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 National
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".
The Southern Loess Hills encompass
Mills County and Fremont County
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 paleontological 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.