Qa
Alluvium (Holocene)
QTt
Terrace deposits, upper level (Pleistocene and Tertiary)
Qd
Debris (Holocene and Pleistocene)
Qt
Terrace deposit, low level (Holocene and Pleistocene)
Tt
Terrace deposits (Tertiary)
Kps
Potomac Formation (Lower Cretaceous) Sand-dominated lithofacies
Ttu
Highest level upland terrace deposits (Tertiary)
Qc
Colluvium (Holocene and Pleistocene)
Kpc
Potomac Formation (Lower Cretaceous) Clay-dominated lithofacies