Cal. Vehicle Code § 25803

(a) All vehicles not otherwise required to be equipped with headlamps, rear lights, or reflectors by this chapter shall, if operated on a highway during darkness, be equipped with a lamp exhibiting a red light visible from a distance of 500 feet to the rear of the vehicle. In addition, all of these vehicles operated alone or as the first vehicle in a combination of vehicles, shall be equipped with at least one lighted lamp exhibiting a white light visible from a distance of 500 feet to the front of the vehicle. (b) A vehicle shall also be equipped with an amber reflector on the front near the left side and a red reflector on the rear near the left side. The reflectors shall be mounted on the vehicle not lower than 16 inches nor higher than 60 inches above the ground and so designed and maintained as to be visible during darkness from all distances within 500 feet from the vehicle when directly in front of a motor vehicle displaying lawful lighted headlamps undimmed. (c) In addition, if a vehicle described in subdivision (a) or the load thereon has a total outside width in excess of 100 inches there shall be displayed during darkness at the left outer extremity at least one amber light visible under normal atmospheric conditions from a distance of 500 feet to the front, sides, and rear. At all other times there shall be displayed at the left outer extremity a solid red or fluorescent orange flag or cloth not less than 18 inches square.