The most common rocks found throughout the park are metamorphosed sedimentary rocks of late Precambrian age. These rocks are collectively grouped together in the Ocoee Supergroup and are from 1 billion to 500 million years old. The rocks of the supergroup consist of highly metamorphosed phyllites, schists, and quartzite to less metamorphosed slates, shales, sandstones, and metasiltstones. The supergroup is divided into three groups: the Snowbird, Great Smoky, and Walden Creek. The most abundant formations in the park are the Thunderhead Sandstone and the Anakeesta Formation (composed of slate, phyllite, and schist). These two formations make up many of the resistant layers over which waterfalls cascade (like Laurel Falls above) and make up the bulk of the crest of the mountains.
The last types of rocks found in the park are the sedimentary rocks that range from 500 to 300 million years old (Paleozoic Era). These rocks are mostly limestones, dolostones, shales, and sandstones that are characteristic of rocks found in the Ridge and Valley province located west of the park. Exposure of these rocks is limited in the park, and can only be seen through "windows" through the older (and topographically higher) bedrock. These are called coves and are areas where weathering has cut through the older Precambrian rock to expose the Paleozoic rocks located beneath the Great Smoky thrust fault. One such cove is Cades Cove, and the soils made by the weathering of the limestone made the coves attractive for early settlers who made their homes in the coves.
The characteristic shape and diverse flora and fauna that make up the park are the result of over 200 million years of erosion that has taken place since the Appalachian orogeny. The most dramatic changes have taken place in the last 1.8 million years during the Quaternary Period. During this time the earth has cycled through a series of glacial and inter-glacial epochs. While there is no evidence of Great Smoky Mountain National Park having ever had glaciers, the existence of large ice sheets did alter the climate in the park, allowing for more northern species to find an agreeable place in which to flourish. As the last ice sheet retreated 10,000 years ago the plants and animals migrated higher up the mountains until today five different forest zones exist within the park. Without the ice age, the diversity of trees and animals would not be seen in the park.
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