Cal. Veh. Code § 34501.4

Any driver subject to the hours of service limitations and logbook requirements of this division, who is unable to produce upon request of a representative of the department any driver’s logbook or is only able to produce an incomplete driver’s log book for the prior 24-hour period, is rebuttably presumed to be in violation of the hours of service limitations in Sections 34501 and 34501.2.