Cal. SHC § 820

The State of California assents to the provisions of Title 23 of the United States Code, as amended and supplemented, other acts of Congress relative to federal aid, or other cooperative highway work, or to emergency construction of public highways with funds apportioned by the government of the United States. All work done under the provisions of Title 23 or other acts of Congress relative to highways shall be performed as required under acts of Congress and the rules and regulations promulgated thereunder. Laws, or rules and regulations, of this state inconsistent with the laws, or rules and regulations, of the United States, shall not apply to that work, to the extent of the inconsistency.