The Loess Hills of western Iowa were formed when glaciers crushed bedrock into floury silt, deposited it on the Missouri River floodplain, and westerly winds carried the fine soil into steep loess dunes more than 200 feet deep, a landform otherwise matched only in western Iowa and the Yellow River valley in China. Extending in a narrow band two to ten miles wide along Iowa's western border, the hills' rugged landscape and distinctive climate and soil support rare native plant and animal communities, from early pasque flowers protected from frost by hairy stems and leaves to taller midsummer flowers that rise above grasses for pollinating insects. Loess, from a German word meaning loose, is composed mainly of quartz silt and is highly erosive, yet its angular grains can stand in steep or vertical faces for years; it also sloughs on steep slopes to form step-like terraces called cat-steps and dissolves readily in water, earning the local nickname sugar clay. The region also holds a nationally significant archaeological record, including more than 1,000 Late Prehistoric Glenwood earthlodges in the south and paired palisaded Mill Creek villages and ancient cornfields in the north, preserving 300 years of cultural diversity from ancestral Plains Indian cultures that lived there at the same time before horses and before metal was introduced to North America. Mill Creek people made tools from stone, pottery, wood, plants, and bone, raised dogs, traded across the Midwest, and created distinctive arrowheads, large pots, and artwork in stone and clay. In local history, Akron's first flour mill and dam were built in 1862 about one-quarter mile from this site, and the first bridge across the Big Sioux connecting Iowa with Dakota Territory was built there in 1880. More recently, the Loess Hills National Scenic Byway began in 1989 as a grassroots effort, became an Iowa Scenic Byway in 1998, and received National Scenic Byway designation in 2000.