View from the slopes of Back Allegheny Mountain, looking east, in the Appalachian Mountains, North America. Visible are Allegheny Mountain (in the Monongahela National Forest of West Virginia, middle distance) and Shenandoah Mountain (in the George Washington National Forest of Virginia, far distance).
|Elevation||6,684 ft (2,037 m)|
|Length||1,500 mi (2,400 km)|
|Countries||United States and Canada|
|State/Province||Newfoundland and Labrador, Saint Pierre and Miquelon, Quebec, Nova Scotia, New Brunswick, Maine, New Hampshire, Vermont, Massachusetts, Connecticut, New York, Pennsylvania, Maryland, Virginia, West Virginia, Ohio, Kentucky, Tennessee, New Jersey, North Carolina, South Carolina, Georgia, and Alabama|
|Orogeny||Taconic, Acadian, Alleghanian|
The Appalachian Mountains (i/ˌæpəˈleɪʃɨn/ or /ˌæpəˈlætʃɨn/,[note 1] French: les Appalaches), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period and once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded. The Appalachian chain is a barrier to east-west travel as it forms a series of alternating ridgelines and valleys oriented in opposition to any road running east-west.
Definitions vary on the precise boundaries of the Appalachians. The United States Geological Survey (USGS) defines the Appalachian Highlands physiographic division as consisting of thirteen provinces: the Atlantic Coast Uplands, Eastern Newfoundland Atlantic, Maritime Acadian Highlands, Maritime Plain, Notre Dame and Mégantic Mountains, Western Newfoundland Mountains, Piedmont, Blue Ridge, Valley and Ridge, Saint Lawrence Valley, Appalachian Plateaus, New England province, and the Adirondack provinces. A common variant definition does not include the Adirondack Mountains, which geologically belong to the Grenville Orogeny and have a different geological history from the rest of the Appalachians.