Geologic units in Ionia county, Michigan

Saginaw Formation (Pennsylvanian) at surface, covers 71 % of this area

Saginaw Formation

Michigan Formation (Mississippian) at surface, covers 9 % of this area

Michigan Formation

Red beds (Jurassic) at surface, covers 8 % of this area

Red beds

Grand River Formation (Pennsylvanian) at surface, covers 8 % of this area

Grand River Formation

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

Bayport Limestone