How much you get back depends on your entire tax situation, filing status, etc. You will need to file a CA Non-Resident tax return for that income. Prepare the CA return first, then your resident state. Often, your resident state will give a credit for taxes paid to a non-resident state on income that is taxed in both states.
How to file a non-resident state return?
https://ttlc.intuit.com/replies/3302052