If you proceed with the purchase, you must complete the following steps within of bringing the vehicle into California to avoid late fees:
Buying a car in a sales tax state but registering/living ... - Claimyr
: You will be charged the tax rate of the California city or county where you reside.
: If you had paid sales tax in Oregon (which you won't), California would give you a credit for that amount. Since Oregon's rate is 0%, you will owe California the full amount .