Geologic units in Dillon county, South Carolina

Bear Bluff Formation (Pliocene) at surface, covers 51 % of this area

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

Duplin Formation (Pliocene) at surface, covers 22 % of this area

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

Alluvial Valley Swamp (Quaternary) at surface, covers 12 % 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.

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.

Socastee Formation (Pleistocene) at surface, covers 4 % of this area

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

Waccamaw Formation (Pleistocene) at surface, covers 4 % of this area

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

Black Creek Formation (Cretaceous) at surface, covers 1 % of this area

Clay, gray to black, lignitic; contains thin beds and laminae of fine-grained micaceous sand and thick lenses of cross-bedded sand. Glauconitic, fossiliferous clayey sand lenses in upper part.

Yorktown Formation and Duplin Formation, Undivided (Tertiary) at surface, covers 0.3 % of this area

Yorktown Formation: fossiliferous clay with varying amounts of fine-grained sand, bluish gray, shell material commonly concentrated in lenses; mainly in area north of Neuse River. Duplin Formation: shelly, medium- to coarse-grained sand, sandy marl, and limestone, bluish gray; mainly in area south of Neuse River.

Swamp (Quaternary) at surface, covers < 0.1 % 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.