Geologic units in Colleton county, South Carolina

Bear Bluff Formation (Pliocene) at surface, covers 30 % of this area

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

Chenier plain and deltas of Suwannee & Chattahoochie Rivers (Holocene) at surface, covers 14 % of this area

Chenier plain and deltas of Suwannee & Chattahoochie Rivers

Alluvial Valley Swamp (Quaternary) at surface, covers 11 % 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.

Duplin Formation (Pliocene) at surface, covers 11 % of this area

Coastal terrace of Carolinas. Pliocene equivalent to Yorktown. Deeply weathered.

Tidal Marsh (Quaternary) at surface, covers 9 % 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.

Swamp (Quaternary) at surface, covers 8 % of this area

Extensive cypress swamps occur in low-lying poorly-drained bay deposits. Limit of cypress is southern Delaware; from NJ south to Georgia. Atlantic white cedar is original species. Commonly extensive thick peat and buried wood.

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

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

Socastee Formation (Pleistocene) at surface, covers 5 % of this area

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

Penholoway Formation (Pleistocene) at surface, covers 5 % 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.

Beach (Holocene) at surface, covers < 0.1 % of this area

Holocene beach complex sediments. Sands and gravels of littoral zone, dune system, barrier system.