The old world rests there. So obviously it has to do with something eather pre war civilization or maybe ever arroyo. You cant discredit the theory based on distance alone in point lookout your over 400 miles away from dc.
No, but you can discredit it do to the fact that the city [i]still exists and is thriving [which means it is very alive and is doing very well][/i
LA was literally ruined and was turned into the Boneyard, which in turn became the Followers of the Apocolypses home. I remember hearing an NPC talking about it in New Vegas, and I think they said it turned into a bigger city. (This again means, it is still alive.)
It would make more sense for the Divide to be in northern Nevada, Utah or Idaho. (Untouched land, aside from Zion.)