California Code, Vehicle Code - VEH § 35103

(a) A vehicle used for recreational purposes may exceed the maximum width established under Section 35100 if the excess width is attributable to an appurtenance, excluding a safety device, that does not exceed six inches beyond either sidewall of the vehicle.

(b) For the purposes of subdivision (a), an appurtenance is an integral part of a vehicle and includes, but is not limited to, awnings, grab handles, lighting equipment, cameras, and vents.  An appurtenance may not be used as a load carrying device.