Which two regions are named because of physical features that common to the group US states?

1) The Great Plains: This region is named for its vast, flat expanses of land. It includes the states of Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming.

2) The Rocky Mountains: This region is named for the towering mountain range that runs through it. It includes the states of Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming.