Vehicle Code § 22509
CHAPTER 9. Stopping, Standing, and Parking
Local authorities within the reasonable exercise of their police powers may adopt rules and regulations by ordinance or resolution providing that no person driving, or in control of, or in charge of, a motor vehicle shall permit it to stand on any highway unattended when upon any grade exceeding 3 percent within any business or residence district without blocking the wheels of the vehicle by turning them against the curb or by other means.