We were watching The History Channel a couple of days ago and one of the boundary stones of the original District of Columbia was shown on-site in the seawall just south of Jones Point, VA Lighthouse. Lighthouse Friends description of Jones Point Light indicates it was installed by George Washington. A marker designating the boundary between Maryland/Virginia is located north of the lighthouse.

This link gets you to pictures and some of the historical information:

http://oha.alexandriava.gov/archaeology/jonespoint/ar-jpt-dc.html