Fairfax Stone Historical Monument State Park preserves the site of the Fairfax Stone at the source of the North Branch of the Potomac River in West Virginia. Established in 1746 during a survey by Colonel Peter Jefferson and Thomas Lewis, the stone marked the beginning of the Fairfax Line and helped define the vast Fairfax Grant claimed by Thomas Fairfax. Resurveyed in 1748 by George Washington and David Morgan, it remained important in later boundary disputes, though it was not a direct point on the Maryland border. Replaced multiple times after weathering, relocation, and vandalism, the site remained legally significant until Maryland v. West Virginia in 1910.