California Code, Revenue and Taxation Code - RTC § 6902

(a)(1) Forpersons required to file returns on other than an annual basis, except as provided in subdivision (b) no refund shall be approved by the board after three years from the last day of the month following the close of the quarterly period for which the overpayment was made, or, with respect to determinations made under Article 2 (commencing with Section 6481), Article 3 (commencing with Section 6511), or Article 4 (commencing with Section 6536) of Chapter 5 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 board within that period.

(2) Forpersons required to file returns on an annual basis, except as provided in subdivision (b) no refund shall be approved by the board after three years from the last day of the calendar month following the one-year period for which the overpayment was made, or with respect to determinations made under Article 2 (commencing with Section 6481), Article 3 (commencing with Section 6511), or Article 4 (commencing with Section 6536) of Chapter 5, 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 board within that period. No credit shall be approved by the board after the expiration of that period unless a claim for credit is filed with the board within that period, or unless the credit relates to a period for which a waiver is given pursuant to Section 6488.