Cal. Rev. & Tax. Code § 60503.1

If a purchaser gives a Section 60503 exemption certificate to an ultimate vendor to the effect that the diesel fuel purchased will be used on a farm for farming purposes or in an exempt bus operation, and sells the diesel fuel or uses the diesel fuel in some other manner or for some other purpose, the purchaser will be liable for payment of the tax under Chapter 2 (commencing with Section 60050) of this part. The tax, applicable penalties, and interest shall become due and payable and shall be ascertained and determined in the same manner as the backup tax under Section 60361.5.