Geologic units in Washington county, Illinois

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 61 % of this area

Shelburn-Patoka Formations undivided.

Bond Formation (Pennsylvanian (Kasimovian)) at surface, covers 38 % of this area

Bond Formation

Mattoon Formation (Pennsylvanian (Kasimovian)) at surface, covers 0.4 % of this area

Mattoon Formation.