Geologic units in McDonough county, Illinois

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 41 % of this area

Carbondale Formation.

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 41 % of this area

Tradewater Formation

Warsaw Formation and Salem Limestone (Mississippian (Visean)) at surface, covers 12 % of this area

Warsaw Formation and Salem Limestone in western Illinois.

Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone (Mississippian (Tourniaisian to Visean)) at surface, covers 4 % of this area

Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone.

St. Louis Limestone (Mississippian (Visean)) at surface, covers 3 % of this area

St. Louis Limestone.