What lies buried 20,000 feet under the Appalachian Mountains?

Followup video at What formed this ancient, 24,000 foot...

The structure of the Appalachian Mountains intrigued geologists for more than a century, particularly because so much of the US population live so close to these mountains. During the 1970s and 1980s, geologists became particulary interested in what is underneath the Appalachian Blue Ridge, where rocks that formed deep in the Earth, such as granite and gneiss, are found at the Earth's surface. This video illustrates how geologists interpret the deep structure of a part of the Appalachians, how geologists gained this information, and what the information can contribute to learning about climate change. Microsoft Paint diagram drawing and a physical "sandbox" model are included.