California Code, Revenue and Taxation Code - RTC § 19311

(a)(1) If a change or correction is made or allowed by the Commissioner of Internal Revenue or other officer of the United States or other competent authority, a claim for credit or refund resulting from the adjustment may be filed by the taxpayer within two years from the date of the final federal determination (as defined in Section 18622or 18622.5), or within the period provided in Section 19306, 19307, 19308, or 19316, whichever period expires later.

(2) Within two years of the date of the final determination (as defined in Section 18622 or 18622.5) or within the period provided in Section 19306, 19307, or 19308, whichever period expires later, the Franchise Tax Board may allow a credit, make a refund, or mail to the taxpayer a notice of proposed overpayment resulting from the final federal determination.

(c)(1) For adjustments resulting in a tax imposed under paragraph (1) of subdivision (c) of Section 18622.5, paragraph (1) of subdivision (a) is modified by substituting “partnership” for “taxpayer.”

(2) This subdivision shall apply to final federal determinations assessed pursuant to amendments made to Subchapter C of Chapter 63 of the Internal Revenue Code  2 as in effect January 1, 2018.