Geologic units in Alger county, Michigan

Prairie du Chien Group (Early Ordovician) at surface, covers 29 % of this area

Prairie du Chien Group

Trempealeau Formation (Late Cambrian) at surface, covers 22 % of this area

Trempealeau Formation

Black River Limestone (Late Ordovician) at surface, covers 14 % of this area

Black River Limestone

Munising Formation (Late Cambrian) at surface, covers 13 % of this area

Munising Formation

Trenton Limestone (Late Ordovician) at surface, covers 11 % of this area

Trenton Limestone

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 10 % of this area

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Collingwood Limestone (Late Ordovician) at surface, covers 0.2 % of this area

Collingwood Limestone

Utica Shale (Late Ordovician) at surface, covers < 0.1 % of this area

Utica Shale