The Black River Escarpment is a geological feature in Eastern Wisconsin

Wisconsin

Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...

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The escarpment runs parallel to and between the Niagara Escarpment

Niagara Escarpment

The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs westward from New York State, through Ontario, Michigan, Wisconsin and Illinois...

 and the Magnesian Escarpment.
The escarpment marks the boundary between bedrock from Lower Magnesian limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 bedrock

Bedrock

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...

 and earlier Black River limestone.
The escarpment emerges from Green Bay

Green Bay

- Geography :Bodies of water* Green Bay , a bay of Wisconsin known to locals as the Bay of Green Bay* Green Bay, Newfoundland and Labrador, a bay located on the island of NewfoundlandMunicipalities* Green Bay, Wisconsin, United States...

, on Lake Michigan

Lake Michigan

Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron...

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The escarpment's boundaries are not always visible to the untrained eye, but are marked by cliffs in some regions.