Cal. Bus. & Prof. Code § 5227
It is the intention of the Legislature to occupy the whole field of regulation by the provisions of this chapter except that nothing in this chapter prohibits enforcement of any or all of its provisions by persons designated so to act by appropriate ordinances duly adopted by any county of this state nor does anything prohibit the passage by any county of reasonable land use or zoning regulations affecting the placing of advertising displays in accordance with the provisions of the Planning Law, Chapter 1 (commencing with Section 65000) of Title 7 of the Government Code, relating to zoning, or, with reference to signs or structures pertaining to the business conducted or services rendered or goods produced or sold upon the property upon which such advertising signs or structures are placed, ordinances subjecting such signs or structures to building requirements.
Ca. Bus. and Prof'l. Code § 5227