Geologic Overview of the Cheat River Gorge

The Cheat River Gorge from the main overlook at Coopers Rock State Forest, West Virginia. Photographed 11/01/2010.

The Cheat River Gorge is a remarkable natural feature located in northeastern West Virginia.  This area is known for beautiful scenery, white-water rafting and rock climbing, all thanks to the geologic processes that have forged this wonder.

From the Cambrian through the Mississippian Periods (about 542 to 318 million years ago), several mountain building events known as orogenies had uplifted much of the land in northeastern North America.  These orogenies were the result of tectonic forces pressing various continental and oceanic plates together over tens of millions of years. As the plates collided, much of the land was forced upward, resulting in the formation of the earliest parts of the Appalachian Mountains.  Changing elevations and sea levels lead to many different depositional environments in this area over those hundreds of millions of years.

During the Mississippian Period (about 359 to 318 million years ago) much of what is now West Virginia was just off the west coast of these emerging mountains.  This warm, shallow inland sea harbored an abundance of shelled marine invertebrates.  As these animals died, their shell material accumulated on the sea floor.  Over time this material was compacted into limestone, in this case forming the massive Greenbrier Limestone.

During the Pennsylvanian Period (about 300 to 318 million years ago) much of what is now West Virginia was low-lying and coastal.  As the early Appalachians rose higher from orogenies, the sea retreated from West Virginia.  Located between the early Appalachians to the east and the retreating shallow inland sea to the west, this area accumulated a variety of sediments. The area would have harbored beaches, swamps , river channels, and deltas.  It was during this time that the Pottsville Group was formed, containing mostly sandstone and conglomerate but also some shale and coal.

Ripple marks in Pottsville sandstone, formed from water moving over sand. Photographed 11/01/2010 at Coopers Rock State Forest, West Virginia. Quarter for scale.

But there was still one more orogeny to affect this region.  Late in the Pennsylvanian Period the African continent collided with North America.  Known as the Alleghenian Orogeny, this was the most significant mountain-building event that finished forming the Appalachians.  The previously deposited sedimentary rocks, including the Greenbrier Limestone and Pottsville Group, were compressed, folded, and elevated over tens of millions of years.

Simplified diagram of compression and folding of sedimentary bedding.

Although sandstones like those found in the Pottsville Group are very resistant to weathering, the folding of the beds fractured and weakened them.  This particular area is home to the Chestnut Ridge anticline, where beds are folded upward and fractured.  In much more recent time, the geologically young Cheat River managed to wear through the damaged sandstone beds capping these sedimentary rocks.

Resistant Pottsville Sandstone near the top of the Cheat River Gorge. Photographed 11/01/2010 at Coopers Rock State Forest, West Virginia.

Once worn down to the less resistant Greenbrier Limestone, the river accelerated its downcutting.  The result today has been the Cheat River Gorge:  a testament to the power of running water to wear through solid rock.

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About Jeremy Sell

Science and nature nerd.
This entry was posted in Geology, Paleoecology and tagged , . Bookmark the permalink.

One Response to Geologic Overview of the Cheat River Gorge

  1. Pingback: Dr. Ferber’s Water Journal – Day 49: Celebrating Nineteen Years | The King's Green Pad

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