Cal. Rev. & Tax. Code § 41101

A refund shall not be approved by the department after three years from the last day of the second month following the close of the reporting period for which the overpayment was made, or, with respect to determinations made under Article 3 or 4 of Chapter 4 of this part, after six months from the date the determinations become final, or after six months from the date of overpayment, whichever period expires the later, unless a claim therefor is filed with the department within that period. A credit shall not be approved by the department after the expiration of that period unless a claim for credit is filed with the department within that period.