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Mineral Resources > Online Spatial Data > Geology > by state > South Carolina Geology

Geologic units in Williamsburg county, South Carolina

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

Lithology: unconsolidated deposit

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

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

Lithology: sand; limestone

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

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

Lithology: sand; clay or mud

Alluvial Valley Swamp (Quaternary) at surface, covers 7 % of this area

Alluvial Valley Swamp: 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.

Lithology: sand; gravel; silt; peat

Penholoway Formation (Pleistocene) at surface, covers 45 % of this area

Penholoway Formation: 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.

Lithology: sand; clay or mud

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

Tidal Marsh: 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.

Lithology: peat; silt; sand; clay or mud