The highest point in Illinois, Charles Mound, near Apple River, rises only 1,235 feet (376 m) above sea level.
During the last Ice Age, glaciers spread across the region and flattened it.
But those same glaciers left behind materials that became the fertile soils that have made Illinois a leading agricultural state.
The Chicago River, which now flows out of Lake Michigan, used to run in the opposite direction.
In 1900, engineers reversed its flow when they completed the Chicago Sanitary and Ship Canal.
Today people call it “the river that flows backward.”