California Code, Government Code - GOV § 54232

Land retained or transferred for public park and recreational purposes pursuant to Section 54231 shall be developed within 10 years, and shall be used for at least 25 years, following such retention or transfer for such purposes in accordance with the general plan for the city or county in which the land is located.  Otherwise, the land shall be sold by the local agency, and the funds received from the sale shall be used for highway purposes.  If the land originally had been transferred for such purposes, it shall revert to the original acquiring local agency for such sale.