Cal. BPC § 5419

(a) The director shall seek agreement with the Secretary of Transportation of the United States, or his successor, under provisions of Section 131 of Title 23 of the United States Code, to provide for effective control of outdoor advertising substantially as set forth herein, provided that such agreement can vary and change the definition of “unzoned commercial or industrial area” as set forth in Section 5222 and the definition of “business area” as set forth in Section 5223, or other sections related thereto, and provided further that if such agreement does vary from such sections it shall not be effective until the Legislature by statute amends the sections to conform with the terms of the agreement. If agreement is reached on these terms, the director shall execute the agreement on behalf of the state.

(b) In the event an agreement cannot be achieved under subdivision (a), the director shall promptly institute proceedings of the kind provided for in subdivision (l) of Section 131 of Title 23 of the United States Code, in order to obtain a judicial determination as to whether this chapter and the regulations promulgated thereunder provide effective control of outdoor advertising as set forth therein. In such action the director shall request that the court declare rights, status, and other legal relations and declare whether the standards, criteria, and definitions contained in the agreement proposed by the director are consistent with customary use. If such agreement is held by the court in a final judgment to be invalid in whole or in part as inconsistent with customary use or as otherwise in conflict with Section 131 of Title 23 of the United States Code, the director shall promptly negotiate with the Secretary of Transportation, or his successor, a new agreement or agreements which shall conform to this chapter, as interpreted by the court in such action.