Cal. Rev. & Tax. Code § 19350

If a credit or refund of any part of an overpayment would be barred under Section 19306, except for Section 19312, no interest shall be allowed or paid with respect to that part of the overpayment for any period beginning after the expiration of the period of limitation provided in Section 19306 for filing claim for credit or refund of that part of the overpayment and ending at the expiration of six months after the date on which the claim was filed or, in case no claim was filed and the overpayment was found by the board, ending at the time the appeal was filed with the board.