The Appalachian Mountains formed mostly during the Acadian Orogeny, in the Devonian period. Since their formation, the Appalachians have been greatly eroded. What we see today are simply the remnants of what was once a great mass. They are made mostly of sedimentary rock. The Appalachians are rich in coal, and also contain iron, petroleum, and natural gas.

In an event called the Alleghanian Orogeny, the oceanic crust was subducted beneath the continent that would someday be called North America. This made the continent that would be called Africa drift closer to North America. The continents continued to drift, until they collided. This massive collision caused the land to fold upward, creating the Appalachian Mountains. This collision, and a couple of smaller ones led to the formation of Pangea, an early supercontinent.

This is the beginning of the process called the Alleghanian Orogeny, that caused the formation of the Appalachian Mountains.