Flanking the state's western border, the Loess Hills National Scenic Byway passes through a unique land formation that's up to fifteen miles wide and about 200 miles long, stretching from near Sioux City, Iowa in the north to St. Joseph, Missouri in the south. The definition of where are the Loess Hills is fairly readily apparent to the naked eye on the western most boundaries of the landform area where steep hills rise above the Missouri River floodplain. The easternmost boundary of the area is derived from looking at several criteria including: slope steepness, depth of loess, summit heights, and local relief to name a few of the factors.
This area encompasses approximately 650,000 acres and extends in largely a narrow band paralleling the Missouri River. The area has exceptionally thick deposits of wind blown silt called loess (pronounced "luss" ) covering steep bluffs, with narrow corrugated ridges and alternating peaks and saddles. In 1985, The National Park Service cited the area as "the best example of loess topography not only in the central lowlands, but in the United States." In 2001, The National Park Service conducted a study to examine the possibility of this region becoming a unit of the NPS. While not feasible, the area was deemed a nationally significant natural and cultural resource.
Geologists like the area because of the unique topography. There are between 200-300 feet of loess soil deposited 15,000-18,000 years ago when the glaciers receded. Over 10,000 acres of the Loess Hills have been classified as a Natioanl Natural Landmark. Loess soil has many unique characteristics that make it a unique resource. Loess will remain remarkably firm and stable when dry and undisturbed enabling the dramatic bluffs to stand erect and intact. Loess soils are also well drained and dry rapidly after a rain. However, if the soil becomes saturated, the loess particles slump or collapse downward as a unit, created formations called "cat steps".
Biologists delight in the Loess Hills for two primary reasons: (1) because it is the western most range of the eastern deciduous species, and the eastern most range of the western plains species, making this an area of significant biological crossroads and (2) this area harbors over 20,000 acres of remnant prairie representing about 75% of Iowa's remaining prairie heritage, of which 99.9% is already lost.
From a paleoontological standpoint, the Loess Hills hold significant fossil assemblages, making it one of the richest areas for such research in the state of Iowa. Fossils found in the area include mammoths, mastodons, giant sloths, caribou, and giant beaver.
And archaeologically this area has had a rich history of human inhabitation. River trade inhabitants and earth lodges are but a few of the significant areas of focus for archaeological research.