Wow. You build dams and you still asked that question about the Colorado River Delta? Just wow.
Well of course. In my business, you don't look at the visually obvious and make declarations.
As I said, that pretty sounding description full of assumptions you posted doesn't hold up to fact. The 'silt layer' is no were near thick enough to account for the amount of earth "erroded" out of the grand canyon. it's more consistent with the silt accumulated by a lake that once existed in the area.