copyright Alan A. Lew, 2004, all rights reserved


Great Plains Virtual Field Trip

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  • Physical Geography
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    Physical Geography of the Great Plains

    Location and Boundaries

    The Great Plains are located between the South and Midwest regions to the east and the Rocky Mountains to the west. While the Rockies rise to form a well-defined western boundary, the eastern boundary of the Great Plains is not so clearly marked. As with the Midwest, the Great Plains region is located entirely within the Interior Lowlands of North America, extending from Texas into Canada.

    Sloping Sedimentary Rock

    The Great Plains region is often described as having the most homogeneous (and monotonous) topography of any part of the US. The underlying rock structure is primarily composed of sedimentary rock, which gradually increases in elevation to the west. The elevation of Denver, located on the Great Plains at the foot of the Rockies, is 5,280 feet (one mile) high. The sedimentary layers were formed by outwash, from the rising Rocky Mountains to the west, filling in the vast inland sea that once lay between the Rockies and the Appalachian Mountains.


    US Elevation Map (green = lowest elevations; brown = highest elevations)

    The High Plains and the Ogallala Aquifer

    The largest section of the Great Plains is known as the "High Plains" and stretches from the Llanos Estacado (or "Staked Plains" - located in west Texas and eastern New Mexico) to southern Nebraska. The High Plains are a very thick layer of sedimentary rock with deep and broad valleys cut by dispersed rivers. Underlying the eastern portion of the High Plains is the Ogallala Aquifer. This aquifer is estimated to hold as much water as Lake Huron and is a major source of well irrigation water for agriculture.


    Lake Agassiz Basin/Red River Valley

    Extending into Canada in the north is the Lake Agassiz Basin (aka Red River Valley). Lake Agassiz was once the largest lake on the North American continent. It was bigger than all of the Great Lakes combined and was created by glaciers damming the Red River and preventing it from flowing into Hudson Bay. The old lake bed is very flat, containing rich alluvial soils deposited by the lake, and is a major wheat-growing area.

    Red River Basin Map


    The Black Hills of SD

    The Black Hills* are located mostly in South Dakota but also extend into Wyoming. Along with the Bighorn Mountains in Wyoming, they are an outlier of the Rocky Mountain system. Unlike the surrounding sedimentary rock, both mountain areas are composed of metamorphic and igneous rock. The Black Hills also contain the most productive gold mine in the US, although with sites such as Mount Rushmore, tourism and recreation form the basis of the area's economy today.

    The Sand Hills of Nebraska

    The Sand Hills of central Nebraska form the largest sand dunes area in the Western Hemisphere. Like many features in the northern US, the Sand Hills were formed at the southern edge of a large glacier, where sand particles scraped from farther northward were deposited. The dunes today are held in place mostly by grass cover.

    The Badlands of SD

    Badlands are areas where very deep erosion has occurred in the sedimentary rock. Steep towers and cliffs with little vegetation characterize these landscapes, which are scattered between the Black Hills and the Missouri River in South Dakota. They often indicate areas that were not covered by glaciers in past ice ages.

    Climate Extremes

    The Great Plains experiences the greatest extremes in temperature and climatic conditions of any region in the US. Winters are cold, with frequent snowy blizzards, while summers bring hot, dry winds. As in the Midwest, temperature extremes increase northward. Texas towns typically experience a 50-degree F difference between average January and July temperatures. In northern North Dakota, these difference reach 70 degrees F.

    Hail Storms and Blizzards

    Every year, hail storms on the Great Plains destroy millions of dollars of crops. Their occurrence is most frequent in the westernmost portion of the Great Plains. Blizzards are caused by thrusts of extremely cold polar air moving across the Great Plains. This air brings high winds, intense cold, and heavy snows lasting for several days at a time.


