|The formation of this canyon near Gunnison, CO is unexpected
because just a few miles to either the north or south lie much softer
rocks for the Gunnison River to erode. The explanation for the river
at this location is that it started to flow in this location, making a
small river valley. Later as the mountains were formed as part of the
Laramide Orogeny, the mountain building process that formed the Rocky
Mountains, the land was uplifted and the river valley along with it.
Because the change in gradient (slope) increased the river did most of
it's erosion by downcutting. As more of the hard rock was downcut and
the rocks continued to be uplifted the river didn't have any other
place to go. See this page from the
National Park Service for more information on the formation of
nearby mountains and the uplifting that caused the canyon. The canyon
continues to erode downward at the rate of about one inch per century.
At the rate of one inch per century how long does it take to dig a
2,000 foot canyon?