The Rocky Mountains are relatively new, formed from 55 million to 80 million years ago (mya) during the Laramide orogeny. North America began to move westwards as Pangaea broke up. A number of tectonic plates began to slide under the North American plate. The angle of subduction was shallow, resulting in a broad belt of mountains running down western North America. Since then, further tectonic activity and erosion by glaciers has sculpted the Rockies into dramatic peaks and valleys. 