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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.
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