California Code, Government Code - GOV § 65913.1

(a) In exercising its authority to zone for land uses and in revising its housing element pursuant to Article 10.6 (commencing with Section 65580) of Chapter 3, a city, county, or city and county shall designate and zone sufficient vacant land for residential use with appropriate standards, in relation to zoning for nonresidential use, and in relation to growth projections of the general plan to meet housing needs for all income categories as identified in the housing element of the general plan.  For the purposes of this section:

(b) Nothing in this section shall be construed to require a city, county, or city and county in which less than 5 percent of the total land area is undeveloped to zone a site within an urbanized area of that city, county, or city and county for residential uses at densities that exceed those on adjoining residential parcels by 100 percent.  For the purposes of this section, “urbanized area” means a central city or cities and surrounding closely settled territory, as defined by the United States Department of Commerce Bureau of the Census in the Federal Register, Volume 39, Number 85, for Wednesday, May 1, 1974, at pages 15202-15203, and as periodically updated.