The historian Walter Prescott Webb, in his book "The Great Plains," suggested that the northwest Europeans who settled much of the United States faced three great "environmental encounters" - areas where climatic conditions were so unlike those of their home region that the agricultural crops and settlement patterns developed in Europe were inappropriate. The first of these encounters was with the high summer temperatures and humidity levels of the Southeast. The second was the arid Southwest and interior West. The third was the great continuous grasslands located astride the center of the country (Map 10).
Among the problems on the grasslands, average annual precipitation was much less than in the East, although violent storms accompanied by high winds, hail, and tornadoes were common. Blizzards with wintry blasts intensifying the cold drove the snow into immense drifts. The hot, dry winds of summer parched the soil and sometimes carried it away in great billowing clouds of dust.
The region's sparse natural water supply would not support tree vegetation except along the stream courses. Many of these streams were small and flowed only intermittently. Eastern farmers, accustomed to a plentiful supply of water for crops and animals, as well as ample wood for building, fencing, and heating, had to adapt to quite different conditions in their attempts to settle the Great Plains.
The topography and vegetation of the grasslands is among the least varied to be found anywhere in the United States. Early settlers following the Oregon Trail could reach the Pacific coast in one season of travel, in part because the grasslands were so easy to cross. The region lies entirely within the interior lowlands physiographic province. The underlying sedimentary beds dip gently. Elevation increases gradually, almost imperceptibly, from east to west. Along the eastern margin, the elevation is only 500 meters, whereas in the west, Denver, Colorado, claims an altitude of more than 1,500 meters.
Physiographically, the largest portion of the Great Plains is the High Plains stretching along the western margin of the region from south Texas northward to southern Nebraska. Covered by a thick mantle of sediments that are often quite sandy and extremely porous, this section is generally flat. Only along streams such as at Scottsbluff on the Platte River in western Nebraska or at Palo Duro canyon on the Red River in northwest Texas has erosion resulted in substantial local relief. The Lake Agassiz Basin, formerly occupied by the largest of the Pleistocene lakes, is another exceptionally flat area and includes the valley of the Red River of the North in North Dakota and Minnesota.
Not all portions of the region are so unvarying topographically. The most obvious exception are the Black Hills of South Dakota and Wyoming. A large, dome-shaped area of eroded igneous rock, the Black Hills are associated both geologically and topographically with the Rocky Mountains to the west. In southern Texas, the Edwards Plateau is heavily eroded into a canyonlands landscape along its southeastern margin where it is adjacent to the coastal plain. In central and northwestern Nebraska, the Sand Hills offer a dense, intricate pattern of grass-covered sand dunes, many of which are well over 30 meters high. The dunes were created by sand blowing along the southern margins of continental glaciers during the Pleistocene. Badlands topography - extremely irregular features resulting from wind and water erosion of sedimentary rock - is widespread on the unglaciated Missouri Plateau from northern Nebraska northward to the Missouri River. North of the Missouri River and west of the Lake Agassiz Basin, the glaciated Missouri Plateau, although sometimes flat, is covered with ponds, moraines, and other glacial features.
Although agriculture has destroyed much of the original grasslands vegetation, the moister eastern portions (areas with more than 60 centimeters of annual precipitation in the north or more than 90 centimeters in the south) were originally a continuous tall-grass prairie, where grasses grew between 30 centimeters and 1 meter in height. Along the western margins of the Plains, prairie grasses gave way to bunch grasses - shorter, more separated grasses could succeed in the semiarid conditions of the western Plains.
The prairie grasses have developed deep, intricate root systems that commonly extend much deeper into the soil than the grass blades reach above, allowing them to utilize available water. The tangled root system made the prairies exceptionally difficult to plow. The first settlers often had to employ heavy plows pulled by as many as 20 animals to break the sod. The prairie sod could also be "cut" into large bricks used in the construction of sod houses during the early period of Plains' settlement by Europeans.
The warm, moist tropical maritime air flowing in from the Gulf of Mexico, the prime contributor of moisture to the Plains, commonly curves up the Mississippi Valley and then moves northeast, missing much of the western Great Plains entirely. One result of this pattern is the marked westward decline in average precipitation amounts. In Kansas, for example, average annual precipitation varies from a moist 105 centimeters in the southeast to a semiarid 40 centimeters in the southwest.
Periods of higher than normal precipitation on the Great Plains result when tropical air masses move northwestward from the Gulf of Mexico, which brings these air masses over portions of the Plains. This provident current is far from dependable, however. Fortunately for the Plains farmer, about three-quarters of the precipitation falls during the period of more rapid crop growth, from April to August.
Some of the region's spring and summer precipitation comes in the form of violent thunderstorms. Hail is occasionally a product of these storms. These frozen pellets, sometimes measuring more than 5 centimeters in diameter, have the power to devastate a crop of mature, top-heavy wheat. Much of the southern and west-central Plains experiences frequent hail storms, with parts of western Nebraska and southeastern Wyoming leading the continent in average annual hail frequency.
Tornadoes, which can have funnel wind speeds in excess of 350 kilometers per hour, are another violent result of these storm systems of the Great Plains. Although the area affected by any one funnel is small, the frequent occurrence on the central Plains makes tornadoes a significant regional hazard.
Wind has been a mixed blessing on the Great Plains. Late spring and summer wind velocities on the central and southern Plains are among the highest in interior America. In the past, this served to maximize the efficiency of windmills in the region. However, the persistent winds also mean that the amount of moisture evaporated and transpired by plants is high across much of the region.
The chinook, a winter wind, occurs when dry, relatively warm air from the Pacific Coast pushes over the Rocky Mountains. As it descends onto the Great Plains, it warms still further and is much warmer than the cold, continental air mass commonly found over the region in winter. The Pacific air temporarily pushes the cold air from the western Plains, and a rapid, dramatic temperature rise results. Partly because of this interesting phenomenon, winter temperatures along the higher western area are slightly warmer than along the eastern edge of the Plains.
In addition, the length of the frost-free season varies widely around the average from year to year. As with annual temperature range, the variation increases as one moves northward.
Snow, wind, and cold are all part of one of the most devastating weather elements on the Plains: the blizzard. A blizzard occurs in winter when a very cold polar air mass pushes southward along the Rocky Mountains and onto the Plains, breaking the usual west to east storm pattern. High winds, intense cold, and considerable amounts of snow are associated with these storms. A blizzard can last for several days and bring half of the average winter snowfall. Because Plains ranchers usually leave their livestock outdoors during the winter, a severe blizzard may block an animal's access to food and result in high animal mortality.
The pre-European occupation of the Plains by American Indians was limited. Hunting, particularly for buffalo, was the primary economic activity. Most tribes lived along streams in semipermanent settlements. With no means of rapid long-distance overland movement (the dog was the only domesticated animal in pre-European North America), the Indians could not leave the dependable water supplies of the streams for any long period. This was a substantial problem, for the migration of the great buffalo herds often took this food source far away from the settlements for many weeks.
When the Spanish departed from the southern Plains following their initial explorations, they left some of their horses behind, a "gift" that dramatically altered the lifestyle of the Plains Indians. By the time Americans reached the Plains in the early 19th century, they found what many have called the finest light cavalry in world history. The horse had diffused throughout the grasslands, and the Plains Indians, no longer restricted to the waterways, freely followed the buffalo migration.
The early American perception of the region as an unpromising and difficult place to settle was not totally wrong. The lack of trees meant that farmers had none of the traditional material used for the construction of houses and barns, for fencing, or for fuel. Water sources were scarce; often rivers and streams had only a seasonal flow. Those who arrived early settled along these waterways. The crops that settlers brought with them to the Plains often failed, and crop success varied greatly from year to year as precipitation amounts fluctuated widely. Agricultural production rates were also generally lower, and the 65-hectare farm size that seemed so adequate farther east proved to be too small on the Great Plains.
The settlement frontier hesitated along the eastern boundary of the Plains partly as a result of these problems. Settlers tended to bypass the Plains for the Pacific Coast until technological and land ownership changes made Plains settlement more inviting.
During this hesitation, an alternative economic system swept across the region. An extensive ranching economy had been introduced into south Texas by Spaniards and into east Texas by American settlers from the South. This economy spread from Texas northward during the period from 1867 to 1885.
Great herds of cattle were driven northward from south Texas to railheads in Kansas both for shipment east and to stock the huge, relatively unsettled Plains region. By 1880, perhaps 5 million head of cattle had been moved.
The open-ranching economy collapsed rapidly in the late 1880s. Widespread overgrazing, competition from the superior beef of expanding cattle-raising operations in the Midwest, a slipping national economy, a disastrous winter in 1887-1888, and a rapid influx of farmers onto the Plains combined to end this short period of American history. The open-range, unimproved ranches were pushed to the drier western side of the Plains or were forced into a more restrained fenced operation.
On the agricultural frontier, barbed wire, developed commercially in the 1870s, provided an effective alternative fencing material to take the place of the missing wood supply. For a time, dwellings constructed of sod provided adequate housing. Nevertheless, most settlers replaced them as soon as possible with frame homes. Lumber was brought in by the railroads, which were under construction all across the Plains by the 1870s. The development of a simple windmill and mechanical well-drilling devices meant that sufficient water could be obtained locally for humans and animals, as well as for irrigation. It was the widespread adoption of windmill technology on the grasslands that led to its subsequent acceptance across most of rural America. Grain farming also became increasingly mechanized, enabling farmers to operate larger farms and thus compensate for lower yields.
