California Code, Revenue and Taxation Code - RTC § 19049

(a) When a deficiency is determined and the assessment becomes final, the Franchise Tax Board shall mail notice and demand to the taxpayer for the payment thereof. The deficiency assessed is due and payable at the expiration of 15 days from the date of the notice and demand.

(b) The amendments made by Chapter 600 of the Statutes of 1997 are operative for notices issued on or after January 1, 1998.

(c) 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.

(d) The amendments made to this section by the act adding this subdivision are operative for notices issued on or after January 1, 2008.