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


  The North American Tapestry of Time and Terrain

The Two Maps
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Legend and Rock Ages
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Great Plains

  Close-up of
 great plainsThe Great Plains, a broad, flat, mostly green band down the center of the map, is a vast east-tilted surface formed by deposition of sediment eroded from the uplifting Rocky Mountains in the Neogene and Paleogene, beginning about 65 million years ago. This region is now being eroded, especially on its eastern margin, by numerous east-flowing rivers that are exposing the older rocks beneath. To the west, these older, largely Cretaceous, sedimentary rocks contain some of the continent's most spectacular dinosaur fossils.