I’ve been to this canyon. A deep gash cut right through the middle of the Uncompaghre Plateau in western Colorado. And the mystery is, how did it form? There are only a couple of minor creeks that drain it.
In 1980, we were stripping 110 feet with a dragline, uncovering nice 7-8 feet of coal when we encountered a pocket of sand and gravel, missed by the exploration drill. The sand looked like a stack of gray/white shale, but went down past the fire clay that the coal was laying on. Since we couldn’t hold the highwall for the next cut, it was necessary to dig a box cut and leave a ledge of undistrurbed shale to continue mining the reserve. Our geologist believed this was a river channel void dating back to about the time the coal was formed, or about 250 million years.