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Geologic Map
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Generalized Geologic Map of the Conterminous United States
North America Shaded Relief


  The North American Tapestry of Time and Terrain

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Superior Upland

  Close-up of
 the Superior Upland

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.