    The Great Plains also experience more tornadoes than any other region in the US. These 200+ mph whirlwinds occur throughout the middle and lower plains, centered on the state of Oklahoma. From the late spring and into summer, the Great Plains also experience the fastest nontornado winds in the US. These warm winds cause high rates of evapotranspiration, limiting the useability of the region's limited rainfall.

    Tornado Counts by County


    Satellite Image showing the path of destruction made by a tornado in Oklahoma (the light colored diagonal line across the image)


    Unpredictable Precipitation

    Like the Midwest and South, most of the moisture falling on the Great Plains comes from the Gulf of Mexico in the summer months. As the winds rise up the Mississippi River Valley, they curve slightly westward and then back to the east toward the Midwest. At the same time, Pacific Ocean winds from the west are sapped of their moisture as they rise over the Rockies, creating a rainshadow over the Great Plains. The result is a very unpredictable and unreliable annual rain.

    Dust Bowl Cycles

    When the region was first being settled in the late 1800s, periods of good rainfall would attract large numbers of settlers. Then several years of drought would occur, causing economic recessions and turning fields into dry wastelands. This happened several times in the 1800s and early 1900s, with the worst dust bowls occurring in the depression years of the 1930s.


    The average rainfall in the central part of the Great Plains is 20 inches/year. Any one place, however, typically experiences between 80% (16 inches) and 120% (24 inches) of its average. It is considered a drought condition when rainfall reaches no more than 80% of normal for a year. Major droughts occur approximately every 20 years (1890s, 1910s, 1930s, 1950s, and 1970s). The 1990s have witnessed yet another period of serious drought conditions, especially in the southern Great Plains where hundreds of millions of dollars in agricultural crop production has been lost due to some of the hottest and driest conditions that the region has ever experienced.


    Click Here to See a Map of Current Drought Conditions in the US*


    Wet and Dry Grasses

    The natural vegetation on the Great Plains is grass. A rainfall average of 16 inches/year generally results in drier, short grasslands (steppe climate). A rainfall average of 24 inches/year generally results in taller (1-3 foot) grasses (sometimes known as "prairies" ). The line separating the short and tall grasses is located where an average 20 inches of rain falls each year. This line is located at 98 degrees west longitude and runs through the center of most of the Great Plains states: North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas. (By comparison, the annual average rainfall for the Gulf Coast is 50 inches; for the South, 40 inches; and, for the Midwest, 30 inches.)

    Both the tall and short grasses develop a deep network of roots (known as "sod") in order to extract the maximum amount of water from the soil. The early settlers in the Great Plains were referred to as "sodbusters," because it would sometimes take as many as 20 animals pulling a single plow to break the sod.

    US Vegetation map (not very clear, but does show general differences in color)



    Midwest Vegetation - Trees - Grasses - Shrubs



    US Vegetation Triangle

    US Grass Cover map


    US Prairie Region map


    98 Degrees West Longitude

    Note that many people also refer to this dividing line as being at 100 degrees west longitude. The difference between 98 and 100 degrees is not significant.

    Agriculture East and West of 98 Degrees West Longitude

    As mentioned, the line of 98 degrees west longitude divides areas receiving greater than and less than 20 inches of rain a year, and the tall grasses areas (to the east) from the short grasslands (to the west). This line of longitude also separates areas of crop (wheat, corn, and oats) and mixed (crop and livestock) farming to the east, and mostly livestock (cattle and sheep) and scattered irrigated agriculture to the west.

    US Precipitation


    US Precipitation by County Map~

    US % Agricultural land


    Settlement East and West of 98 Degrees West Longitude

    The 98-degree west longitude line also divides areas where the US population density is more than 20 persons per square mile (east) and under 20 persons per square mile (west). Related to this, the transportation network (road system) is much more dense to the east than to the west. Most of the major transportation routes cross the Great Plains in an east-west direction. They are primarily designed to cross the region, not provide access to the scattered settlements within it. Rail lines go only east-west, while the only north-south interstate freeways are located on the eastern and western edges of the Great Plains.

