During the most recent Ice Age large parts of central and northern Iowa were covered by glaciers. When those masses of ice retreated (or melted) they left their mark across this land.
In north central Iowa, the large expanse of fertile land known as the Des Moines Lobe, was once covered by an extension of the Wisconsin Glacier. It's a very flat area that's punctuated by a scattering of gently rolling hills. This area is famous for being the most productive corn-producing land in the entire United States, and possibly the world. Further to the south the Southern Drift Plains (prairie land west - forest in the east) cover about one third of Iowa.
In the far northeast the elevated deeply-ridged bedrock that fronts the Mississippi River is called the Paleozoic Plateau. In the far west the Loess Hills (or low mountains) stretch along much of the western border with Nebraska, then giving way to the 250-foot-high bluffs that rise above the Missouri River. Further to the north in the rolling hill's landscape of the Northwest Iowa Plains sits the state's highest point.
The Mississippi and Missouri are Iowa's most important rivers. The Mississippi rises in northwestern Minnesota, then flows south to the Gulf of Mexico, just below the city of New Orleans. It is a significant transportation artery and when combined with its major tributaries (the Missouri and Ohio rivers) it becomes the third largest river system in the world at (2,339 miles) (3,765 km) in length.
The Missouri rises in southern Montana in the Rocky Mountains, first flowing north then generally southeast across the heart of the United States, ending at the Mississippi River, just to the north of St. Louis, Missouri.
Many dozens of small lakes are scattered about the state, and additional rivers of note include the Cedar and Des Moines.
For a detailed look at the topography of Iowa, view this map.