Geological wonder awaits visitors to Iowa's Loess Hills region Silt from melting glaciers was lifted by winds to form the Loess Hills of western Iowa, located along the Missouri River Valley. Located along the Missouri River Valley, the hills were formed thousands of years ago when silt from melting glaciers was lifted by winds to form the hills. Some of the deposits in western Iowa are more than 100 feet thick.
China is the only other place in the world that can boast such thick deposits.
Travelers on Interstate 29 can see the hills, but, for a closer look, there are several spots to consider. The U.S. Department of Interior declared two areas totaling 10,000 acres as National Natural Landmarks. The Turin site is in Monona County, and the Little Sioux-Smith Lake area is in the northern part of Harrison County. Loess Hills Pioneer Forest in southern Monona County preserves some of the geological history of the area. Iowa all preserve parts of the Loess Hills.