California Code, Vehicle Code - VEH § 26451

(a) The parking brake shall be adequate to hold the vehicle or combination of vehicles stationary on any grade on which it is operated under all conditions of loading on a surface free from snow, ice or loose material.  In any event the parking brake shall be capable of locking the braked wheels to the limit of traction.

(b) The parking brake shall be applied either by the driver's muscular efforts, by spring action, or by other energy which is isolated and used exclusively for the operation of the parking brake or the combination parking brake and emergency stopping system.

(c) The parking brake shall be held in the applied position solely by mechanical means.