How to register a trailer with no VIN?

i bought a trailer from pepboys awhile back and never registered it. i purchased it at the counter and i lost the reciept. they didnt give me any paperwork with it and just handed it over. i tried looking for a VIN but no luck. i looked on the axel the neck, no luck. it looks street legal and it even has a place for license plates. how can i go about registering it in CA? anyone know? thanks!!