Geology of the Waterford quadrangle, Virginia and Maryland, and the Virginia part of the Point of Rocks quadrangle

The bedrock geology of the Waterford quadrangle and of the Virginia part of the Point of Rocks quadrangle consists of a portion of the Middle Proterozoic basement core and its cover sequence on the eastern limb of the Blue Ridge anticlinorium and the adjacent early Mesozoic Culpeper basin. The three major rock associations in this area are: 1) Middle Proterozoic gneisses intruded by late Proterozoic metadiabase dikes, 2) unconformably overlying late Proterozoic and early Paleozoic metavolcanic and metasedimentary rocks, and 3) Upper Triassic sedimentary strata intruded by early Jurassic diabase. The Triassic and Jurassic rocks are separated from the older rocks by a major normal fault, the Bull Run fault. Late Cenozoic surficial deposits of three major types unconformably overlie the bedrock: colluvium derived from Catoctin Mountain, terrace deposits of the Potomac River, and flood plain alluvium of the Potomac River and its tributaries. -from Authors