Geologic units in Calhoun county, Michigan

Marshall Sandstone (Mississippian) at surface, covers 56 % of this area

Marshall Sandstone

Coldwater Shale (Mississippian) at surface, covers 28 % of this area

Coldwater Shale

Saginaw Formation (Pennsylvanian) at surface, covers 7 % of this area

Saginaw Formation

Bayport Limestone (Mississippian) at surface, covers 5 % of this area

Bayport Limestone

Michigan Formation (Mississippian) at surface, covers 4 % of this area

Michigan Formation