Geology on the edge

The ancient Appalachian Mountains may have been the largest range in the history of the planet, a massive upthrust system created over 200 million years ago by the collision of two tectonic plates.  As with all geology, though, what goes up indeed comes down.  Millions of  years of erosion by water, ice and wind reduced this great system of mountains to the rolling ridges we see today, literally the roots of what used to be.

So where did all that rock go?  Look around the states of the mid-west, central south and eastern Great Plains.  Much of that area was under water millions of years ago but that primordial sea was gradually filled in during the Pennsylvanian Age by all the material eroded from the eastern mountains, raising the surface altitude hundreds of feet and resulting in a plateau that gradually dried and compacted under its own weight to create a thick layer known as Corbin Sandstone.

Plate action was not through with the area, though, as more uplifting resulted in the Cumberland Plateau, essentially the foothills of the ancient Appalachians.  As climate change dropped more and more water on the western slopes of the mountains all that water flowed westward, carving away at the Plateau’s sedimentary foundation.  Vertical fracturing along the edge of the Plateau gave the water more channels to exploit, allowing it to carve away the flatlands and create the rolling ridges of the Pottsville Escarpment found in eastern Kentucky.

One stream was more productive, though, cutting deeper than most and creating the Red River Gorge area east of Lexington, KY.  The Gorge is near the edge of the Escarpment – driving west toward Lexington you quickly leave the rolling ridges and enter the flatter, grassy horse country Kentucky is so famous for.

The different strata found in the Gorge vary in their ability to resist erosion, with the harder layers mostly found at the top of the ridges, the remains of the original Plateau.  Undercutting by water and ice wears away the softer layers underneath, resulting in overhangs, arches and bridges.  The Gorge area has over 100 of these features, rewarding the hiker with a variety of geological sights along most any trail.

Unlike the western arches and bridges standing alone in their deserts, the Gorge’s formations are surrounded by a deciduous forest, making it difficult to back up and get the whole scene without a very wide angle lens.  My first reaction was “why don’t they cut down some of these trees…” but I read later that had been done already.  The whole region was clear cut in the late 1800’s/early 1900’s to supply wood for the rapidly growing country.  All of the area is second or third growth and pretty thick in some places.  On reflection I realized I’d rather have the trees and just work around them for my photography.  Besides, my reason for being there was to catch the fall colors, not the geology!