Rocky Mountains

Rocky Mountains, principal range of the western region of North America. Extending from north Alaska for more than 3,000 mi (4,800 km) to New Mexico, they form the Continental Divide; rivers rising on the eastern slopes flow to the Arctic or Atlantic Ocean, and those rising on the western slopes flow toward the Pacific. Rivers originating in the Rockies include the Missouri, Rio Grande, Colorado, Columbia, and Arkansas. A relatively new system, the Rockies were formed by massive uplifting forces that began about 70 million years ago.