Mountain Time: Rock of Ages

Mountain Time: Rock of Ages

Butch McDade

Story and images by Arthur "Butch" McDade

The Appalachian Mountains are ancient highlands formed millions of years ago. They’ve been shaped, contorted, and warped by great forces since time immemorial. Writer John McPhee describes the Appalachian range as “a compressed, chaotic, ropy enigma, four thousand kilometers from end to apparent end, full of overturned strata and recycled rock, of steep faults and horizontal thrust sheets, of folds so tight that what had once stretched 20 miles might now fit into five.” And included in this chaotic mix are the Great Smoky Mountains, highlands that writer Horace Kephart called “the roof-top of Eastern America.”

Coarse Thunderhead Sandstone at Forney Ridge
Coarse Thunderhead Sandstone at Forney Ridge

Geologists say Earth’s crust is broken into continental, crustal plates which move very slowly over the upper reaches of the planet’s mantle. This process is sometimes called “continental drift” by the popular press. When these plates collide, mountains can form. During one such mountain-building period called the Alleghenian orogeny, ancestral continental plates—which included today’s North America and Africa—slowly collided into each over, causing great masses of sediments to be thrust up, forming high mountains that included today’s Smokies. When the continental plates ultimately drifted apart over time, erosion relentlessly attacked the mountains, reducing them from towering alpine domains to the rolling green ridgelines we see today.

Geologists call the predominant rocks of the Smokies the Ocoee Supergroup. In this supergroup is a component called the Great Smoky Group, rocks that were lightly metamorphosed during the heat and pressure of mountain-building. Thunderhead Sandstone, Elkmont Sandstone, and Anakeesta Formation are in this group, forming the main mass of the Smokies. You can get fine views into the “red-heart” of this geologic group from the overlooks and observation towers in the Smokies as you gaze into the surrounding sea of endless peaks. 

Rolling hills

Today, the Smokies don't resemble the high, jagged Rockies or Sierra Nevadas. The Smokies are overlain with a lush cover of plants, a result of being in a temperate zone with 40-80 inches of annual precipitation.

When viewing the Smokies today, it's sometimes hard to see the rocks for the trees. Rose Houk, in her book Great Smoky Mountains National Park, quotes Smokies’ geologist Philip King as saying, “Only now and then, when the visitor’s trail through the forest must circuit a rough ledge or rock, can he realize that the forest and the soil on which it grows are a mere veneer—a thin cover over the ancient rocks of the Smoky Mountains.”

The Smokies are “elder statesmen” of American mountains. They’ve been whittled down from their former majestic heights, but they’re iconic highlands, home to a fascinating botanical and biological diversity. Their significance was understood way back in the mid-19th century when pioneering geographer Arnold Guyot, who measured and documented part of the Smokies range, described them as “the master chain of the Appalachian System.”

Arthur “Butch” McDade retired as a park ranger from Great Smoky Mountains National Park. He is the author of Old Smoky Mountain Days, The Natural Arches of the Big South Fork, and is a contributing writer to The Encyclopedia of Appalachia.

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