Geologic units in Columbia county, Arkansas

Claibourne Group (Middle Eocene) at surface, covers 70 % of this area

Claibourne Group

Alluvium (Holocene) at surface, covers 19 % of this area

Alluvial deposits of present streams

Terrace deposits (Late Pleistocene) at surface, covers 10 % of this area

Alluvial deposits on one or more terrace levels

Cockfield Formation (Eocene) at surface, covers < 0.1 % of this area

Brown lignitic clays, silts and sands; some sideritic glauconite may weather to brown ironstone in lower part.

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

Gray to brownish gray clay and silty clay, reddish brown in the Red River Valley, some sand and gravel locally.

Cook Mountain Formation (Eocene) at surface, covers < 0.1 % of this area

Greenish gray sideritic clay in upper part may weather to brown ironstone; yellow to brown clays and fossiliferous marl in lower part may weather to black soil. Ironstone concretions near base.