At the headspring of the Potomac River stands one of America’s historic spots, named for Thomas Lord Fairfax, who owned all the land between the Potomac and Rappahannock rivers. The first Fairfax Stone, marked by "FX," was set in 1746 by Thomas Lewis, a surveyor employed by Lord Fairfax, and it serves as the base point for the western dividing line between Maryland and West Virginia.