Cal. Gov. Code § 25561
The board of supervisors of any county, by ordinance, may adandon land, lying outside of the corporate limits of any city, which land has been dedicated for park purposes, by the recording of a subdivision plat or map in the recorder's office, upon finding that such land is not generally used by the public for park purposes, that no public funds have been expended to improve the same as a park, that no consideration has been paid for such land by any public agency, and that the public interest will be served by such abandonment. A recital in any ordinance enacted under this section that the board of supervisors finds that such facts exist shall be conclusive evidence of the existence thereof in favor of any subsequent purchaser of said lands for a valuable consideration.
After such abandonment, any interest in such land owned by the county may be sold by the board of supervisors in the same manner as other real property owned by the county and not required for county purposes may be sold.
No abandonment of any land dedicated for park purposes pursuant to this section, nor any sale of such land pursuant to this section, shall in any wise affect or impair any private easement or other right in or to or over said lands acquired or owned by any private person or corporation.
Ca. Gov. Code § 25561