Cal. Sts. & High. Code § 26114

For the purposes of this part the district may take over, control, operate, and use in whole or in part any county road or public highway and may construct any boulevard in whole or in part, over, along, or upon all or any part of any county road or public highway. District funds may be expended in the improvement of such road or highway to conform to the width and general character of the balance of the boulevard.