Colorado
The walls of the Black Canyon are from Earth’s basement: 1.7-billion-year-old metamorphic rocks cut through by lighter veins of pegmatite.
Visiting the bottom of the Black Canyon of the Gunnison is not for the timid, as the few poorly defined trails are steep and littered with large, unstable boulders that require careful scrambling.
No other major canyon system in North America equals the depth and darkness of the Black Canyon of the Gunnison. Depending on your altitude, it can be hard to appreciate from above just how deep and dark this precipitous gorge really is, but look for a series of manmade reservoirs that drop into a steep, narrow canyon.
The Gunnison River is a Colorado River tributary that drains parts of southwest Colorado and the Uncompahgre Plateau before joining the Colorado River in Grand Junction on its way into Utah. After flowing through a series of hydroelectric reservoirs near the town of Gunnison, the river enters the Black Canyon—so named because its high-walled depths only receive a few minutes of direct sunlight a day.
The sheer walls of the Black Canyon do indeed give it a foreboding appearance. Composed mainly of dark gneiss and schist dating back 1.7 billion years, during the Precambrian Period, these ancient rocks are crosscut by lighter-colored dikes of pegmatite that forced their way into the darker rocks around the same time period. The Gunnison River did not originally choose to carve its path through the very old, very hard rocks. It began its course around 15 million years ago, running through softer volcanic rocks that erupted during the Tertiary Period, between 35 and 26 million years ago.
Around 3 million years ago, a period of regional uplift raised parts of the Uncompahgre Plateau, causing the river to cut down deeper into the volcanic rocks, eventually reaching the harder Precambrian rocks below. At this point, many side-canyon rivers feeding into the Gunnison dried up, finding easier courses elsewhere, but the Gunnison River was trapped in its already deep gorge. Higher water levels during the last ice age are estimated to have carved the canyon at a geologically speedy rate of an inch every century, producing the canyon we see today in just a few million years.
As it thrashes its way through the canyon, the river drops an abrupt average of thirty-four feet per mile: the fifth-steepest river descent in North America. The Colorado River, in comparison, drops an average of seven and a half feet per mile through the Grand Canyon, considered one of the wildest white-water rides anywhere. In some places, the Black Canyon is only forty feet across, as it plunges more than 2000 feet into the bedrock.
The Gunnison River flows through a series of three manmade reservoirs (large, lake-like areas in the lower right of this image) before plunging into the depths of the Black Canyon.
It’s possible to spot the Black Canyon of the Gunnison on flights to Montrose, Grand Junction, or Colorado Springs, Colorado.
