The Loess Hills National Scenic Byway meanders 200 miles through western Iowa and (barely) into South Dakota. Loess (pronounced LUSS) is wind blown soil deposits with depths of over 200 feet. The deposits were formed at the end of the last Ice Age--about 18,00 years ago--when retreating glaciers left behind a soil that was ground as fine as flour. The dunes were formed when prevailing winds blew the particles to the eastern bank of the Missouri River. A layer of topsoil has stabilized these dunes, but they are fragile. Loess Hills of this magnitude are found only here and in China.