Cal. Revenue and Taxation Code § 19033

(a) If the Franchise Tax Board determines that the tax disclosed by the taxpayer on an original or amended return, including an amended return reporting federal adjustments pursuant to Section 18622, is less than the tax disclosed by its examination, it shall mail notice to the taxpayer of the deficiency proposed to be assessed. In no case shall the determination of the deficiency be arbitrary or without foundation. (b) (1) Except as provided in paragraph (2), the Franchise Tax Board, in connection with the determination described in subdivision (a), shall examine the original or amended return or related electronically stored return data. (2) If the return or return data described in paragraph (1) has been destroyed or cannot be located after reasonable effort, the Franchise Tax Board shall request the taxpayer to provide a paper or electronic copy of the return. If the taxpayer fails to provide a copy within 30 days, which may be extended an additional 30 days for reasonable cause, from the date of the request, paragraph (1) shall not apply. (c) As used in this section, “electronically stored return data” means an electronic record of line items from an original or amended return and accompanying schedules that is routinely created as a return is processed. (d) The amendments to this section made by Chapter 414 of the Statutes of 2000 shall apply to notices of deficiencies proposed to be assessed issued on or after January 1, 2001. (e) The notice described in subdivision (a) shall be mailed in a manner that includes a postmark. For purposes of this subdivision, postmark means a postal marking made on a letter, package, or postcard indicating the date on which the item is delivered to the United States Postal Service. (f) The amendments made to this section by the act adding this subdivision shall apply to notices of deficiencies proposed to be assessed issued on or after January 1, 2008.