Illinois harnesses wind energy through turbines and is located near large bodies of water that produce wind. Corn is Illinois's primary crop and provides 40% of the US's ethanol, while farmers work to improve production. Charles Mound is Illinois's highest point at 1,235 feet, and the Mississippi River, which flows through the state, is the lowest at 279 feet above sea level. Tourists can retrace colonists' journeys by taking barge tours down the Mississippi River.