Cal. Bus. & Prof. Code § 5499
Regardless of any other provision of this chapter or other law, no city or county shall require the removal of any on-premises advertising display on the basis of its height or size by requiring conformance with any ordinance or regulation introduced or adopted on or after March 12, 1983, if special topographic circumstances would result in a material impairment of visibility of the display or the owner's or user's ability to adequately and effectively continue to communicate with the public through the use of the display. Under these circumstances, the owner or user may maintain the advertising display at the business premises and at a location necessary for continued public visibility at the height or size at which the display was previously erected and, in doing so, the owner or user is in conformance.
Ca. Bus. and Prof'l. Code § 5499