

The Appalachian Mountains began forming approximately 1.5 billion years ago. About the same time that sea animals were first evolving bones. The carbon that became the coal under them was deposited approximately 300 million years ago when they formed the central continental divide of the Pangea supercontinent. That was when they were at their highest, estimated to have been about the same height as the modern Alps.
https://youtube.com/watch?v=X5iaZf21R8w