Geologic units in Howard county, Arkansas

Stanley Shale (Early Mississippian) at surface, covers 38 % 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

Tokio Formation (Late Cretaceous) at surface, covers 14 % of this area

Tokio Formation

Trinity Group (Early Cretaceous) at surface, covers 11 % of this area

Trinity Group

Alluvium (Holocene) at surface, covers 11 % of this area

Alluvial deposits of present streams

Woodbine Formation (Late Cretaceous) at surface, covers 5 % of this area

Woodbine Formation

Jackfork Sandstone (Early Pennsylvanian- Morrowan) at surface, covers 5 % of this area

Jackfork Sandstone

Terrace deposits (Late Pleistocene) at surface, covers 4 % of this area

Alluvial deposits on one or more terrace levels

Brownstown Marl (Late Cretaceous) at surface, covers 2 % of this area

Brownstown Marl

Ozan Formation (Late Cretaceous) at surface, covers 2 % of this area

Ozan Formation

De Queen Limestone (Early Cretaceous) at surface, covers 2 % of this area

De Queen Limestone

Marlbrook Marl (Late Cretaceous) at surface, covers 2 % of this area

Marlbrook Marl

Dierks Limestone (Early Cretaceous) at surface, covers 1 % of this area

Dierks Limestone

Johns Valley Shale (Early Pennsylvanian- Morrowan) at surface, covers 0.6 % of this area

Johns Valley Shale

Annona Chalk (Late Cretaceous) at surface, covers 0.4 % of this area

Annona Chalk

Sartoga Chalk (Late Cretaceous) at surface, covers 0.3 % of this area

Sartoga Chalk

Nacatoch Sand (Late Cretaceous) at surface, covers 0.2 % of this area

Nacatoch Sand

Arkansas Novaculite (Early Mississippian to Late Devonian) at surface, covers 0.1 % of this area

Includes upper division (Mississippian), middle division (Mississippian and Devonian), and lower division (Devonian)