<P> The Rocky Mountains took shape during an intense period of plate tectonic activity that resulted in much of the rugged landscape of the western North America . The Laramide orogeny , about 80 -- 55 million years ago , was the last of the three episodes and was responsible for raising the Rocky Mountains . Subsequent erosion by glaciers has created the current form of the mountains . </P>
how did the u.s. rocky mountains come to look the way they do today
erosion by glaciers