Comprising the western third of the state of Kansas is the physiographic region known as the High Plains. Ranging in elevation from approximately 800m to 1,200m above sea level, the High Plains region is characterized primarily by high tableland with a few gently rolling hills and valleys. During the Pleistocene, glaciation occurred to the north in the Missouri Plateau and to the west in the Rocky Mountains U.S. Geological Survey, 2006). As glaciers retreated at the end of the last ice age, sand and finely ground silt from underlying rock and sediment were deposited and have been transported by outwash from the melting glaciers and by wind. Known as loess, this wind-driven silt now covers the High Plains of Kansas (Kansas Geological Survey, 1999). Another feature of the region is the occurrence of depressions with depths as much as thirty meters. Some are characterized by very gentle sloping sides while others are steep. The depressions' shapes range from circular to irregular. They are the result of subsidence as underlying salt, gypsum, limestone, and chalk have dissolved in Permian, Cretaceous, Pliocene, and Pleistocene rocks. A few contain permanent lakes while others hold water only for a short time after rainfall (Frye, 1950).
Image from U.S. Geological Survey's Ground Water Resources Program photo gallery.
A giant alluvial fan resulted from the merging of smaller alluvial fans created by an array of braided streams flowing easterly and transporting Tertiary and Quaternary sediments from the Rocky Mountains (Kansas Geological Survey, 2004). Surface water of the region flows intermittently across broad, gentle terrain creating drainage patterns that fan out from the western part of the state in an easterly trend as the elevation decreases from west to east (Kansas Geological Survey, 2005). Underlying the Kansas High Plains is the Ogallala-High Plains Aquifer, the primary source of high quality groundwater for the region. This aquifer system has decreased in capacity over the past decades due to heavy demands for irrigation. In this semi-arid climate, recharge by streams and precipitation has not kept up with demand. In the 1800s, settlers in the area described an "unending supply of water," a description which is no longer true. Because of an increasingly warmer and drier climate and overuse by agriculture, the aquifer's ability to continue supplying Kansas' commercial and residential dependents with the quantity and quality of water to which they are accustomed is questionable (Bruce, 2000).
Map from Kansas Geological Survey.
During the Cretaceous Period, from 144 million years ago to 65 million years ago, approximately one-half of Kansas, from northeast to southwest, was covered by a shallow interior sea, which stretched from the Arctic Circle southward to the Gulf of Mexico. Known as the Western Interior Sea or Inland Sea, this huge body of water covered most of the modern Midwest and Canada, and was inhabited by such marine life as giant clams, sharks, mosasaurs, ammonites, and plesiosaurs. As the Cretaceous came to an end, the Interior Sea became shallower as uplift formed the Rocky Mountains during the Tertiary Period, and western Kansas was raised above sea level. During the Pleistocene, glaciers to the north and west pulverized rocks and sediments, retreated, and dropped the sand and loess which covers today's High Plains (Trimble, 1980).Map from Mike Everhart, Oceans of Kansas Paleontology
Underlying the High Plains are late Tertiary conglomerates and sandstones, Tertiary and Cretaceous shales, and Cretaceous limestones, covered by Quaternary sands and loess, and in stream valleys, Quaternary alluvial deposits. Unconsolidated subsurface sands, gravels, and clays make up the Ogallala Formation, from which the water of the Ogallala-High Plains Aquifer is depended upon by the region. Mortar beds, porous materials cemented by calcium carbonate, define the eastern edge of the High Plains. These mortar beds are exposed where shallower sand and loess deposits have eroded (Kansas Geological Survey, 1999).
Images of mortar beds from University of Michigan.
Geological evidence indicates that, until the end of the Cretaceous Period, the High Plains region was a shallow marine environment. During the Tertiary Period as uplift formed the Rocky Mountains, the sea floor was raised. Flooding streams, loaded with gravel, pebbles, sand, and silt, flowed eastward out of the mountains forming alluvial fans which coalesced into the Ogallala formation (Kansas Geological Survey, 2003). The Pleistocene epoch began approximately 2.5 million years ago, giving rise to the ice age responsible for much of the geomorphology of the region. Ice sheets to the north and west advanced and receded about every 41,000 years until the last 700,000 years, which has seen this cycle repeated at approximately 100,000-year intervals. During the 100,000-year climate variations, each cycle has consisted of an 85,000-year glacial period characterized by an unstable, colder climate, followed by an interglacial period of 10,000-15,000 years when more stablility and warmer climate is the rule. The Last Glacial Maximum (LGM) occurred some 17,000 to 21,000 years ago. During this time, the ice sheet of the northern United States and Canada influenced the track of westerly storms, causing an increase in rainfall and lake levels in the region as evidenced by erosion of ancient drainage systems (Thurmond, 1999).
