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The Keweenaw Fault is a reverse fault that bisects the Keweenaw Peninsula of the Upper Peninsula of Michigan. The fault is the boundary between the Midcontinent Rift System and adjacent Precambrian terrain. The peninsula, itself, is the southeastern side of a large syncline beneath Lake Superior. The northwestern side forms Isle Royale.
The fault is more than 100 miles (160 kilometers) long and traces a northwesterly path. The fault is most likely younger than the Jacobsville Formation and the Devonian Period.
An seismic event in 1906 claimed to be an earthquake has been attributed to a rock burst, as the area has been significantly mined.
The Natural Wall
One significant feature along the Keweenaw Fault is known as the Natural Wall. The Wall is a near-vertical slope of sandstone at a maximum inclination of 85°.