received during the 120-day public comment period on this proposed rule during preparation of a final rulemaking. Accordingly, the final decision may differ from this proposal.

Public Hearings

The Act provides for one or more public hearings on this proposal, if requested. Requests for public hearings must be made at least 15 days prior to the close of the public comment period. We will schedule public hearings on this proposal, if any are requested, and announce the dates, times, and places of those hearings in the Federal Register and local newspapers at least 15 days before the first hearing is held.

Clarity of the Rule

Executive Order 12866 requires each agency to write regulations and notices that are easy to understand. We invite your comments on how to make this proposed rule easier to understand, including answers to questions such as the following: (1) Are the requirements in the proposed rule clearly stated? (2) Does the proposed rule contain technical language or jargon that interferes with the clarity? (3) Does the format of the proposed rule (grouping and order of sections, use of headings, paragraphing, etc.) aid or reduce its clarity? (4) Is the description of the proposed rule in the SUPPLEMENTARY INFORMATION section of the preamble helpful in understanding the proposed rule? What else could we do to make the proposed rule easier to understand?

Send a copy of any comments that concern how we could make this rule easier to understand to: Office of Regulatory Affairs, Department of Interior, Room 7229, 1849 C Street, NW., Washington, DC 20240. You may e-mail your comments to this address: Exsec@ios.doi.gov.

Required Determinations

Regulatory Planning and Review

In accordance with Executive Order 12866, this document is a significant rule and was reviewed by the Office of Management and Budget (OMB). The Service is preparing a draft economic analysis of this proposed action. The Service will use this analysis to meet the requirement of section 4(b)(2) of the ESA to determine the economic consequences of designating the specific areas as critical habitat and excluding any area from critical habitat if it is determined that the benefits of such exclusion outweigh the benefits of specifying such areas as part of the critical habitat, unless failure to designate such area as critical habitat will lead to the extinction of any of the vernal pool species included in this rule. This analysis will be available for public comment before finalizing this designation. The availability of the draft economic analysis will be announced in the Federal Register.

Regulatory Flexibility Act (5 U.S.C. 601 et seq.)

This discussion is based upon the information regarding potential economic impact that is available to the Service at this time. This assessment of economic effect may be modified prior to final rulemaking based upon development and review of the economic analysis being prepared pursuant to section 4(b)(2) of the ESA and E.O. 12866. This analysis is for the purposes of compliance with the Regulatory Flexibility Act and does not reflect the position of the Service on the type of economic analysis required by New Mexico Cattle Growers Assn. v. U.S. Fish & Wildlife Service 248 F.3d 1277 (10th Cir. 2001).

Under the Regulatory Flexibility Act (5 U.S.C. 601 et seq., as amended by the Small Business Regulatory Enforcement Fairness Act (SBREFA) of 1996), whenever an agency is required to publish a notice of rulemaking for any proposed or final rule, it must prepare and make available for public comment a regulatory flexibility analysis that describes the effect of the rule on small entities (i.e., small businesses, small organizations, and small government jurisdictions). However, no regulatory flexibility analysis is required if the head of the agency certifies the rule will not have a significant economic impact on a substantial number of small entities. SBREFA amended the Regulatory Flexibility Act to require Federal agencies to provide a statement of the factual basis for certifying that a rule will not have a significant economic impact on a substantial number of small entities. SBREFA also amended the RFA to require a certification statement. We are hereby certifying that this proposed rule will not have a significant economic impact on a substantial number of small entities. The following discussion explains our rationale for making this assertion.

According to the Small Business Administration (http://www.sba.gov/size/),, small entities include small organizations, such as independent non-profit organizations, and small governmental jurisdictions, including school boards and city and town governments that serve fewer than 50,000 residents, as well as small businesses. Small businesses include manufacturing and mining concerns with fewer than 500 employees, wholesale trade entities with fewer than 100 employees, retail and service businesses with less than $5 million in annual sales, general and heavy construction businesses with less than $27.5 million in annual business, special trade contractors doing less than $11.5 million in annual business, and agricultural businesses with annual sales less than $750,000. To determine if potential economic impacts to these small entities are significant, we consider the types of activities that might trigger regulatory impacts under this rule as well as the types of project modifications that may result. In general, the term “significant economic impact” is meant to apply to a typical small business firm's business operations.

