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The Superior Upland of Wisconsin and Minnesota is the largest U.S.
surface exposure of the ancient (2.6 to 1.6 billion years old) core
of the North American continent, known geologically as the Canadian
Shield. These rocks are from the Precambrian.
Rocks of similar ages have been found in the Beartooth Mountains
of Wyoming, and rocks even older than these have been recognized
in northern Canada. Though the area is of low topographic relief
today, the igneous and metamorphic rocks of the Superior Upland
were part of a mountain rage located at a continental margin. Some
of these rocks have been important sources of iron, copper, and
other industrial minerals.
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