Geology

The regional structure of the underlying rock strata dips gently to the west in a layer cake fashion with younger rock layers overlying older ones. These rocks are deposits from the Mississippian Period, dating from 360 to 320 million years ago. The dominant rock type of this sequence is the Greenbrier limestone which was created when the area was covered by an inland sea and the environment was similar to what is found in the Bahamas today.

The rocks occurring below and above this limestone are the lithified sediments from erosion of the ancestral Appalachian mountains far to the east. They are composed primarily of shales and sandstones. Due to the westward dip and the general westward trend to the river, the age of the rocks exposed along the river bottom and bank gets progressively younger as you follow the river downstream.

Like the New River it later joins, there is evidence that the Lower Greenbrier River is very ancient. Below Ronceverte, the river leaves the early Mississippian red shales and traverses the Greenbrier limestone. This massive 900' thick layer of soluble rock is characterized by numerous caves, sinkholes, and underground streams. On the North bank of the river, just below the village of Fort Spring, there is a large spring which is the emergence of a pirated surface stream. This spring is the subterranean runoff from the area around Lewisburg. Also in this area are abandoned "ox-bow" river channels and high river terraces. Just before the river reaches the town of Alderson, it passes through a substantial water gap cut between Muddy Creek Mountain and Mt. Pleasant. These structures date back 40 million years or more as regional uplift accelerated the downward cutting of the river and its tributaries.

Between Alderson and Talcott, the river meanders through the shale sequences that overlie the western dipping of limestone. The relatively easy weathering of this less resistant rock results in broad floodplains that flank both sides of the river. The last 3.5 miles of the river valleys become steep-walled as the river cuts through the younger interbedded and relatively weather-resistant sandstones of late Mississippian age.

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