CA Veh Code Section 25103

Whenever the load upon any vehicle extends from the left side of the vehicle one foot or more, there shall be displayed at the extreme left side of the load during darkness:

(a)

An amber lamp plainly visible for 300 feet to the front and rear of the vehicle.

(b)

An amber lamp at the front visible for 300 feet to the front and a red lamp at the rear plainly visible for 300 feet to the rear of the vehicle if the projecting load exceeds 120 inches in length. The lamp shall not contain a bulb rated in excess of six candlepower.