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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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Legend and Rock Ages
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Rio Grande Rift

  map of Rio Grande RiftThe mid-section of the continent is being pulled apart by extensional forces. Volcanism accompanies this activity. The upper Rio Grande River flows southward through New Mexico within a long fault-bounded basin, the Rio Grande Rift, where lava from a source deep in the mantle periodically spreads across the surface. In the near geologic future, several million years or so, a youthful ocean basin may occupy this area.