Geologic units in Williamson county, Illinois

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 41 % of this area

Shelburn-Patoka Formations undivided.

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 36 % of this area

Tradewater Formation

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 22 % of this area

Carbondale Formation.

Bond Formation (Pennsylvanian (Kasimovian)) at surface, covers 2 % of this area

Bond Formation

Caseyville Formation (Pennsylvanian (Bashkirian)) at surface, covers < 0.1 % of this area

Caseyville Formation