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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

Introduction
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Legend and Rock Ages
Rock Types
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  Legend and Rock Ages
 

Paleogene Rocks - 66 to 24 million years ago

map of paleogene rocks

  With the dinosaurs extinct, mammals, birds and reptiles flourished on land. Grass also appeared during the Paleogene. An event called the Laramide uplift occurred beneath the western continent, creating the Black Hills and volcanoes in the eastern Rocky Mountains. A hot spot beneath the continental crust caused still more volcanism in the northwestern U.S., forming the Snake River Plain and, currently, the volcanic character of the Yellowstone region.

Other features associated with this time period include the Olympic Peninsula, the Coastal Plain, the Fall Line, and the Rocky Mountains.