Geologic units in Hot Spring county, Arkansas

Stanley Shale (Early Mississippian) at surface, covers 34 % 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

Wilcox Group (Early Eocene) at surface, covers 24 % of this area

Wilcox Group

Alluvium (Holocene) at surface, covers 16 % of this area

Alluvial deposits of present streams

Arkansas Novaculite (Early Mississippian to Late Devonian) at surface, covers 9 % of this area

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

Terrace deposits (Late Pleistocene) at surface, covers 9 % of this area

Alluvial deposits on one or more terrace levels

Missouri Mountain Shale and Baylock Sandstone (Late Silurian) at surface, covers 3 % of this area

The Baylock Sandstone is present only in the Cross, Cossatot, and Trap Mountains. Missouri Mountain Shale is mapped with Polk Creek Shale and Bigfork Chert in the area between Paron, Saline County, and Little Rock.

Jackfork Sandstone (Early Pennsylvanian- Morrowan) at surface, covers 2 % of this area

Jackfork Sandstone

Pole Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician) (Late Ordovician to Middle Ordovician) at surface, covers 1 % of this area

Polk Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician)

Midway Group (Paleocene) at surface, covers 1.0 % of this area

Midway Group

Igneous rocks (Cretaceous) at surface, covers 0.7 % of this area

Includes undifferentiated altered sedimentary rocks of Paleozoic age at Granite Mountain, Pulaski County, and Mufreesboro, Pike County. Acid to intermediate - Nepheline syenite complexes at Magnet Cove and Potash Sulfur Springs, stocks at Granite Mtn., explosion breccias, and dikes and sills (principally trachyte,tinguaite, phonolite, some ranging from syenite to diabase). Basic to ultrabasic - Lamproite pipes (Murfreesboro, Pike County) and dikes and sills (principally lamprophyres of fourchite, ouachitite, and monchiquite).

Johns Valley Shale (Early Pennsylvanian- Morrowan) at surface, covers 0.3 % of this area

Johns Valley Shale

Brownstown Marl (Late Cretaceous) at surface, covers 0.2 % of this area

Brownstown Marl

Womble Shale (Middle Ordovician) (Middle Ordovician) at surface, covers < 0.1 % of this area

Womble Shale (Middle Ordovician)