Geology of the Front Royal Quadrangle, Virginia

Rader, Eugene; Biggs, Thomas

This report provides a description of the geology of the Front Royal quadrangle, an area including Shenandoah National Park. Included in the report are discussions of stratigraphy, geologic structure, hydrogeology, and environmental geology of the area. The Front Royal 7.5-minute quadrangle is located in Warren County, northern Virginia. The area is mostly in the Valley and Ridge physiographic province but approximately 20 percent is in the Blue Ridge province. The bedrock ranges in age from Precambrian (Pedlar Formation) through Middle Ordovician (Martinsburg Formation). The Precambrian and Paleozoic rocks are assigned to 15 formations and 20 mappable units. Additionally, Cenozoic sediments consisting of terrace deposits, colluvium, and alluvium are mapped. The major structural features consist of the southeastern limb of the Massanutten synclinorium and an overthrust salient of the Blue Ridge anticlinorium. The present attitude of the bedrock is the result of at least two tectonic events from the east which produced oversteepened and locally overturned east limbs of synclines and west limbs of anticlines. The major faults have an easterly dip, with both high- and low-angle faults present. The major fold axes of the area trend to the northeast along the general strike of the formational outcrops. Well-developed cleavage, commonly exhibiting two generations of deformation, and joints are exposed at many localities. Impure limestone and crushed and broken stone are produced. Iron, manganese, and copper ores have been mined in the past. Limestone, dolomite, sandstone, and shale are available as raw materials for many purposes. The five clastic sedimentary formations are consistent producers of small to moderate yields of water from intermediate depths, the eight carbonate formations have a wide range of water-well depths and yields, and the two igneous formations commonly yield only small quantities of water at relatively shallow depths. Data for land-use decisions is provided by environmental geology information obtained from geological characteristics such as lithology, slope stability, erodibility, rockfall areas, sinkholes, and cave areas. Reference to soils and land-use potential is made.