Following the informal usage of Lee (1979, 1980), the Rapidan Member of the Manassas Sandstone is here named for exposures along the Rapidan River, Orange Co., Va. It consists of greenstone, cobble, pebble, and boulder conglomerate with minor sandstone, quartzite, and quartz clasts in a sand and silt matrix. It is exposed in the southern part of the Culpeper basin and in the Barboursville basin and is the basal unit of the Manassas in the drainage area of the Rapidan River. It unconformably overlies and is locally in fault contact with pre-Triassic crystalline rocks and is laterally and vertically gradational with the overlying Poolesville Member of the Manassas. Thickness ranges from 70 to 140 m (230 to 460 ft). Age is probably late Carnian based on palynoflora from the overlying Poolesville Member.

Source: GNU records (USGS DDS-6; Reston GNULEX).