CA Rev & Tax Code Section 8101.1

For the purposes of subdivision (a) of Section 8101, the tax shall be refunded to any person with respect to fuel used in the operation of a motor vehicle on any highway which is under the jurisdiction of the United States Department of Agriculture and with respect to the use of such highway such person pays, or contributes to, the cost of construction or maintenance thereof pursuant to an agreement with or permission of, the United States Department of Agriculture.