No tax shall be imposed on any user 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 the user 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.
Source:
Section 8653.1, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=RTC§ionNum=8653.1..