The state tax withheld should be reported on line 17 on your W-2 form. That is the only place you need to report it. You need to file a non-resident tax return for California to account for it on the state tax return. It will be populated by the entries on your federal tax return, plus you'll need to go through it to answer numerous questions. Your W-2 should list "CA" in box 15 and the state wages would be listed in box 16.