Black Canyon of the Gunnison

Colorado, looking upstream. The Gunnison River flows westward from the Rockies, joining the Colorado River at Grand Junction, Colorado. Here it has carved an extraordinary deep gorge, in some places deeper than it is wide, in extremely hard metamorphic rock seamed with granite. This is an example of what's called, in the jargon, a "superposed" drainage. The metamorphic rock is in an uplifted block, part of the so-called "Ancestral Rockies", that had been buried under sedimentary rock. The Gunnison had eroded down thru this sedimentary cover, and perforce kept cutting when it encountered the underlying hard rock. Ironically, had the ancestral Gunnison been a few miles south it would have missed this block and the Canyon wouldn't exist!

The most famous section of the Black Canyon is its western part, site of the eponymous national park. The Canyon continues upstream another dozen miles or so beyond the park, though, where it's mostly paralleled on the north by Colorado SR 92. These pix were taken at Pioneer Point Overlook, just off that highway. Morrow Point Dam, just upstream from the park, backs up Morrow Point Reservoir in this part of the Black Canyon--hence the water extending wall to wall in the right inset--but the reservoir lies far enough below the canyon rim that the esthetics aren't too impaired.