The Nankoweep delta is the first place where the walls widen out and the river is pretty wide. I would say 200-300 feet wide in places. Judging from my Martin and Whitis, that view is from around mile 53.5 and the bend in the river is around mile 57. You are correct about perspective in GC.
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Just because you don't take an interest in politics doesn't mean politics won't take an interest in you.... Pericles (430 B.C)