Cal. Sts. & Hy. Code § 100.9
When any state highway is relocated in such a manner as to bypass a city or business district, the department shall erect and maintain appropriate directional signs, at the junction of the bypass and the road leading into such city or business district, and at a reasonable distance in advance of such junction, for the guidance of traffic desiring to enter the city or business district. Upon relinquishment of the bypassed highway to the county or city concerned, the signs, other than those designating the state or federal route number of such highway, previously erected on such highway shall be left in place by the department and thereafter shall be maintained by such county or city. When relinquishing any such bypassed highway, the department shall direct the attention of the county or city concerned to the provisions of this section regarding continued maintenance of such signs by the county or city.
Ca. Sts. and High. Code § 100.9