California Code, Revenue and Taxation Code - RTC § 19311.5

(a) If any taxes paid to another state result in an allowable credit under Section 18001, 18002, 18003, 18004, 18005, or 18006, a claim for credit or refund of an overpayment of income tax attributable to a credit allowable under any of these sections may be filed within one year from the date tax is paid to the other state or within the period provided in Section 19306, whichever period expires later.

(b) This section shall apply to taxes paid to another state on or after January 1, 2009.