California Code, Revenue and Taxation Code - RTC § 19314

(a) Notwithstanding any statute of limitations otherwise provided for in this part, any overpayment due a taxpayer for any year, shall be allowed as an offset in computing any deficiency in tax, for the same or any other year, if the overpayment results from any of the following:

(b) The offset provided under subdivision (a) shall not be allowed after the expiration of seven years from the due date of the return or returns on which the overpayment is determined.

(c) No refund shall be allowed under subdivision (a) unless before the period set forth in Section 19306 a claim therefor is filed by the taxpayer or unless before the expiration of that period the Franchise Tax Board has allowed a credit or made a refund.