California Code, Revenue and Taxation Code - RTC § 60507

All applications for refund provided under this article shall be filed within three years from the date of the purchase of the diesel fuel or, if the tax was not invoiced at the time of the purchase of the diesel fuel, the application for refund shall be filed within six months after the receipt of an invoice for the tax, whichever period expires later. Any application filed after the time prescribed shall not be considered for any purpose by the board, the Treasurer, or the state.