Many of the erosion features that make no sense given current water flows suddenly become logical when you consider ice age melt.
The Colorado river has cut canyons all the way up to where it begins. Also when you drive through a river valley that goes south from the glacial areas, you see that the modern river actually winds between ancient river banks that are sometimes miles wide. There are no current flooding levels that come close to explaining those ancient river banks.
This morning the little creek that borders my land is running like a roaring freight train,and is carrying a lot of dirt and debris. normally only a foot or two deep and maybe ten feet wide is is out of its banks and running a couple hundred feet wide ! All because of about six hours of intense rainstroms in the area;now think about what 40 days and 40 nights of rain might do!!!
Colorado River begins at Granby, CO, just south of Rocky Mountain Nat Park and goes west towards Steamboat Springs, been there. What about Black Canyon of the Gunnison?