Carbondale Formation
(Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 31 % of this area Carbondale Formation.
St. Louis Limestone
(Mississippian (Visean)) at surface, covers 10 % of this area St. Louis Limestone.
Glen Park Formation, Hannibal Shale, Chouteau Limestone, McCraney Limestone, Prospect Hill Siltstone, and Starrs Cave Limestone
(Mississippian (Tourniaisian)) at surface, covers 9 % of this area Glen Park Formation, Hannibal Shale, Chouteau Limestone, McCraney Limestone, Prospect Hill Siltstone, and Starrs Cave Limestone.
Baylis Formation
(Upper Cretaceous (Campanian)) at surface, covers 7 % of this area Baylis Formation (western Illinois).
Tradewater Formation
(Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 6 % of this area Tradewater Formation
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 2 % of this area New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone.
Muscatatuck Group
(Middle Devonian (Eifelian to Givetian)) at surface, covers 0.1 % 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.
Holocene series
(Quaternary-Holocene Series) at surface, covers < 0.1 % of this area Alluvium - clay, silt, sand, and gravel.
