Cal. Rev. & Tax. Code § 43201

(a) If the California Department of Tax and Fee Administration is dissatisfied with the return or report filed or the amount of tax paid to the state by any taxpayer, or if no return or report has been filed or no payment or payments of the taxes have been made to the state by a taxpayer, the California Department of Tax and Fee Administration may compute and determine the amount to be paid, based upon any information available to it. In addition, where the California Department of Tax and Fee Administration is authorized to collect a tax for another state agency, the California Department of Tax and Fee Administration may issue a notice of determination or similar billing document for collection of the tax. One or more additional determinations may be made of the amount of tax due for one, or for more than one, period. The amount of tax so determined shall bear interest at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the date the amount of the tax, or any portion thereof, became due and payable until the date of payment. In making a determination, the California Department of Tax and Fee Administration may offset overpayments for a period or periods against underpayments for another period or periods and against the interest and penalties on the underpayments.
(b) If any part of the deficiency for which a determination of an additional amount due is found to have been occasioned by negligence or intentional disregard of this part or authorized regulations, a penalty of 10 percent of the amount of the determination shall be added, plus interest as provided above.
(c) If any part of the deficiency for which a determination of an additional amount due is found to be occasioned by fraud or an intent to evade this part or authorized regulations, a penalty of 25 percent of the amount of the determination shall be added, plus interest as provided in subdivision (a).
(d) The California Department of Tax and Fee Administration shall give to the taxpayer written notice of its determination. The notice shall be served in one of the following manners:
1. (1) By placing the notice in a sealed envelope, with postage paid, addressed to the taxpayer at their address as it appears in the records of the California Department of Tax and Fee Administration. Service made pursuant to this paragraph shall be deemed complete at the time of the deposit of the notice in a United States Post Office, or a mailbox, sub-post office, substation, or mail chute, or other facility regularly maintained or provided by the United States Postal Service without extension of time for any reason.
2. (2) By personally delivering the notice to the person to be served. Service made pursuant to this paragraph shall be deemed complete at the time of delivery. Personal service to a corporation may be made by delivery of a notice to any person designated in the Code of Civil Procedure to be served for the corporation with summons and complaint in a civil action.
3. (3)
  1. (A) By delivering the notice electronically via secure transmission when either of the following applies:
    1. (i) The taxpayer requests the notice of determination to be sent electronically via secure transmission.
    2. (ii) The California Department of Tax and Fee Administration has evidence that the taxpayer no longer receives mail at the address of record and has previously provided an address for electronic mail.
  2. (B) Service provided pursuant to subparagraph (A) shall be deemed complete at the time the California Department of Tax and Fee Administration electronically transmits the notice via the taxpayer’s secure web portal, without extension of time for any reason.
(e) This section shall not apply to any fee imposed pursuant to Section 25205.5 or 25205.5.2 of the Health and Safety Code for any return or payment that becomes due on or after November 30, 2024.