    US Highway System Map


    East-West Zones of Urban Influence

    The transportation system both responds to and enhances the development of east-west functional regions. Minneapolis dominates the northern Great Plains in trade, finance, news, and professional sports. Dallas dominates the southern areas, while Denver, Chicago, and Kansas City divide up the middle.


    Other East-West Differences

    The 98-degree west longitude line also separates the Central and Mountain Time Zones and even influences the religious geography of the US. Generally (there are many exceptions), most of the major Protestant areas in the US are located to the east of this line, while the west is predominantly Catholic.'s 100th Merdian information page*

    100th Meridian Initiative* - about the spread of the zebra mussle -- only peripherally about the 100th meridian

    Settlement Geography of the Great Plains

    The Plains Indians

    The Plains Indians were the earliest settlers on the Great Plains. They traditionally lived in small groups scattered in semi-permanent settlements along the dispersed streams in the region. They often migrated following the large bison (American buffalo) herds that roamed the Plains.

    Spanish Horses

    When the Spanish explorers arrived in the 1600s, they brought and left a few horses, which also thrived in the Plains environment. By the time the first Americans arrived from the East Coast in the 1800s, the horse had become widely adopted by the Plains Indians.

    Nineteenth-Century Population Pressures in the East

    As nineteenth-century population pressures increased in the east, European-American settlers increasingly came into conflict with native tribes. This was especially true in the South, where many of the soldiers who fought in the Revolutionary War were given Indian land instead of the salary they were entitled to.

    1832 Indian Removal Bill

    In 1832, President Andrew Jackson signed the Indian Removal Bill, which called for the forced removal of all Indians from the Southern states to lands west of the Mississippi River. Most of the removed tribes were settled in Oklahoma. (Native Americans were not considered US citizens; however, the US Supreme Court had declared in 1831 that the federal government must protect their rights under the US Constitution. White settlers openly took Indian lands in the east. President Jackson refused to enforce any laws protecting Indian rights, thereby engaging in a legally impeachable offense.)

    Indian Removal map


    Trail of Tears route map~


    Spanish and American Interests in the "Great American Desert"

    Northern Europeans initially referred to the Great Plains as the "Great American Desert." To them, the environment was an alien one in which they saw no potential value. However, the Great Plains very much resembled the grasslands of central Spain. The Spanish concentrated on building their empire in central Mexico and only started arriving in large numbers on the southern Great Plains at about the same time as the Americans from the East Coast. Conflicts between the two groups eventually led to Mexico's loss of Texas, California, and all of the area between these two states.

    Americans in Mexican Texas

    In 1821, Mexico gained independence from Spain. Americans from the South began moving into the east TX portion of Mexico in the 1820s because of its excellent conditions for growing cotton. By 1830, there were 20,000 Americans and 2,000 slaves living in Mexican Texas. The American settlers spoke no Spanish, held no loyalties to the Mexican government, disregarded Mexico's abolition of slavery, and demanded increasingly greater autonomy within Mexico. After a year of sporadic fighting, the Battle of the Alamo* was fought in 1836, in which 6,000 Mexican troops defeated 187 Americans and Europeans in a lengthy battle. In that same year, the Americans in Texas declared their independence and soundly defeated the Mexican forces.

    Texas Statehood

    Texas sought immediate acceptance as a state of the US, but were rebuffed by President Andrew Jackson, who did not want to upset the Mexican government. For nine years, Texas was a separate country, with increasingly closer diplomatic ties to England. Fearing British influence, the US annexed Texas in 1845, which was one of the factors leading to the Mexican-American War. Unlike any of the other 49 states, however, Texas was not required to turn over all of its public land to the federal government on statehood. This was very unusual, especially for a western state. In return, however, the state was responsible for paying back all of the international debts it had incurred as an independent republic without federal aid.

