Geologic units in Williamsburg county, South Carolina

Penholoway Formation (Pleistocene) at surface, covers 45 % 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.

Waccamaw Formation (Pleistocene) at surface, covers 31 % of this area

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

Socastee Formation (Pleistocene) at surface, covers 9 % of this area

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

Alluvial Valley Swamp (Quaternary) at surface, covers 7 % 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.

Tidal Marsh (Quaternary) at surface, covers 6 % of this area

Peat and muck deposits along tidal margins of esturaries and back bays. Deposits range from a few feet to 60+ feet deep. Locally include silt and fine sand and clay as levees on tidal channels. At depth peaty material may be accumulated from fresh water plants. Peat at the surface dominated by spartina and other salt tolerant species.

Chenier plain and deltas of Suwannee & Chattahoochie Rivers (Holocene) at surface, covers 0.9 % of this area

Chenier plain and deltas of Suwannee & Chattahoochie Rivers