The Mississippi River, which flows through the Mississippi valley, has created a large floodplain over time. This floodplain is made up of alluvial soils, which are soils that have been deposited by rivers. Alluvial soils are typically fertile and well-drained, making them ideal for agriculture.

The Mississippi valley is home to some of the most productive farmland in the United States. This is due in part to the alluvial soils that are found in the valley.