California Code, Vehicle Code - VEH § 4458

If both license plates or a permanent trailer identification plate are lost or stolen, the registered owner shall immediately notify a law enforcement agency, and shall immediately apply to the department for new plates in lieu of the plates stolen or lost. The department shall in every proper case, except in the case of plates which are exempt from fees, cause to be issued applicable license plates of a different number and assign the registration number to the vehicle for which the plates are issued.