In determining whether this rule could “significantly affect a substantial number of small entities”, the economic analysis first determines whether critical habitat could potentially affect a “substantial number” of small entities in counties supporting critical habitat areas. While SBREFA does not explicitly define “substantial number,” the Small Business Administration, as well as other Federal agencies, have interpreted this to represent an impact on 20 percent or greater of the number of small entities in any industry. In some circumstances, especially with critical habitat designations of limited extent, we may aggregate across all industries and consider whether the total number of small entities affected is substantial. In estimating the numbers of small entities potentially affected, we also considered whether their activities have any Federal involvement. Designation of critical habitat only affects activities conducted, funded, or permitted by Federal agencies. Some kinds of activities are unlikely to have any Federal involvement and so will not be affected by critical habitat designation.

Designation of critical habitat only affects activities conducted, funded, or permitted by Federal agencies; non-Federal activities are not affected by the designation. In areas where the species are present, Federal agencies are already required to consult with us under section 7 of the Act on activities that they fund, permit, or implement that may affect vernal pool crustaceans and plants for whom designation of critical habitat is proposed. If this critical habitat designation is finalized, Federal agencies also must ensure, also through consultation with us, that their activities do not destroy or adversely modify designated critical habitat. However, for the reasons discussed above, we do not believe this will result in any additional regulatory burden on Federal agencies or their applicants.

In areas that we are proposing to designate as critical habitat where occupancy status is currently unknown, but is presumed to be likely, a potential does exist that designation as critical habitat would trigger additional Federal review for activities having a Federal nexus (e.g., funded, permitted, authorized, etc.). We base this determination upon the present and ongoing regulatory framework in which the Corps consults with us under section 7 of the Act in the vast majority of cases where their actions may affect vernal pools. These section 7 consultations are currently precipitated by either the known or presumed occupancy of one or more of the vernal pool crustaceans or plants addressed in this rule. In those rare circumstances where the Corps does not consult with us under section 7 of the Act, we believe that an HCP would still be required, based on known or a high likelihood of occupancy. Any change or deviation in the present regulatory climate is purely speculative at this time. Therefore, we do not expect the final designation of critical habitat as proposed in this rule to substantially increase the regulatory or economic burden on project proponents beyond that which is presently required through the likely presence of one or more listed species, where the necessary primary constituent elements are present. As a result of this minimal increase in the regulatory or economic burdens on any project proponents, we do not believe that this proposed designation of critical habitat for the vernal pool crustaceans and plants will cause a significant economic impact on a substantial number of small entities.

We note that for actions on non-Federal property that do not have a Federal connection (such as funding or authorization), the current restrictions concerning take of the species remain in effect, and that this proposed rule will place no additional restrictions on such activities.

Therefore, based on the above evaluation, we are certifying that this proposed designation of critical habitat for the vernal pool crustaceans and plants is not expected to have a significant economic impact on a substantial number of small entities, and that an initial regulatory flexibility analysis is not required. However, should the economic analysis of this proposed rule indicate that there may be significant economic impacts on a substantial number of small entities, we will revisit this determination.

Executive Order 13211

On May 18, 2001, the President issued an Executive Order (EO 13211) on regulations that significantly affect energy supply, distribution, and use. Executive Order 13211 requires agencies to prepare Statements of Energy Effects when undertaking certain actions. Although this rule is a significant regulatory action under Executive Order 12866, it is not expected to significantly affect energy supplies, distribution, or use. Therefore, this action is not a significant energy action and no Statement of Energy Effects is required.

Unfunded Mandates Reform Act (2 U.S.C. 1501 et seq.)

The Service will use the economic analysis to evaluate consistency with the Unfunded Mandates Reform Act (2 U.S.C. 1501 et seq.).

