California Code, Vehicle Code - VEH § 14604

(a) No owner of a motor vehicle may knowingly allow another person to drive the vehicle upon a highway unless the owner determines that the person possesses a valid driver's license that authorizes the person to operate the vehicle.  For the purposes of this section, an owner is required only to make a reasonable effort or inquiry to determine whether the prospective driver possesses a valid driver's license before allowing him or her to operate the owner's vehicle.  An owner is not required to inquire of the department whether the prospective driver possesses a valid driver's license.

(b) A rental company is deemed to be in compliance with subdivision (a) if the company rents the vehicle in accordance with Sections 14608 and 14609 .