Cal. RTC § 6292

(a) Except when the sale is by lease, when a mobilehome or commercial coach required to be registered annually under the Health and Safety Code or a vehicle required to be registered under the Vehicle Code is sold at retail by other than a person licensed or certificated pursuant to the Health and Safety Code or the Vehicle Code as a manufacturer, remanufacturer, dealer, dismantler, or lessor-retailer, subject to Section 11615.5 of the Vehicle Code, the retailer is not required or authorized to collect the use tax from the purchaser, but the purchaser of the vehicle shall pay the use tax to the Department of Housing and Community Development acting for and on behalf of the board pursuant to Section 18123 of the Health and Safety Code or to the Department of Motor Vehicles acting for and on behalf of the board pursuant to Section 4750.5 of the Vehicle Code.

(b) If the purchaser makes an application to either department which is not timely, and is subject to penalty because of delinquency in effecting registration or transfer of registration of the vehicle, he or she then becomes liable also for penalty as specified in Section 6591, but no interest shall accrue.

(c) Application to the appropriate department by the purchaser relieves the purchaser of the obligation to file a return with the board under Section 6452.

(d) If the purchaser does not make application to either department, or does not pay the amount of use tax due, or files a return with the board under Section 6455 which is not timely, interest and penalties shall apply with respect to the unpaid amount as provided in Chapter 5 (commencing with Section 6451).