California Code, Vehicle Code - VEH § 9557

(a) No penalty shall be imposed for delinquent payment of any fee required to be paid under this code in the event any instrument for effective payment of such fee is placed in the United States mail or in any postal box maintained by the United States Postal Service with sufficient identification in an envelope with postage thereon prepaid and addressed to the Department of Motor Vehicles at Sacramento, or to one of the regularly established branch offices of the department or to any person or organization authorized by the department under Section 4610, prior to the date or time the fee becomes delinquent.

(b) Any person so mailing an instrument for payment of any fee may file with the department a certificate in writing showing compliance with the provisions of this section. The certificate shall be accepted by the department as prima facie evidence of such mailing.