Cal. Wat. Code § 25509
Where the assessor possesses a complete, accurate map of any land or where such a complete, accurate map of any land prepared for county purposes pursuant to Section 325 or 327 of the Revenue and Taxation Code is possessed by the assessor, he may number or letter the parcels or adopt the parcel numbers or letters used by the county assessor, and may renumber or reletter the parcels or prepare new map pages for any portion of such map to show combinations or divisions of parcels. Upon the board approving such maps and the manner of numbering and lettering the parcels, the parcel numbers and letters may be used in lieu of other description of the land involved in the assessment book, equalization of the assessments, assessment bills, if any, receipts for payment of assessments, published lists of delinquencies, certificates of sale, and in all other assessment proceedings and documents; except that land shall not be described in collector's deeds or other deeds by reference to any such map unless such map has been filed for record in the office of the county recorder of the county in which such land is located.
Any such map used for assessment purposes, or a copy thereof, shall at all times be publicly displayed in the office of the assessor.
Ca. Water Code § 25509