California Code, Vehicle Code - VEH § 2802

(a) Any traffic officer having reason to believe that a vehicle is not safely loaded or that the height, width, length, or weight of a vehicle and load is unlawful may require the driver to stop and submit to an inspection, measurement, or weighing of the vehicle. The weighing may be done either by means of portable or stationary scales and the officer may require that the vehicle be driven to the nearest scale facility, in the event the scales are within five road miles.

(b) Selected inspection facilities and platform scales operated by the Department of the California Highway Patrol may, at the discretion of the commissioner, be open for extended hours, up to and including 24 hours every day. The primary purpose of the extended hours is to assist in the detection of overweight vehicles. These inspection facilities and platform scales shall be located near primary border route points of entry into the state and key routes within the state.

(c) An amount not to exceed one million dollars ($1,000,000) shall be available annually from the Motor Vehicle Account in the State Transportation Fund, upon appropriation by the Legislature, for the expanded operation of the scale facilities, as specified in subdivision (b). It is the intent of the Legislature that the funds made available pursuant to this subdivision shall be the only funds available for purposes of this section.