One of America's most historic waterways. Rising at Fairfax Stone in West Virginia, the Potomac runs 405 miles, forming the border between Virginia and Maryland. Washington, D.C. was sited on the Potomac at its confluence with the Anacostia River. George Washington's plantation Mount Vernon was on the Potomac, while Robert E. Lee's two invasions north of the Potomac were major events of the Civil War.