Saturday, June 22, 2013

Geoformation of the Black Canyon of the Gunnison

Black Canyon: so named on account of its steep and narrow body which makes it difficult for sunlight to penetrate to the very bowels of this magnificent 48-mile long geologic structure. The resulting shadows make the rocky walls appear pitch black and you often can't see the bottom. With an average drop of 34 feet per mile, the ancient Gunnison carves through the tough 1.7 billion year old Precambrian gneiss at a dismal <1-inch every 100 years.

Black Canyon of the Gunnison
What was that? You asked if the Precambrian gneiss is so tough to erode, why didn't the Gunnison River find softer rock to carve? I mean, that is the basic concept of watershed hydrology; water goes where it is resisted the least. Well, you see, the mighty Gunnison River, which is 15 million years old itself, was trapped.

Sit back, relax, have some wine (a lot of wine?) and let me tell you an 'old as stone' story about how the historic Black Canyon was created... 

Canyon Formation
Between 40 and 70 million years ago, 1.7 billion year old Precambrian metamorphic gneiss that formed during the Precambrian era went through a massive uplift (known as the Gunnison Uplift) during the Laramide orogeny. What is the Laramide orogeny you ask? Well, without getting into too much crazy plate tectonic and geology talk, it is what made the early version of the Rocky Mountains. After this massive upheaval of tough metamorphic rock... lots of volcanos went off. When I say lots, I mean a lot a lot. All of the West Elk Mountains, La Sal Mountains, Henry Mountains and Abajo Mountains contributed to burying the newly risen gneiss in several thousand feet of volcanic ash and debris.

Looking down into the beast
*Disclaimer... I should say I use the term "newly risen" loosely, since technically the volcanic eruptions happened more than 5 million years after the Gunnison Uplift.

Anyways... that's a lot of volcanic shit! Er... debris. If you don't know your geology, volcanic debris is soft in the way rocks go. In water erosion terms, it is easy carving. When the Gunnison River was formed 15 million years ago as a mere run-off from the La Sal and West Elk Mountains, it started carving through that 'soft' volcanic rock with ease.

After the Gunnison carved itself a nice canyon of least resistance, Mother Earth decided to literally shake things up a bit. Another uplift occurred roughly 2 to 3 million years ago and literally trapped the Gunnison in its present course. With no where to turn and no softer rock to escape through, the river started the slow erosion of the gneiss from the Gunnison Uplift at a rate of 1-inch every 100 years.

Vertical cliffs of Black Canyon
Present Day
The current Black Canyon of the Gunnison is one of the most spectacular sites one could see in Colorado, yet it is relatively under visited due to its remoteness. The river course is practically the same as it was 2 to 3 million years ago thanks to that tough metamorphic gneiss. The raging waters of the river are only a whisper from the rim. Since the river is now damed, the flow is much slower than the 12,000 cubic feet per second, 275 horse power it once was, causing an even slower erosion.

Some interesting tid-bits:
  • At its narrowest point, the black canyon is only 40 feet wide.
  • There is a 2-mile section of the canyon that drops 480 feet in elevation.
  • The Black Canyon drops more in elevation over its 48 miles than the entire 1,500 miles of the Mississippi River.
  • While the Black Canyon averages a drop of 34 feet per mile in elevation, the Grand Canyon only drops roughly 7.5 feet per mile

Oh... and it has some killer sunsets...


Black Canyon of the Gunnison National Park is located approximately 250 miles from Denver, CO, 15 miles east of Montrose, CO, and 60 miles west of Gunnison, CO.

Want to know more? Visit Black Canyon of the Gunnison National Park's website to learn about camping, rock climbing, fishing, wild life viewing and other opportunities.

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