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

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  Legend and Rock Ages
 

Cretaceous Rocks - 146 to 66 million years ago

map of cretaceous rocks

 

Throughout the Cretaceous the Rockies continued to grow taller while the shallow Mowry Sea covered the length of the central continent. Over time this sea retreated to the south into the area now called the Gulf of Mexico.

Although dinosaurs continued to flourish through the Cretaceous, with species like the tyrannosaurus and triceratops proliferating, the most famous Cretaceous event was the mass extinction that marks its end. All large land animals were killed, and up to 70% of marine life was also destroyed. The ammonites, shelled marine predators, were driven to extinction along with the dinosaurs. The extinction is believed to have resulted from a huge asteroid that hit the earth in the vicinity of the Yucutan Peninsula. This crater, the Chixulub crater has since been filled in with sediments.

Other major features that are linked to the Cretaceous due to the timing of their formation or the age of their rocks include the Coteau des Praires, the "strange grain", the Sierra Nevada, the Rocky Mountains, the Great Plains, and Walker Lane.