California Code, Revenue and Taxation Code - RTC § 60205.5

(a) Each government entity shall prepare and file with the board a return in the form as prescribed by the board, which may include, but not be limited to, electronic media showing the total number of gallons of dyed diesel fuel and undyed diesel fuel used in a diesel-powered highway vehicle during each calendar month, or the monthly period ending during the calendar month covered by the return, and any other information as the board deems necessary for the proper administration of this part. The person shall file the return on or before the last day of the calendar month following the monthly period to which it relates, together with a remittance payable to the board for the amount of tax due for that period. To facilitate the administration of this part, the board may require the filing of the returns for other than monthly periods.Returns shall be authenticated in a form or pursuant to methods as may be prescribed by the board.

(b) A government entity that has paid diesel fuel tax to a retail vendor that sold the diesel fuel to the government entity shall be allowed a credit on its tax return for the tax paid to the retail vendor.