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.