California Code, Revenue and Taxation Code - RTC § 6471

(a) Upon written notification by the board, any person whose estimated measure of tax liability under this part averages seventeen thousand dollars ($17,000) or more per month, as determined by the board, shall, without regard to the measure of tax in any one month, make prepayments as prescribed in this section.

(b) Persons engaged in their present business during all of the corresponding quarterly period of the preceding year, or persons who are successors to a business that was in operation during all of that quarterly period, may satisfy the above monthly prepayment requirements for the first, third, and fourth calendar quarters by payment of an amount equal to one-third of the measure of tax liability reported on the return or returns filed for that quarterly period of the preceding year multiplied by the state and local tax rate in effect during the month for which the prepayment is made.

These persons may satisfy their prepayment requirements for the second calendar quarter by making a first prepayment of an amount equal to one-third of the measure of tax liability reported, and a second prepayment of an amount equal to one-half of the measure of tax liability reported, on the return or returns filed for that quarterly period of the preceding year multiplied by the state and local tax rate in effect during the month for which the prepayment is made.

Prepayments shall be made during the quarterly periods designated by the board and during each succeeding quarterly period until further notified in writing by the board.