California Code, Revenue and Taxation Code - RTC § 19364

If any overpayment of tax is claimed as a credit against estimated tax for the succeeding taxable year, that amount shall be considered as payment of the tax for the succeeding year (whether or not claimed as a credit in the return of estimated tax for that succeeding year), and no claim for credit or refund of that overpayment shall be allowed for the taxable year in which the overpayment arises.