The Appalachian Mtns. resulted from three separate orogenies (mountain-building events) involving the North American continent. The first and second, or Taconic and Acadian orogenies, resulted from collision with volcanic island arcs. The final collision - or Alleghenian orogeny (320-250 MYA) - involved North America and African. All of these orogenies sutured together the supercontinent Pangaea.
(MYA = Million Years ago)

Whereas the Highlands Province represents part of the "Crystalline Appalachians," (a region underlain by ancient metamorphic and igneous rocks), the region to the north and west of the Highlands is underlain by flat-lying to steeply folded and faulted Paleozoic sedimentary rocks.

An imposing escarpment, known as the Allegheny Front, divides the Ridge and Valley Province from the Appalachian Plateau Province.

At one time, the Appalachians probably rivaled the height of the Alps in Europe.