Geologic units in Yell county, Arkansas

Atoka Formation - Lower part (Middle Pennsylvanian- Atokan) at surface, covers 30 % of this area

Atoka Formation - Lower part

Atoka Formation - Middle part (Middle Pennsylvanian- Atokan) at surface, covers 27 % of this area

Atoka Formation - Middle part

Atoka Formation - Upper part (Middle Pennsylvanian- Atokan) at surface, covers 21 % of this area

Atoka Formation - Upper part

Jackfork Sandstone (Early Pennsylvanian- Morrowan) at surface, covers 7 % of this area

Jackfork Sandstone

Johns Valley Shale (Early Pennsylvanian- Morrowan) at surface, covers 5 % of this area

Johns Valley Shale

Alluvium (Holocene) at surface, covers 5 % of this area

Alluvial deposits of present streams

Harthshorne Sandstone (Middle Pennsylvanian- Des Moinesian) at surface, covers 3 % of this area

Harthshorne Sandstone

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

Alluvial deposits on one or more terrace levels

McAlester Formation (Middle Pennsylvanian- Des Moinesian) at surface, covers 0.8 % of this area

McAlester Formation

Stanley Shale (Early Mississippian) at surface, covers 0.7 % of this area

Stanley Shale - Includes Chickasaw Creek Chert equivalent of Harlton (1938) near top and Hatton Tuff Lentil and Hot Springs Sandstone Member near base