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

Article

  The North American Tapestry of Time and Terrain

Introduction
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Legend and Rock Ages
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  Features
 

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.