California Code, Revenue and Taxation Code - RTC § 6459

(a)(1) Except as provided in subdivisions (b) and (c), the board for good cause may extend for not to exceed one month the time for making any return or paying any amount required to be paid under this part. The extension may be granted at any time provided a request therefor is filed with the board within or prior to the period for which the extension may be granted.

(2) Any person to whom an extension is granted shall pay, in addition to the tax, interest at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the date on which the tax would have been due without the extension until the date of payment.

(b)(1) The board may grant an extension for more than one month if both of the following conditions occur:

(2) Any extension granted under this subdivision shall expire no later than the last day of the month following the month in which the budget is adopted or one month from the due date of the return or payment, whichever comes later.

(3) Any person to whom an extension has been granted under this subdivision shall pay, in addition to the tax, interest at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the date on which the tax would have been due without the extension until the date of payment. However, no interest shall be due on that portion of the payment equivalent to the amount due to the person from the state on the due date of the payment.

(c)(1) In the case of a disaster, the board, for a period not to exceed three months, may extend the time for making any report or return or paying any tax required under this part. The extension may be granted at any time provided a request therefor is filed with the board within or before the period for which the extension may be granted.

(2) Any person to whom an extension is granted shall pay, in addition to the tax, interest at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the date on which the tax would have been due without the extension until the date of payment.

(3) For purposes of this section, “disaster” means fire, flood, storm, tidal wave, earthquake, or similar public calamity, whether or not resulting from natural causes.