California Vehicle Code section 12500 provides:
A person may not drive a motor vehicle, a motorcycle, or motorized bicycle upon a highway or upon any off-street parking facility, unless the person then holds a valid driver’s license issued under this code, except those persons who are expressly exempted under this code.
A violation of this vehicle code could be charged as an infraction or a misdemeanor. For infractions, the fine is $250 and for misdemeanors, you could be sentenced to jail for up to 90 days.