Cal. Sts. & Hy. Code § 93
The department may construct and maintain detours as may be necessary to facilitate movement of traffic where state highways are closed or obstructed by construction or otherwise. The department may direct traffic onto any other public highway which will serve as a detour, in which case the department, upon the completion of such use, and upon the request of the local agency having jurisdiction over the highway, shall restore the same to its former condition; provided, that the local agency shall reimburse the department for the amount of all betterment to such highway caused by the restoration. The department shall also reimburse the local agency for all reasonable additional expenses incurred by that agency in maintaining said highway during the period of detour if such additional expenses were caused by said detour.
Ca. Sts. and High. Code § 93