A smog check from Oregon will not be accepted in California. Not to worry though. The DMV will renew the vehicle's registration without a smog check if a form REG 5103 is submitted along with the registration renewal. The REG 5103 allows vehicle owners whose vehicles are currently and temporarily located out of state to bypass the smog check requirement. The form does however require that the vehicle be administered a smog check as soon as it returns back to California.
Simply fill out and sign (registered owner) DMV's "Statement of Facts" form (Section G), OR complete Reg 5103, explaining your vehicle is out of state and the registration tags will be mailed to the DMV address on record. You can obtain a Temporary Smog Exemption (Reg 5103) by downloading it here.
More Info on How to Renew Vehicle Registration in California When Out-of-State.
