From the plaque:
Plank Road, 1914 to 1927
This unique plank road, seven
miles long, was the only means early motorists had of
crossing the treacherous Imperial sand dunes. The eight by twelve foot
sections were moved with a team of horses whenever the
shifting sands covered portions of the road. Double sections
were placed at intervals to permit vehicles to pass.
Plaque placed by the State Department of Parks and Recreation in cooperation with the Imperial Valley Pioneer Association, October 16, 1971.