Finally, crops that were better adapted to the growing conditions of the region were introduced into the agricultural system, and farmers began to improve their understanding of how to use the Plains environment. Hard winter wheat is perhaps the best example. First brought to the United States by Mennonite immigrants from Russia, it was far better adapted to the dry growing conditions of the Great Plains than the wheat strains grown there earlier.
Today, the Great Plains is America's premier wheat-producing region, and it is largely on the abundance of Plains agriculture that the United States is the world's top wheat exporter.
The agriculture of the Great Plains is large scale and machine intensive, dominated by a few crops, the most important of which is wheat. Winter wheat is planted in the fall. Before the winter dormant season sets in, the wheat stands several centimeters tall. Its major growth comes in the spring and early summer, when precipitation is at a maximum and before the onset of the desiccating winds of summer. It is harvested in late May and June. Today, winter wheat is grown across much of the United States, but its zone of concentration is the southern Plains from northern Texas to southern Nebraska.
Spring wheat - grown primarily from central South Dakota northward into Canada - is planted in early spring and harvested in late summer or fall. It is suited to areas of winters so severe that germinating winter wheat would be killed.
Most grasslands wheat is grown using dry farming techniques, without irrigation. The soil is plowed very deeply to break the sod and slow evaporation. Most visually obvious, especially in the northern Plains, is the widespread use of fallowing, where the land is plowed and tilled but not planted for a season to preserve moisture.
Beginning around June 1 with the winter wheat harvest in Texas, custom combining crews gradually follow the harvest northward. Unlike migrant farm laborers harvesting other crops, these people, often in large crews that use many combines and trucks, have traditionally been well-paid agricultural workers. The farms in most of the "Wheat Belt" now exceed 400 hectares, which means that more wheat farmers can now afford their own combines. Still, probably one-third of all Great Plains wheat is harvested by custom combining crews.
A major problem with profitable wheat production is the difficulty of moving the harvest rapidly to storage in the large grain elevators that dot the Plains. Competition from truck hauling and, in parts of the winter wheat region, barge transport has encouraged the railroads to abandon many small country grain elevators in favor of much larger complexes usually in larger towns. Most export wheat moves through the Great Lakes or in barges down the inland waterway system and the Mississippi River.
Sorghum has emerged as a major crop on the southern Plains in recent decades. Able to withstand dry growing conditions, this African grain now equals winter wheat in importance on the hot, dry southwestern margins of the Plains. Both Texas and Nebraska now have more land in sorghum than in wheat. Most of the grain sorghum crop is used as stock feed.
On the northern Plains, barley and oats are major second crops, with most of the continent's barley crop coming from the Lake Agassiz Basin of North Dakota and Minnesota. Nearly all flaxseed produced in North America also is grown in the northern Plains. Sunflowers, a source of the vegetable oil canola and important ingredients in many livestock feeds, are rapidly increasing in importance in the Red River Valley of Minnesota and North Dakota.
Irrigation in the United States is usually associated with the dry region of the far West. Yet the benefits derived from irrigation may be higher in many semihumid or even humid areas - in terms of the level of increased production per dollar invested - because irrigation water may be used either as a supplement in dry times to maximize yields for crops already grown in the area or to grow crops for which the available moisture is not quite sufficient.
There are a number of Great Plains areas where large-scale irrigation developments are important. Perhaps the most noteworthy of these is on the High Plains from Colorado and Nebraska to Texas. The area is underlain by the Oglala aquifer, a vast underground geologic reservoir under 250,000 square kilometers of the area that contains an estimated 2 billion acre-feet of water. (An acre-foot is the volume of irrigation water that covers 0.4 hectares to a depth of 0.3 meters.) This is "fossil" water, much of it deposited more than a million years ago. About a quarter of the aquifer's area is irrigated, almost entirely with Oglala water. The High Plains is a major agricultural region, providing, for example, two-fifths of America's sorghum, one-sixth of its wheat, and one-quarter of its cotton. Irrigated lands here produce 45 percent more wheat, 70 percent more sorghum, and 135 percent more cotton than neighboring nonirrigated areas. Groundwater withdrawals have more than tripled since 1950, to more than 20 million acre-feet annually.
Early in the 20th century, the area centered on Lubbock, Texas, became a significant region of cotton production. Irrigated farming, using water from wells drilled into the water-bearing sands that underlie much of the southern High Plains, gradually replaced the early dry-farming approach. Today, the region is the most important area of cotton production in the United States. More than 50,000 wells supply irrigation water in the area.
