California Code, Vehicle Code - VEH § 24608

(a) Motortrucks, trailers, semitrailers, and buses 80 or more inches in width manufactured on or after January 1, 1968, shall be equipped with an amber reflector on each side at the front and a red reflector on each side at the rear. Any vehicle may be so equipped.

(b) Motortrucks, trailers, semitrailers, housecars, and buses 80 or more inches in width and 30 or more feet in length manufactured on or after January 1, 1968, shall be equipped with an amber reflector mounted on each side at the approximate midpoint of the vehicle. Any such vehicle manufactured prior to January 1, 1968, may be so equipped.

(c) Required reflectors on the sides of vehicles shall be mounted not lower than 15 inches nor higher than 60 inches. Additional reflectors of a type meeting requirements established by the department may be mounted at any height.

(d) Reflectors required or permitted in subdivisions (a) and (b) shall be so maintained as to be plainly visible at night from all distances within 600 feet to 100 feet from the vehicle when directly in front of lawful upper headlamp beams.

(e) Area reflectorizing material may be used in lieu of the reflectors required or permitted in subdivisions (a) and (b), provided each installation is of sufficient size to meet the photometric requirement for such reflectors.