The Allegheny... and other river I don't know the names of, flow into the Ohio river, so they go west. The potomac is a smallish river that starts in West Virginia from a mountain source.
Edit: There are also only two rivers, their meeting point is referee to as a triangle. (There is a specific name for it)
Edit: There are also only two rivers, their meeting point is referee to as a triangle. (There is a specific name for it)
Seriously though, I don't know squat about American geology, I just remember that part vaugely being described in a game I played 1.5 years ago.