The second major irrigated area on the Plains is in northeastern Colorado, with sugar beets the primary specialty crop. The area has long been irrigated from wells and from the waters of the South Platte River. The federal government covers the cost of construction, and those who use irrigation pay for the water. Because these waters are no longer adequate to meet demands, the government funded the Big Thompson River project, which is designed to carry water from the west slope of the Front Range of the Rocky Mountains to the east slope and the irrigated lands beyond. The most striking technological feature of this project is a 33-kilometer tunnel, lying 1,200 meters below the Continental Divide in Rocky Mountain National Park.
The largest of the water impoundment projects on the Plains is the Missouri Valley project. The project was an outgrowth of two different sets of needs. People living at the lower end of the Mississippi Valley, including those in Kansas City and St. Louis, needed an effective system of flood control. About 100 centimeters of precipitation falls on this area each year. In contrast, people in the upper Missouri Valley, especially the Dakotas and Montana, needed a system to provide ample water for irrigation. The resultant system is composed of a series of large earth-fill dams on the upper Missouri, as well as numerous dams on many of the tributaries of the river.
These and many other smaller irrigation projects and individual wells have allowed a great expansion in the diversity of Plains agriculture. Throughout the central and northern Plains, alfalfa - the premier hay crop of the West - claims the largest irrigated hectarage. Sugar beets are important in the Arkansas River Valley of eastern Colorado and western Kansas, and along the South Platte in northeastern Colorado. Arkansas valley growers also take great pride in the quality of their cantaloupes, while corn, usually irrigated from wells, is a major crop in south-central Nebraska.
The sediments of the Great Plains contain major reserves of energy resources - petroleum, natural gas, and coal. To the south, major petroleum and natural gas fields are traditionally among America's leading suppliers of these products. The Panhandle Field, encompassing western portions of Texas, Oklahoma, and Kansas, is the world's leading supplier of natural gas. The same three states are major petroleum producers, and recent developments have also added Wyoming to this group.
North Dakota can boast of sizable energy resources, mostly in the form of soft coal, but it is Wyoming that is the leading coal-producing state in the United States. In 1996, Wyoming mines provided 26 percent of the total U.S. coal output, or 1.06 billion tons.
Denver has become a focus of considerable petroleum-based wealth. Alliance, Nebraska, nearly doubled in size between 1975 and 1980 because of its location on the Burlington and Northern rail line, which carries coal eastward from the Wyoming fields. Gillette, the largest town in the center of Wyoming mining activity in the Powder River basin, saw its population increase by a factor of five in a decade.
The passage of the Clean Air Act in the United States in the early 1970s provided an important boost for the West's generally low-sulphur coal. At least 100 billion tons of low-sulfur sub-bituminous coal that meets strict antipollution laws can be found near the surface in the Northern Plains, an amount equivalent to that needed for 125 years at current levels of national consumption. Within 2,000 meters of the surface, the total is perhaps 1.5 trillion tons. Already the structure of the regional economy is shifting, with agriculture and ranching declining in importance.
Population decline, or at best stagnation, has become the accepted standard across much of the Great Plains during the past 50 years. The region has a decided lack of urban centers, major recreational potential is minimal, and, until recently, there were few important natural resource developments. Regional population growth is concentrated in the larger cities near the margins of the Plains, while most smaller communities and rural areas experience outmigration and often population decline.
Much of the region is served by major urban centers that are found somewhat beyond the peripheries of the Plains. Chief among these are Kansas City (Missouri) and Minneapolis-St. Paul (Minnesota). Denver (Colorado), Dallas-Fort Worth (Texas), and San Antonio (Texas), the largest American cities on the Plains, are all peripheral. Denver is a regional office center as well as the focus of financial activity for energy resource development on the Northern Plains and in the Interior West. Dallas, also a dominant regional office center for the Southwest, seems more of a city of the humid east, whereas the smaller Fort Worth - 50 kilometers to the west - is a ranching and stockyard center that is clearly part of the Plains. San Antonio is the largest commercial center in south Texas plus the home of several major military bases.
Many of the somewhat smaller centers serving the area are also peripheral - cities such as Tulsa (Oklahoma) and Omaha (Nebraska). The service areas of the cities grouped around the edges of the Plains tend to be elongated east-west zones that cover the region.
Most towns on the Plains began as transportation centers, commonly strung out along the railroads. Those that have prospered maintain some transport service function, but they have also become established regional market centers. Some are also supported by special local conditions - Oklahoma City and Tulsa, for example, are important petroleum centers. Wichita, Kansas, is a manufacturing center for small aircraft.
The beef processing industry has expanded into many smaller Plains communities during the last three decades. Formerly, the industry had been concentrated in the Midwest, where facilities were large and complex. Changing technology in the slaughter industry, the growth of feedlots on the Plains, and more diversified marketing patterns gradually made smaller plants located near the new feedlots of smaller Plains towns more economical.
Transportation routes on the Plains were originally built to cross the area rather than to serve it. Thus, most major highways and railroads pass east-west across the Plains, with few lines running north-south.