Cal. Gov. Code § 65916

Where there is a direct financial contribution to a housing development pursuant to Section 65915 through participation in cost of infrastructure, write-down of land costs, or subsidizing the cost of construction, the city, county, or city and county shall assure continued availability for low- and moderate-income units for 30 years. When appropriate, the agreement provided for in Section 65915 shall specify the mechanisms and procedures necessary to carry out this section.