Geologic units in Calhoun county, Illinois

Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone (Mississippian (Tourniaisian to Visean)) at surface, covers 23 % of this area

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

Glen Park Formation, Hannibal Shale, Chouteau Limestone, McCraney Limestone, Prospect Hill Siltstone, and Starrs Cave Limestone (Mississippian (Tourniaisian)) at surface, covers 17 % of this area

Glen Park Formation, Hannibal Shale, Chouteau Limestone, McCraney Limestone, Prospect Hill Siltstone, and Starrs Cave Limestone.

St. Louis Limestone (Mississippian (Visean)) at surface, covers 11 % of this area

St. Louis Limestone.

Kimmswick (Trenton) Limestone and Decorah Formation (Upper Ordovician (Stage 6)) at surface, covers 8 % of this area

Kimmswick (Trenton) Limestone and Decorah Formation in southern and western Illinois.

Maquoketa Formation or Group (Upper Ordovician (Stage 6 to Hirnatian)) at surface, covers 8 % of this area

Maquoketa Formation or Group, includes Cape Limestone, Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Leemon Formation in southern Illinois; includes Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois; includes Noix Oolite in western Illinois.

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone (Middle Devonian (Givetian) to Upper Devonian (Fammenian)) at surface, covers 7 % of this area

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone.

Silurian System undivided (Silurian (Llandovery to Pridoli)) at surface, covers 6 % of this area

Silurian System undivided, includes Sexton Creek Limestone, St. Clair Limestone, and Moccasin Springs Formation in southern Illinois; includes Wilhelmi Formation, Elwood Dolomite, Kankakee Dolomite, Joliet Dolomite, Sugar Run Dolomite, and Racine Dolomite in northeastern Illinois; includes Mosalem, Tete des Morts, Blanding, Sweeney, Marcus, and Racine Dolomites in northwestern Illinois.

Muscatatuck Group (Middle Devonian (Eifelian to Givetian)) at surface, covers 5 % of this area

Muscatatuck Group, includes Grand Tower Limestone and St. Laurent (Alto and Lingle) Formation in southern Illinois; includes Detroit River Formation, Wapsipinicon Limestone, and Cedar Valley Limestone in northern and western Illinois.

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 4 % of this area

Tradewater Formation

Warsaw Formation and Salem Limestone (Mississippian (Visean)) at surface, covers 3 % of this area

Warsaw Formation and Salem Limestone in western Illinois.

Ancell Group (Middle Ordovician (Darriwillian) to Upper Ordovician (Stage 5)) at surface, covers 3 % of this area

Ancell Group, includes St. Peter Sandstone, Dutchtown Limestone, Joachim Dolomite, and Glenwood Formation; includes Prairie du Chien Group in Jo Daviess County of northwestern Illinois.

Platteville Group (Upper Ordovician (Stage 5)) at surface, covers 3 % of this area

Platteville Group, includes Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill Formations; includes Plattin Limestone in southwestern Illinois.

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 1 % of this area

Carbondale Formation.

Holocene series (Quaternary-Holocene Series) at surface, covers 0.3 % of this area

Alluvium - clay, silt, sand, and gravel.