Cal. Rev. & Tax. Code § 60502.2
Notwithstanding the refund provided for by Section 60502 and the exemption provided for by subparagraph (B) of paragraph (5) of subdivision (a) of Section 60100, any exempt bus operation using diesel fuel on which the tax has been refunded under Section 60502 or exempt from tax under subparagraph (B) of paragraph (5) of subdivision (a) of Section 60100 shall, for the privilege of operating buses on state highways and freeways, make a payment equal to one cent ($0.01) for each gallon of the refunded or 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.
Ca. Rev. and Tax. Code § 60502.2