California Code, Revenue and Taxation Code - RTC § 19324

(a) Except as provided in subdivision (b), at the expiration of 90 days from the mailing of the notice, the Franchise Tax Board's action upon the claim is final unless within the 90-day period the taxpayer appeals in writing from the action of the Franchise Tax Board to the board.

(b) If within the period set forth in Section 19384 for filing a suit for refund the Franchise Tax Board receives information which it determines clearly establishes that a disallowed claim should have been allowed, in whole or in part, the Franchise Tax Board shall credit the amount of the overpayment against any taxes due from the taxpayer under this part and the balance shall be refunded to the taxpayer.