Cal. Gov. Code § 25550.7
Any property transferred to a city by a county pursuant to agreement or condition that said area be developed or maintained or both as a park, recreation or amusement area, whether under Section 25550 or Section 25550.5, may be modified by agreement of the city and county releasing said area in whole or part from such agreement or condition if the city agrees to devote said land so released to public purposes and the city also agrees to acquire, develop and maintain in perpetuity land mutually agreeable to the city and county of substantially the same value and develop and maintain the same exclusively to such purposes. Nothing contained in this section shall prohibit a city from purchasing or condemning any property interest of the county retained under Section 25550 or Section 25550.5. The county's interest in said land shall be valued for the purpose of sale or acquisition through condemnation at fee value of the land. Any money received by the county from such a transfer shall be used for park and recreation purposes.
Ca. Gov. Code § 25550.7