Geologic units in Logan county, Arkansas

Atoka Formation - Upper part (Middle Pennsylvanian- Atokan) at surface, covers 40 % of this area

Atoka Formation - Upper part

Harthshorne Sandstone (Middle Pennsylvanian- Des Moinesian) at surface, covers 14 % of this area

Harthshorne Sandstone

McAlester Formation (Middle Pennsylvanian- Des Moinesian) at surface, covers 14 % of this area

McAlester Formation

Atoka Formation - Middle part (Middle Pennsylvanian- Atokan) at surface, covers 13 % of this area

Atoka Formation - Middle part

Savanna Formation (Late Pennsylvanian- Des Moinesian) at surface, covers 13 % of this area

Savanna Formation

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

Alluvial deposits of present streams

Atoka Formation - Lower part (Middle Pennsylvanian- Atokan) at surface, covers 2 % of this area

Atoka Formation - Lower part

Terrace deposits (Late Pleistocene) at surface, covers 0.7 % of this area

Alluvial deposits on one or more terrace levels

Boggy Formation (Late Pennsylvanian- Des Moinesian) at surface, covers < 0.1 % of this area

Boggy Formation