Cal. Gov. Code § 50590

Proceedings for the formation of an open space maintenance district may be initiated by petition signed by the owners of assessable land in the proposed district, as shown by the last equalized assessment roll of the county, owning lands of an assessed value of not less than twenty-five percent (25%) of the total assessed value of all assessable land in the district, as shown by the last equalized county assessment roll. The petition shall contain a general description of the exterior boundaries of the proposed district, a general description of the open spaces to be maintained, a general description of the maintenance to be done on the open spaces, and a statement that the petition is filed pursuant to this chapter. The petition shall be filed with the clerk, who shall check or cause it to be checked. If it is signed by the requisite number of qualified signers, the clerk shall make his certificate to that effect and shall present the petition and certificate to the legislative body.