Geologic units in Stark county, Illinois

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 52 % of this area

Carbondale Formation.

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 48 % of this area

Shelburn-Patoka Formations undivided.