Geologic units in Arenac county, Michigan

Michigan Formation (Mississippian) at surface, covers 68 % of this area

Michigan Formation

Saginaw Formation (Pennsylvanian) at surface, covers 28 % of this area

Saginaw Formation

Marshall Sandstone (Mississippian) at surface, covers 3 % of this area

Marshall Sandstone

Coldwater Shale (Mississippian) at surface, covers 2 % of this area

Coldwater Shale