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THE SOILS OF NEBRASKA
are foreign. They came originally from silty sediments of rivers draining
the eastward-facing ranges of the ancestral Rocky Mountains. These
sediments were later extracted from the surface layers of Tertiary
and Pleistocene deposits and wind-carried up to several hundred kilometers,
probably during dry and windy interglacial periods. They drifted mostly
eastward and southward, to be deposited blanketlike over much of
southeastern nebrsaska and parts of northern Kansas and extreme western
Iowa.
They are now mainly to be found between the Sandhills and the lower lands
lying somewhat farther east toward the Missouri Valley, where later glacial
till
subsequently covered or variably replaced them, obscuring their windy
origins.
In some places in eastern Nebraska and in the loess hills of extreme western
Iowa, this silty blanket extends to a depth of as much as 50 meters. Water
is readily able to penetrate such uniformly sized substrate materials, and
the calcium-rich soils that have developed above them are not only very
uniform in texture but also relatively low in organic matter.
Over time, wind and water erosion in the loess hills region have produced
a pattern of gently undulating valleys, hills, and small bluffs. The
steeper slopes of the hills and bluffs often take the form of small
but nearly vertical-walled canyons, with many vertical cleavage
fissures in the soft loess substrate. Along these cleavages the loess tends
to break and slide doward repeatedly, eventually producing a distinctive
"cat-step" erosion pattern that resembles a series of natural, nearly
hoizonatal terraces or steps. Overgrazing by large mammals can easily
aggravate these erosive effects.
This region, traditionally described geographically as the Loess Hills
and Plains (or Rolling Hills and Dissected Plains) of Nebraska, covers
several thousand square kilometers of the state and is roughly bisected
by the Platte River. A general geographic transition area between the
shortgrass plains and sandhills to the west and the Missouri Valley to
the east, it is also a botanical transition area. Although the native
vegetation of the loess hills is largely mixed-grass prairie, some local
areas are dominated by short grasses, and others — usually on
north-facing slopes and on lowlands — approach typical tallgrass
prairie. These more mesic sites, like the tallgrass prairies to the east,
were among the first to be plowed and converted to dry-land farming. Many
of the other areas of the Loess Hills are still only marginal for
nonirrigated crop growing but provide important rangeland resources
for regional farmers and ranchers.
Reprinted with permission
from This Fragile Land
Copyright © 19
by Paul A Johnsgard
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