English: This is an oblique aerial view of the Appalachians in eastern America. The Appalachians extend from Quebec to Alabama, go underground in the Mississippi River area, and re-emerge in the Arkansas-Oklahoma-Texas area as the Ouachita Mountains. The overall mountain chain formed as a result of three separate tectonic collision events during the Paleozoic. The earliest was the Taconic Orogeny (Late Ordovician to Early Silurian) - a volcanic island arc collided with what is now the New England area. Next was the Acadian Orogeny (Late Silurian to Devonian) - a microcontinent called Avalonia collided with eastern North America. The third and most significant mountain building event was the Allegheny Orogeny (Pennsylvanian) - Africa collided with eastern North America. This was a Pangaea supercontinent formation event.

The Appalachians mostly lack the sharp-peaked mountains common to western America's Cordillera, the Andes of South America, the Alps of Europe, or the Himalayas of Asia. Compared with those geologically young mountain chains, the Appalachians are relatively old - they have been subjected to long-term erosion for about one-third of a billion years.

The Appalachian Mountains consist of three physiographic provinces. From west to east, they are: 1) the Valley & Ridge; 2) the Blue Ridge; and 3) the Piedmont.

This photo shows the near-western margin of the Blue Ridge in the Shady Valley area of the northeastern tip of Tennessee. To the west is the Valley and Ridge, which consists of folded sedimentary rocks of Paleozoic age that have been eroded into long, sublinear ridges separated by ~flat-floored valleys. The Blue Ridge province is mostly composed of Precambrian-aged basement rocks (igneous & metamorphics). The mountains of the Blue Ridge are generally rounded and not very tall.

At this site, the western Blue Ridge actually has broadly folded Lower Paleozoic sedimentary rocks. The green-floored valley at lower left is Shady Valley. It is along the axis of the Stony Creek Syncline, a broad, downarched fold cored by Cambrian-aged dolostones of the Shady Dolomite.

The dark, forest-covered area is the Iron Mountains, which consists of Cambrian-aged sedimentary rocks of the Chilhowee Group.

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See info. at:

en.wikipedia.org/wiki/Appalachian_Mountains