The Appalachian Ridge and Great Appalachian Valley are geologic formations created between 300 and 400 million years ago. In multiple collisions, the tectonic plates containing North America and Africa came together in the formation of the Pangaea supercontinent. These collisions made multiple ridges at the edges of these continents, forming the Appalachian Mountains.
Bounded by the steep Blue Ridge on the east and the coal-rich Appalachian Ridge on the west, the Great Appalachian Valley is a series of valleys formed from the same ridge-building events that created the Appalachian Mountains. It includes areas like the Shenandoah Valley, Cumberland Gap and Hudson River Valley. These valleys, easy for humans and animals to traverse, have been used as travel and hunting routes since prehistoric times.
About 470 million years ago, the Taconic ridge-building event began the Appalachian mountain-building series when the small continent Baltica collided with North America. This was followed by the Acadian event 380 million years ago and finally by the Alleghanian event, both of which involved the African proto-continent.
Geologically, these areas are very distinct. The northern Appalachians and the African side of the Appalachians are known as the Crystalline Appalachians due to the large quantity of crystalline igneous and metamorphic rock found in these regions, remnants of the ancient continents that formed them. The west side of the Appalachians is composed of sedimentary rock rich in coal and fossil fuels formed when that region was an ancient shallow ocean.