WSP04621 - Laserfiche WebLink

Home Browse Search

f The Picturesque Ozark Plateaus Areas properly defjned as "mountains" include primarily the Ro~k}' Mountains of CoJofJdo, Wyoming, and Montana in the western part of tile basin, and the Black Hills of western South Dakota. Slopes 3nd stream gradients generally are steep, and natural erosion - while slow in most places with heavy vegetative cover ami boulder-armored channels - is rapid where soft rocks ::Ire exposed. However, the sediment contributed to streams is not excessive. The mountain areas are ust.'d prim~irily for timber, grazing, wildlife habitat. and recreatioll. These areas are especially important as sources of water supply. In the north.central part of the Great Plains in the Dakotas and Montana, and in the large intermountain valleys of Wyoming. are found the basin's "rough lands and {;adlands:' These are vast and rather high areas where the bedrocks consist largely of sIltstone. soft shale, clay, and soft and hard sandstones. Natural vegetation is relatively sparse, offering little protection from erosion which is extremely active. Soils generally are shallow. Grazing is the prll1dpalbnd use, although narrow Jreas of deep alluvial soils Jre suitable for and generally devoted to irrigatiun or dry farming. The "hilly lands" appear intermittently from the bluffs of the Missouri River III western Missouri and Iowa to the foothills of the Rocky Mountains. Here the soils vary from shallow to deep. but Illost uf them are capable of supporting a good natural growth of grasses or trees. Erosion has become very rapid where sllch lands are cultivated without proper conservation management. 10 Much of the hilly land is grazed. but substantial areas in the eastern part are used for c1ean-tiJled crops. In the wooded Ozark Plateaus in Missouri south of the Missouri River, and in the grassy Flint Hills of Kansas, are found the "hilly to mountainous lands." Their parent material is largely hard sedimentary bedrock and the soils vary from very shallow to quite deep. Ordinarily slow. erosion is fairly rapid where the land has been deforested or overgrazed. While general farming and fruit growing occur in more favored locations, the major land areas are used for timber production. grazll1g. and wildlife habita'!. "Moderately sloping lands" are found mostly in areas of soft rocks, glacial till, and loess, interspersed with a few reaches of hard rocks. Soils range from moderately deep to very deep. with some shallow soils and rock outcrops. Most of these areas originally supported tall grasses in the eastern parts and short grasses in the dryer western parts, and natural erosion was moderate. Today a large share of the land IS used for cultivated crops. especially in the central and eastern parts of the basin, and there is some erosion. Farther west in the more arid climate, grazing predominates in the land use pattern. "Intermountain valleys" are areas of more uniform topography within the Rocky Mountains in which signil1cant farming occurs. Silty, clayey. or sandy sediments accumulated more rapidly than the streams were able to remove them, and these sediments have formed moderately deep to deep soils which generally show only moderate erosion. Their most important uses are for irrigation farming, dry farming, and the produc- tion of native hay. The "hullllllocky (dune) lands" indude the 24,OOO-square-miJe Sand Hills area of north-centraJ Nebraska and similar smaller areas in other states. These lands consist of hummocky reaches of loose dune sand currently stabilized by grasses. There 3re thousands of small basins. some of them semi-marshy and others dry. with many slllall lakes representing exposures of the ground-water table. Soils generally are thin, though the loose sand deposits are rather thick. An aeolian topography together with the sandy soils produce very little direct runoff to streamnow, but streams in the area accumulate unusually steady flows. mostly from ground-water accretions. The streams transport a great deal of sand derived from their channels and limited tributary drainage areas. Land erosion is almost entirely by wind and varies with the condition of the grass cover. Such areas are devoted mostly to grazmg. "Level lands and undulating glacial drifl" are underlain by alluvium, loess. and glacial drift of gre3tly varying character. Their soils are generally deep to very deep, and natural erosion is quite slow. Water erosion IS active at higher levels. with the soils washed frolll the knolls usually collecting in intervening low areas. Most