Wash. Rev. Code § 84.34.210
Any county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, may acquire by purchase, gift, grant, bequest, devise, lease, or otherwise, except by eminent domain, the fee simple or any lesser interest, development right, easement, covenant, or other contractual right necessary to protect, preserve, maintain, improve, restore, limit the future use of, or otherwise conserve, selected open space land, farm and agricultural land, and timberland as such are defined in chapter 84.34 RCW for public use or enjoyment. Among interests that may be so acquired are mineral rights. Any county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, may acquire such property for the purpose of conveying or leasing the property back to its original owner or other person under such covenants or other contractual arrangements as will limit the future use of the property in accordance with the purposes of chapter 243, Laws of 1971 ex. sess.
RCW 84.34.210
Acquisition of interests in land for conservation, protection, preservation, or open space purposes by certain entities: RCW 64.04.130.
Property tax exemption for conservation futures on agricultural land: RCW 84.36.500.