Geologic units in Kalkaska county, Michigan

Coldwater Shale (Mississippian) at surface, covers 54 % of this area

Coldwater Shale

Michigan Formation (Mississippian) at surface, covers 21 % of this area

Michigan Formation

Marshall Sandstone (Mississippian) at surface, covers 19 % of this area

Marshall Sandstone

Ellsworth Shale (Late Devonian) at surface, covers 3 % of this area

Ellsworth Shale

Antrim Shale (Late Devonian) at surface, covers 2 % of this area

Antrim Shale