California Code, Public Resources Code - PRC § 5563

If, in the opinion of the board, any land or property owned by the district, or any interest therein, becomes unnecessary for the purposes of the district, the board may, subject to the provisions of Section 5540, sell such lands or property, or interest therein. When land or property is temporarily unnecessary for park or open-space purposes, it may be leased for other purposes for a term not exceeding 25 years with an express provision in the lease that should the board by ordinance determine to use the lands for park, open-space, or other district purposes, the lease shall thereby be terminated. The proceeds of any sale or lease of lands or property, or any interest therein, shall be used for and applied to such purposes of the district as the board may, by resolution, determine.