Hi.

Here's one of the photos I took - it's the mark which is what I called
the tri-point marker - it is not one that is in the lighthouse.
When one stands above the pictured marker, and one looks off 45% east of
north (i.e., to the northwest, and can follow the DC-MD border line on
the maps and easily see that from that point, where the eastern end of
the District of Columbia's portion of the Wilson Bridge, 200 meters
distant, is. The District's western border on the bridge is right
above the shore of the Potomac. If one walks north of this stone, to
try to locate another spot from which the 45 degree border would depart
NE from the shoreline, there is nothing to be found. At low watermark,
but yesterday six feet from shore at high tide, immediately east of this
stone, there is a DC maritime navigation sign. If there was some other
border marker north of this stone from which the DC-MD border starts out
heading NE, this sign would have to be in Maryland. Though the marker
has a triangle on top, it doesn't mention all three entities, meaning to
me that the triangle has no significance. There are no markings on the
sides of the stone itself.

I'll keep you posted.

Regards
LN