California Code, Vehicle Code - VEH § 17154

If the bailee of an owner with the permission, express or implied, of the owner permits another to operate the motor vehicle of the owner, then the bailee and the driver shall both be deemed operators of the vehicle of the owner within the meaning of Sections 17152 and 17153.

Every bailee of a motor vehicle is liable and responsible for death or injury to person or property resulting from a negligent or wrongful act or omission in the operation of the motor vehicle, in the business of the bailee or otherwise, by any person using or operating the same with the permission, express or implied, of the bailee.