Cal. Sts. & High. Code § 967

Whenever a right of way for a highway is conveyed to a county and the sole consideration for the conveyance is an agreement by the county to construct and maintain a highway on the right of way and to construct highway fences on the right of way boundaries, and thereafter such right of way becomes a county highway, the board of supervisors may, within five years from the date of such conveyance, construct highway fences along the boundaries of such right of way.