Cal. Veh. Code § 21455

If an official traffic control signal is erected and maintained at a place other than an intersection, including a freeway or highway on ramp, this article applies, except those provisions that by their nature can have no application. A stop required shall be made at a sign, crosswalk, or limit line indicating where the stop shall be made, but, in the absence of that sign or marking, the stop shall be made at the signal.