Geologic units in Johnson county, Illinois

Upper Pope Group (Tar Springs Sandstone through Kinkaid Limestone) (Mississippian (Serpukhovian)) at surface, covers 35 % of this area

Upper Pope Group (Tar Springs Sandstone through Kinkaid Limestone).

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 30 % of this area

Tradewater Formation

Lower Pope Group (Aux Vases Sandstone through Glen Dean Limestone) (Mississippian (Visean)) at surface, covers 19 % of this area

Lower Pope Group (Aux Vases Sandstone through Glen Dean Limestone).

Caseyville Formation (Pennsylvanian (Bashkirian)) at surface, covers 12 % of this area

Caseyville Formation

Ste. Genevieve Limestone (Mississippian (Visean)) at surface, covers 4 % of this area

Ste. Genevieve Limestone.

St. Louis Limestone (Mississippian (Visean)) at surface, covers 0.4 % of this area

St. Louis Limestone.