The Culpeper Basin in northern Virginia extends from just south of the Albemarle-County—Orange County line northeastward to the Potomac River, a distance of more than 148 km (90 mi). The basin continues northward across the Potomac and terminates just southwest of Frederick, Maryland. It occupies the western part of the Piedmont province. On the west it is bounded by an east-dipping normal fault; the sedimentary and volcanic strata dip westward into the fault (Fig. 1). The rocks in this area traditionally have been considered part of the Newark Group and referred to as Triassic, but Cornet's (1977) palynological study indicates that they range from Upper Triassic to Lower Jurassic.
The Culpeper Basin is one of the many basins in North America in which sedimentation extended from Late Triassic to Early Jurassic time (Cornet, 1977). Other such basins include the Newark in New Jersey, the Gettysburg in Pennsylvania, the Hartford in Connecticut, the Deerfield in Massachusetts, and the Fundy in Nova Scotia. The southernmost basins contain only Upper Triassic rocks. They include the Durham, Sanford, Wadesboro, and Dan River Basins in North Carolina and the Danville and Richmond Basins in southern Virginia (Cornet, 1977).