Cal. Rev. & Tax. Code § 60108

Notwithstanding the exemption provided for in subparagraph (D) of paragraph (5) of subdivision (a) of Section 60100, any government entity using diesel fuel exempt from tax under subparagraph (D) of paragraph (5) of subdivision (a) of Section 60100 shall, for the privilege of operating diesel-powered highway vehicles on highways in this state, make a payment equal to the tax specified in Section 60050 for each gallon of exempt diesel fuel used. The payments required by this subdivision shall be paid to the State Board of Equalization in the manner prescribed by the board, and the payments shall be treated as a tax for all purposes of this part.