Geologic units in Union county, Arkansas

Claibourne Group (Middle Eocene) at surface, covers 74 % of this area

Claibourne Group

Alluvium (Holocene) at surface, covers 26 % of this area

Alluvial deposits of present streams

Terrace deposits (Late Pleistocene) at surface, covers 0.4 % 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.