Takings

In accordance with Executive Order 12630 (“Government Actions and Interference with Constitutionally Protected Private Property Rights”), we have analyzed the potential takings implications of designating critical habitat for these 15 vernal pool species in a preliminary takings implications assessment. This preliminary assessment concludes that this proposed rule does not pose significant takings implications. However, we have not yet completed the economic analysis for this proposed rule. Once the economic analysis is available, we will review and revise this preliminary assessment as warranted.

Federalism

In accordance with Executive Order 13132, the rule does not have significant Federalism effects. A Federalism assessment is not required. In keeping with Department of the Interior policy, we requested information from, and coordinated development of this critical habitat proposal with appropriate State resource agencies in California. We will continue to coordinate any future designation of critical habitat for the vernal pool crustaceans and vernal pool plants with the appropriate State agencies. The designation of critical habitat in areas currently occupied by the vernal pool crustaceans and vernal pool plants imposes no additional restrictions to those currently in place and, therefore, has little incremental impact on State and local governments and their activities. The designation may have some benefit to these governments in that the areas essential to the conservation of the species are more clearly defined, and the primary constituent elements of the habitat necessary to the survival of the species are specifically identified. While making this definition and identification does not alter where and what federally sponsored activities may occur, it may assist these local governments in long range planning rather than waiting for case by case section 7 consultations to occur.

Civil Justice Reform

In accordance with Executive Order 12988, the Office of the Solicitor has determined that the rule does not unduly burden the judicial system and meets the requirements of sections 3(a) and 3(b)(2) of the Order. We designate critical habitat in accordance with the provisions of the Act. The rule uses standard property descriptions and identifies the primary constituent elements within the designated areas to assist the public in understanding the habitat needs of the vernal pool crustaceans or vernal pool plants.

Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.)

This rule does not contain any new collections of information that require approval by OMB under the Paperwork Reduction Act. This rule will not impose new record keeping or reporting requirements on State or local governments, individuals, businesses, or organizations. An agency may not conduct or sponsor, and a person is not required to respond to a collection of information unless it displays a currently valid OMB control number.

National Environmental Policy Act

We have determined that an Environmental Assessment or an Environmental Impact Statement as defined by the National Environmental Policy Act of 1969 need not be prepared in connection with regulations adopted pursuant to section 4(a) of the Act. A notice outlining our reason for this determination was published in the Federal Register on October 25, 1983 (48 FR 49244). This proposed rule does not constitute a major Federal action significantly affecting the quality of the human government.

Government to Government Relationship With Tribes

In accordance with the President's memorandum of April 29, 1994, “Government-to-Government Relations with Native American Tribal Governments “ (59 FR 22951), E.O. 13175, and Department of the Interior's manual at 512 DM 2, we readily acknowledge our responsibility to communicate meaningfully with recognized Federal Tribes on a government to government basis. We have determined that there are no Tribal lands essential for the conservation of the vernal pool crustaceans and plants addressed in this proposed rule because they do not support populations or suitable habitat. Therefore, critical habitat for these species has not been proposed for designation on Tribal lands.

References Cited

A complete list of all references cited herein, as well as others, is available upon request from the Sacramento Fish and Wildlife Office (see ADDRESSES section).

Authors

The primary authors of this notice are the staff of the Sacramento Fish and Wildlife Office (see ADDRESSES section).

List of Subjects in 50 CFR Part 17

• Endangered and threatened species
• Exports
• Imports
• Reporting and recordkeeping requirements
• Transportation

Proposed Regulation Promulgation

Accordingly, we propose to amend part 17, subchapter B of chapter I, title 50 of the code of Federal Regulations as set forth below:

PART 17—[AMENDED]

1. The authority citation for part 17 continues to read as follows:

Authority: 16 U.S.C. 1361-1407; 16 U.S.C. 1531-1544; 16 U.S.C. 4201-4245; Pub. L. 99-625, 100 Stat. 3500; unless otherwise noted.

2. In § 17.11(h) revise the entry for “Fairy shrimp, Conservancy,” “Fairy shrimp, longhorn,” “Fairy shrimp, vernal pool,” and “Tadpole shrimp, vernal pool” under “CRUSTACEANS” to read as follows: