Physiographic Provinces of West Virginia

Dividing Line

Map of Physiographic Provinces of West Virginia

Physiographic Provinces of West Virginia

Most of West Virginia is a dissected, westward-tilting plateau called the Appalachian Plateau Province. In the northeast part of this province, a subprovince called the Allegheny Mountain Section combines elements of the folded mountains to the east and the dissected plateau. The eastern boundary of the Appalachian Plateau, the Allegheny Front, is a prominent geological feature which runs northeast-southwest across the State. East of the Allegheny Front are a series of long folded mountains and valleys defining the Valley and Ridge Province. East of the main group of folded mountains and valleys is the Great Valley subprovince. Along the eastern State boundary in Jefferson County is the Blue Ridge Province.

Bedrock Geology of West Virginia

Most of the rocks in West Virginia are sedimentary, deposited during the Paleozoic Era (600 to 230 million years ago); very few igneous or metamorphic rocks occur in the State. The geologic history of West Virginia prior to one billion years ago is poorly understood. The oldest exposed rock in the State is the Catoctin Greenstone, a metamorphosed lava deposited 800 million years ago. Later, a marine sea covered most of West Virginia and deposited marine limestones, shales, siltstones, and sandstones during the Cambrian and Ordovician periods.

Movements of the earth's tectonic plates cause episodes of mountain building which, with subsequent erosion and production of sediments, can have major effects of the geologic history of an area. The first of these mountain-building episodes to affect West Virginia, the Taconic Orogeny, formed mountains to the east of the State that were a source of sediments during the Ordovician, Silurian, and early Devonian periods. Clastics and carbonates were deposited with clastics predominating in the eastern part of the State. Also, non-marine deposition took place and evaporites were deposited in the northern part of West Virginia in the late Silurian.

Highlands to the northeast, formed in the Acadian Orogeny, were the source of clastic sediments in the Middle and Late Devonian. The sea regressed to the west at the end of the Devonian, and continental red beds were deposited over most of the State. The sea covered West Virginia again in the Middle Mississippian (about 330 million years ago). During this time, the Greenbrier Group, composed mainly of limestone, was deposited.

The sea retreated again near the end of the Mississippian, and during the Pennsylvanian, West Virginia was low-lying and swampy. During this period, thousands of feet of non-marine sandstone, shale, and coal were deposited.

During the Permian Period, the Appalachian Orogeny began, which was the dominant geologic event in the formation of the Appalachian Mountains. Much folding and thrust-faulting occurred, especially in the eastern part of the State. Erosion became the predominant geological processes.

No sedimentary rocks from the Mesozoic Era (230 to 70 million years ago) exist in West Virginia. However, hundreds of igneous dikes from this time are found in Pendleton County.

The glaciers of the ice ages never reached West Virginia. A large lake caused by an ice dam to the north resulted in lake deposits in the northern part of the State and drainage changes and alluvial deposits in the southern part. These are the only Cenozoic Era (younger than 70 million years ago) deposits in West Virginia.

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