Cal. Gov. Code § 54233.5
If a local agency that is a district, excepting those whose primary mission or purpose is to supply the public with a transportation system, disposes of surplus land where local zoning permits development of 10 or more residential units or is rezoned within five years of the disposal to permit the development of 10 or more residential units, and 10 or more residential units are developed on the property, not less than 15 percent of the total number of residential units developed on the parcel shall be sold or rented at affordable housing cost, as defined in Section 50052.5 of the Health and Safety Code, or affordable rent, as defined in Section 50053 of the Health and Safety Code, to lower income households as defined in Section 50079.5 of the Health and Safety Code. Rental units shall remain affordable to, and occupied by, lower income households for a period of at least 55 years for rental housing and 45 years for ownership housing. The initial occupants of all ownership units shall be lower income households, and the units shall be subject to an equity sharing agreement consistent with the provisions of paragraph (2) of subdivision (c) of Section 65915. These requirements shall be contained in a covenant or restriction recorded against the restriction and each successor in interest who continues the violation, by any of the entities described in subdivisions (a) to (f), inclusive, of Section 54222.5. This section shall not apply to projects as defined in subdivision (j) of Section 32121 of the Health and Safety Code. A local agency shall provide a copy of any restrictions recorded against the property to the Department of Housing and Community Development in a form prescribed by the department.
Ca. Gov. Code § 54233.5