Cal. Rev. & Tax. Code § 60021

“Entry” means the importing of diesel fuel into this state. However, diesel fuel brought into this state in the fuel tank of a motor vehicle shall not be deemed to be an “entry” if not removed from the fuel tank except as used for the operation of that motor vehicle, except to the extent that diesel fuel was acquired tax free for export or a refund of tax was claimed as a result of exportation from the state from which that diesel fuel was transported into this state.