According to the United States Department of Agriculture's Forest Service, the High Plains region has a climate classified as "Great Plains-Palouse Dry Steppe." Today's climate is actually the latter part of an interglacial period and began around 10,000 years ago. The average precipitation for the High Plains of Kansas ranges from 400 to 530 mm per year. Combined with an annual average temperature of 10-14 degrees Celsius, the region's growing season lasts from 140-185 days (U.S. Department of Agriculture, 1994). This semiarid climate is quite variable and both very wet and very dry periods are not uncommon. Several severe droughts occurred during the twentieth century. Perhaps the most famous is the Dust Bowl drought, which lasted some seven years and was responsible for the agricultural and economic calamity which sent millions of people migrating from the Great Plains to the western United States just to survive (Young, 2002).
Photo of 1937 dust storm from Library of Congress.
The Kansas Native Plant Society divides the High Plains Region into four ecoregions. The Rolling Sand Plains subregion (25b) consists of 2,661 square miles of rolling plains with active dunes and a few perennial streams. Natural vegetation found in the Rolling Sand Plains is a mixture of sand sagebrush, sand bluestem, prairie sandreed, and little bluestem. The second ecoregion is termed Moderate Relief Rangeland (25c). Encompassing 3,084 square miles of the High Plains, this ecoregion is made up of irregular moderately sloped plains, a few large streams, and intermittent streams. Blue grama and buffalograss make up the area's upland natural ground cover while slopes, soils ajoining rivers and streams, areas with thick loess deposits, and the south's chalk flat prairie have more cover of little bluestem and side oats grama. The third ecoregion is called Flat to Rolling Cropland (25d) and is 17,882 square miles of flat to rolling plains with a few intermittent streams. The northern portion of this ecoregion is a mixedgrass prairie with blue grama, needle and thread, prairie sandreed, threadleaf sedge, and western wheatgrass. Inland saltgrass, blue grama, buffalograss, alkali sacaton, and western wheatgrass make up the shortgrass prairie of the southern Flat to Rolling Cropland ecoregion. The final ecoregion of the High Plains is called Rolling Cropland and Range (25e). This 765-square-mile level-to-rolling plains area also is characterized by a few intermittent streams, loess-mantled areas, and areas with course-textured soils. Natural ground cover for the loess-mantled areas is the shortgrass prairie variety of buffalograss, blue grama, alkali sacaton, western wheatgrass, and inland saltgrass. Soils of a coarse texture in this ecoregion grow sand sagebrush, little bluestem, sand bluestem, and prairie sandreed. Areas with this particular mixture of vegetation are referred to as sandsage prairie, or sandsage steppe (Kansas Native Plant Society, 2007).
Map by U.S. Geological Survey
As delineated by the U.S. Department of Agriculture, Kansas' High Plains region is in an ecological subregion termed the Central High Tablelands. This section is almost exclusively utilized by farmers and ranchers. Approximately sixty percent of the area is in cropland, most of it in dryland farming (U.S. Department of Agriculture, 1994). As with natural vegetation, the Kansas Native Plant Society's four ecoregions each have characteristic land uses. The Rolling Sand Plains is mostly rangeland for livestock, but does include some irrigated cropland. The Moderate Relief Rangeland ecoregion is also rangeland for livestock, has some minor dryland farming, and substantal winter wheat and grain sorghum cropping operations. In the Flat to Rolling Cropland ecoregion, winter wheat, corn, grain sorghum, and sugar beets are grown on large areas of irrigated farmland. Some dryland crops are also grown in this subregion. On the Rolling Cropland and Range ecoregion, corn, grain sorghum, alfalfa, and winter wheat are the dominant crops. Some of the area is rangeland, and a substantial amount of the land is bare ground (U.S. Department of Agriculture, 1994).
Photo from Kansas Geological Survey
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