Rock reading.

June 11, 2012 § Leave a comment

“Rocks are records of events that took place at the time they formed. They are books. They have a different vocabulary, a different alphabet, but you learn how to read them.” – John McPhee

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Black Canyon of the Gunnison, Montrose County

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“With their four-dimensional minds, and in their interdisciplinary ultra verbal way, geologists can wiggle out of almost anything.” – John McPhee

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Large bands of Pegmatite Ribbons on the Painted Wall of the Black Canyon

One of the most magnificent aspects of The Black Canyon of the Gunnison is its exposure of Precambrian rocks dating over 1.7 billion years old — one of the best in the world. These ancient rocks, also called basement rocks, are composed of gneiss, schist, and granite, as well as diorites, pegmatites, and gabbros (Thornberry-Ehrlich, 2005).

These metamorphosed sedimentary and igneous rocks underwent intense heat and pressure, which folded them within the earth — creating an alternating pattern of gneiss and schist.

In addition, ribbons of intrusive pegmatite are interspersed, which formed as hot magma forced its way into the rock and cooled very slowly, forming large crystalline structures.

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“Are these the end times?  Yes. And they have been this way since the beginning. Welcome to planet Earth, a wonderful but not entirely stable place to live.” – Craig Childs

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A mysterious feature of the Canyon is that the entire Paleozoic era is missing from the rock record shown by Precambrian rocks overlain with Mesozoic rocks.

Resembling more of a cut in the earth than a wide, river formed canyon, the Black Canyon of the Gunnison is an example of the diverse geology in southwestern Colorado. At the bottom of the canyon, the Gunnison River continues its journey, flowing as it has for the past millions of years.

Part of the Black Canyon has now been designated a National Park. The area’s status changed from National Monument to National Park in 1999, making it the newest National Park in the United States.

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Colorado looking from the east

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“Civilization exists by geological consent, subject to change without notice.”
-Will Durant

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Colorado Geological Survey Map

Although seven physiographic provinces are defined in Colorado, there are basically three topographic/geologic zones in the state. Topographically, the state is divided into Eastern Plains, Rocky Mountains, and Colorado Plateau. Geologically, the eastern plains and western plateau are composed of sedimentary rock whereas, the Rocky Mountain province is a complex assortment of igneous, metamorphic, and sedimentary rocks in approximate equal proportions.


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“We learn geology the morning after the earthquake.”- Ralph Waldo Emerson

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Black Canyon Contorted gneiss

Black Canyon of the Gunnison National Park, Colorado. Contorted gneiss on the north rim of Black Canyon near Colorado State Highway 92. The contortions were caused by flowage under great heat and pressure in the depths of the earth’s crust. Complicated structures such as these are confined to the Precambrian rocks. Light-colored bands are mostly feldspar and quartz; dark bands are mostly quartz and biotite.,%20W.R.%20123&SIZE=medium

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“The geologist takes up the history of the earth at the point where the archaeologist leaves it, and carries it further back into remote antiquity.” – Bal Gangadhar

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Black Canyon of the Gunnison CO

The 53-mile long narrow gorge along the Gunnison River is known as the Black Canyon of the Gunnison. Its spectacular landscape is a feast for the eyes. Formed by the slow action of water and rock scrubbing down the hard Proterozoic rock, the sheer black walls of the canyon plunge to nearly 2,700 feet into the narrow gorge.

There are many activities available including hiking the rim of the Canyon, fishing for the large trout that make the Gunnison River their home, raft or kayak the whitewater section of the River, and/or camp along the Canyon Rim.

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39th Parallel Black Canyon of the Gunnison

A canyon that in many places is deeper than it is wide. It defies belief.

The Painted Wall is the highest unbroken cliff in Colorado with a drop of more than 2,000 feet. The gneiss and schist exposures are dark, while the pegmatite dikes are lighter in color. The rocks record a complex story of continent-terrane collisions, intrusions and mountain-building episodes. The rocks on the rim preserve a relatively flat surface representing a profound amount of erosion…many vertical miles of rock are missing, having been converted into an unimaginable mix of pebbles, sand and mud distributed by rivers that long ago ceased to exist.

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39th paralel Black Canyon of the Gunnison 2

The very existence of the canyon is a handy mystery. It carves through what is essentially the top of a mountain ridge, and looking at maps, it looks like the river should be flowing someplace else. One has to drive a long way uphill to reach the south rim. The canyon is an example of a superimposed drainage, one whose pathway was established by external factors (lava flows from adjacent mountains) until it was trapped into flowing across a place that seems to make no sense.

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39th parallel BLACK CANYON

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