Geologic units in Allendale county, South Carolina

Duplin Formation (Pliocene) at surface, covers 44 % of this area

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

Huber/Lisbon/Barnwell Formations, undivided (Eocene) at surface, covers 28 % of this area

Poorly to well sorted sand, clay and carbonates deposited in delta-dominated fluvial- and open-marine environments. Unit is characterized by commercial kaolin bodies in older strata from westernmost South Carolina to central Georgia. Younger strata are cyclic marine deposits which deeper water facies exposed in western Georgia. Carbonate facies are locally mined in western Georgia for agricultural lime.

Neogene strata (undifferentiated) (Neogene) at surface, covers 11 % of this area

Poorly sorted clayey sand and gravel deposited in a fluvial environment in South Carolina but becoming more fluvio-marine in Georgia. Unit is characterized by insitu weathered feldspar and an abundance of quartzite gravel and cobbles.

Alluvial Valley Swamp (Quaternary) at surface, covers 10 % 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.

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

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

Penholoway Formation (Pleistocene) at surface, covers 2 % 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 1 % of this area

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

Stream alluvium (Quaternary) at surface, covers < 0.1 % of this area

Stream alluvium and undifferentiated terrace deposits