Black Canyon of the Gunnison - Pt. 3

Weathering and Hydrology of the Canyon

The Black Canyon was formed relatively quickly over the last 2 million years by down-cutting very resistant Precambrian bedrock. Because the water had no choice, it was forced to cut through the canyon and the canyon floor continues to erode at a rate of 1 foot per thousand years.

(photo at left from http://wwa.colorado.edu/western_water_law/)

Because the metamorphosed granite is so resistant, the sides of the canyon weather and erode very slowly. However, some weathering does occur such as the freeze-thaw cycles that create frost action weathering that contributes to mass wasting of the canyon walls. In the steep areas of the canyon, large columns of rocks break away and form areas of talus in parts of the canyon

(the photo at right shows a dark, snowy area of talus).

The Gunnison River get its water from the snowmelt and limited rainfall of the Western slopes of the Continental Divide as it races through the Black Canyon to join the Colorado River. The Blue Mesa Dam creates a reservoir (see reservoir in photo below) that decreases the river’s erosion power but provides water for irrigation and public use on the western slope, as well as a place for recreation. The water from this river is a partially-renewable ground water resource that is a critical source for domestic water in the area.

Other sources:

http://www.ux1.eiu.edu/~cfrbj/parks/blca/blca2.htm

Some info on water rights in the area: http://www.waterinfo.org/gunnison-river

The Essential Guide to Black Canyon of the Gunnison National Park

By John Jenkins (p. 45) retrieved from http://books.google.com/books?id=W31yWpLZMxUC&pg=PA45&lpg=PA45&dq=black+canyon+weathering&source=bl&ots=xCohv3pL9l&sig=vnlwJmiCsSvg5FuxurEug43mdjU&hl=en&ei=qFabTavrDZTAsAPJubGIBA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCcQ6AEwAg#v=onepage&q=black%20canyon%20weathering&f=false