The roof of the Smokies owes its character to time. Erosion is a great equalizer, one that can humble and beat down a landscape. Before wind, rain, ice and snow seriously began gnawing away at the Appalachian Mountains, the range possibly towered to more than 27,000 feet (8,229.6 m) and claimed peaks that could honestly be viewed as such. Once upon a time this was a lofty, cloud-shredding range, one that today would make the Rocky Mountains blush with envy.

Evolution of the Southern Appalachian Mountains from Precambrian to Pennsylvanian, Great Smoky Mountains National Park / DeWindt (1975) via NPS Geologic Resources Evaluation Report 2008

It was an incredible collision that pushed the Smokies skyward above the Eastern Seaboard roughly 300 million years ago during the Paleozoic Age. Responsible for the uplifting were Europe, Africa and South America, which collided with North America in a tectonic plate shift that created the super continent known as Pangea. That continental collision produced not just the Smokies, but the entire Appalachian Range that runs north through the Blue Ridge Parkway, Shenandoah National Park, and on up to Acadia National Park in Maine. This collision pushed some of the oldest metamorphic rocks of North America – the so-called Precambrian basement -- up over a much younger sedimentary and volcanic layer later laid down.

At the height of mountain building the Appalachians boasted sharp, alp-like angular crags and rocky slopes upon which vegetation struggled to take root in. But as the muscular range began to lose its physique and develop a paunch -- not unlike most others in mid-life -- the evolving vegetation gained a decided and tenacious edge. Peaks were sawn down, rounded, covered with shrubs, bushes, trees and brambles.

Drainages that creased their flanks quickly became fertile corridors as leaves fell to the ground and went on to rot in the moist setting. As they quickly decomposed, the organic matter provided the key ingredient for the rich, loamy soil that today not just supports but nourishes the ecosystem and its forests and their 100 native tree species and more than that number when you get around to counting shrubs. As continued erosion removed the geologic overburden, the underlying rocks were cracked open, many of their vertical joints still showing today.