California Code, Vehicle Code - VEH § 27459

No person shall operate any motor vehicle, trailer or semitrailer upon any portion of a highway without tire traction devices when that portion of the highway is signed for the requirement of tire traction devices.  In any case where a passenger vehicle or motortruck having an unladen weight of 6,000 pounds or less may be required by the Department of Transportation or local authorities to be equipped with tire traction devices, the devices shall be placed on at least two drive wheels, or the department or local authorities may provide, in the alternative, that the vehicle may be equipped with snow-tread tires on at least two drive wheels when the weather and surface conditions at the time are such that the stopping, tractive, and cornering abilities of the snow-tread tires are adequate.  The snow-tread tires shall be of a type and design manufactured for use on snow as a replacement for tire chains or tire traction devices, shall be in good condition, and shall bear the marking of M-S, M/S, or other marking indicating that the tire was manufactured for use on snow, or, in the case of tires purchased before January 1, 1987, shall either bear the markings or, in the opinion of the inspecting officer, comply with the tread pattern requirements of Section 558.