[medved]

Just to doublecheck the numbers, you've put the average depth of the Grand Canyon at 2000 feet (I've heard some section are as much as a mile deep, but 2000 feet sounds like a good average).

The 1500' - 2000' number I was throwing out is not the depth of the thing but only the visual impression one gets of how far the thing goes more-or-less straight down before starting to slope inwards at all.

Reading about this one in books doesn't get it. If you've never seen it up close, you need to. The most major impression you get is of the sharp and jagged and pristine look of all the rocks in that initial 1500' drop. Rivers don't do that. If the thing had been cut by water, it would be totally smooth. The thing basically defies any sort of uniformitarian geology.

[Junior]

Why wouldn't rivers cut straight down through rock? When I use to hike in the north Georgia mountains I often ran across gorges cut by streams. Some of these gorges had shear vertical walls going up several meters. In some cases, the rock walls actually angled inward. The granite walls were not worn any smoother than the rocks I find in my back yard. I'm not sure the Grand Canyon really requires anything more than water erosion (and maybe the occasional sand blasting by wind) to account for its formation.

[VadeRetro]

The most major impression you get is of the sharp and jagged and pristine look of all the rocks in that initial 1500' drop. Rivers don't do that.

"Smooth" is a silly strawman. You have finely layered sediments. They're going to cleave and crumble all over the place and they did.