DC Boundary Stone Northwest Mile 1,that is the stone 1 mile northwest of the westernmost point in the original District of Columbia.  Actually it is now in northern Virginia. The stone was placed in 1791-1792 by Andrew Ellicott and Benjamin Banneker. See zhurnaly.com/maps/DC_Boundary_Stones.html for a map of these stones.
zhurnaly (Mark Zimmermann)
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