In the past, people thought of the land between the Appalachian and Rocky Mountains as the "middle" of the West. That is why this region is called the Middle West. The major landform is the Interior Plains which are made up of two parts. To the east are the Central Plains. To the west are the Great Plains. The Central Plains are not much higher than sea level in some places. On the western edge of the Great Plains the land is higher than 3,000 feet above sea level. Four of the Great Lakes are in the Middle West. They are Lakes Superior, Michigan, Huron, and Erie. Together with Lake Ontario, all five form the largest body of fresh water in the world.