It's based on where the river was in the 1840s, when Arlington (then Alexandria County) and Alexandria got sent back to VA. Basically, some idiot lawyer messed up. So part of the DCA runways are DC because a lot of that is landfill.
But yes, Roaches doesn't connect to Boundary Channel. That goes out via the entrance to the yacht dock near the Pentagon.
the wiki on Gravelly Point says it was owned by the Alexander Family (for whom Alexandria is named) and had a plantation - Abingdon - on it. There's occasional efforts to rename it after Nancy Reagan, I guess because why should Lady Bird get an island and Nancy be left out.
If you walk from the garages, I think A but it might be B, there's a historic ruin of part of Abingdon.
