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Geologic units in Johnson county, Arkansas

Atoka Formation, undivided (Middle Pennsylvanian- Atokan) at surface, covers 66 % of this area

Atoka Formation, undivided

McAlester Formation (Middle Pennsylvanian- Des Moinesian) at surface, covers 9 % of this area

McAlester Formation

Bloyd Shale, and Prairie Grove Member of the Hale Formation (Middle Pennsylvanian- Morrowan) at surface, covers 9 % of this area

Bloyd Shale, and Prairie Grove Member of the Hale Formation

Harthshorne Sandstone (Middle Pennsylvanian- Des Moinesian) at surface, covers 7 % of this area

Harthshorne Sandstone

Savanna Formation (Late Pennsylvanian- Des Moinesian) at surface, covers 4 % of this area

Savanna Formation

Alluvium (Holocene) at surface, covers 3 % of this area

Alluvial deposits of present streams

Terrace deposits (Late Pleistocene) at surface, covers 1 % of this area

Alluvial deposits on one or more terrace levels

Cane Hill Member of Hale Formation (Early Pennsylvanian- Morrowan) at surface, covers 0.5 % of this area

Cane Hill Member of Hale Formation