Geologic units in Marion county, South Carolina

Alluvial Valley Swamp (Quaternary) at surface, covers 29 % of this area

Unconformable on all underlying units, fluvial sand and gravel at base, grading upwards into fine sands and silts, local peat. May be overrun with recent sediments from forest cutting and agriculture.

Bear Bluff Formation (Pliocene) at surface, covers 27 % of this area

One of the older coastal terrace sequences in the Carolinas. Equivalent to Windsor Fm.

Penholoway Formation (Pleistocene) at surface, covers 20 % of this area

Similar to Cape May, broad lateral extent underlying terraces in the Carolinas; swamps and ridges on terrace surface were originally barrier islands and back bays. Superimposed on these landforms are swarms of Carolina bays.

Socastee Formation (Pleistocene) at surface, covers 16 % of this area

Low coastal formation in Carolinas like Penholoway but younger and lower in altitude.

Waccamaw Formation (Pleistocene) at surface, covers 8 % of this area

Another Carolina costalized terrace of early-middle Pleistocene age. Deeply weathered.