    Innovations That Enabled Settlement of the Great Plains

    It took the early eastern settlers some time to adjust to the Great Plains environment. There were no trees to build houses with, water sources were scarce, and rainfall was unpredictable. Several nineteenth-century innovations changed this situation. Barbed wire replaced scarce wood for fencing; windmills enabled water to be pumped from wells much deeper than those in the East; and the first rail lines brought wood from the East to replace sod for house building.

    "Winter wheat" was brought by Russian Mennonite immigrants and proved well adapted to the fluctuating conditions on the Great Plains. These immigrants (many of whom originally migrated to Russia to escape religious persecution in Germany), came from the Ukraine, which has similar physical geography conditions to the Great Plains.

    John Deere introduced the steel plow in 1882, making it much easier to break the dense sod soils. This, along with other advances in the mechanization of agriculture, allowed a single farmer to work larger areas of land, thereby compensating for lower productivity per acre.

    The Homestead Act of 1862

    The Homestead Act of 1862 was also instrumental in encouraging settlement of the Great Plains. The act, designed to speed up the settlement of the rapidly growing US, provided 160 acres at a nominal cost to any head of a household who was over 21 years old and who would live and work on the land for five years. (Alternatively, the land could be bought after six months at $1.25 an acre. The land could not be sold or given away to pay an existing debt.) Later, the act was modified to allow the acquisition of more manageable 40-acre parcels.

    Oklahoma Taken from the Indians

    The Native Americans who were removed from the East to Oklahoma in 1831 were promised the rights to their new lands "for as long as the sun shines, the rivers flow, and the grass grows." Many of the Plains Indians were also relocated to reservations in either Oklahoma or South Dakota. Gradually, more and more homesteaders made their way westward, settling the areas around Oklahoma. Because good homesteading land was becoming increasingly scarce, President McKinley, in 1889, voided the treaties establishing the Oklahoma reservations and opened the lands to non-Indian settlement. (Native Americans commemorated the 100-year anniversary of this event in the summer of 1989, declaring it to be the greatest single betrayal ever perpetrated against Indians by the US government.)

    Map of Indian Battles in latter 1800s* (large 160k file)

    The Spanish Introduction of Ranching

    The entire approach to cattle ranching in the American West actually originated on the plains of Spain, where climate and geology is quite similar to that of the Great Plains. Cattle ranching on the Great Plains was first introduced into south Texas by Spanish migrating up from what is today Mexico. Ranching was rapidly adopted across the Plains, reaching all the way to Canada by the mid-1800s.

    Post-Civil War Cattle Boom

    During the Civil War, millions of cattle ran free and unmarked across the Great Plains. After the war, these cattle formed the basis for new, and even larger, ranching operations to feed the growing industrial cities of the Northeast. Herds of cattle were driven across the Plains to the newly constructed transcontinental railroad lines, also built after the Civil War.

    The Open Range

    In the early years, cattle grazed on the "open range," meaning there were no fences. By the 1880s, the open range was rapidly disappearing due to overgrazing and increasing competition for land from sodbusters. Open range ranching was pushed farther and farther westward, until it completely disappeared.

    Modern Agriculture on the Great Plains

    Only limited ranching is practiced on the Great Plains today due to competition from Midwest pen-fed beef and greater returns from grain production. Modern agriculture on the Plains is characteristically large scale (much larger than in the Midwest), machinery intensive, and dominated by wheat production.

    Winter Wheat

    Winter wheat is grown in the central Great Plains from Texas to Nebraska. It is planted in the fall, grows several inches, becomes dormant in the winter, grows again in the spring, and is harvested in the summer. This allows it to receive plenty of moisture before the parching summer winds arrive.

    Spring Wheat

    Spring wheat is grown in the northern Plains. It is planted in the early spring and harvested in the fall. The cooler summers in the north allow it to thrive through the humid summers. Kansas (with winter wheat) and North Dakota (with spring wheat) are the largest wheat-producing states in the US. Other important grain crops grown on the Great Plains include barley and oats in the north and sorghum (used for animal feed) in the south.

    USDA Crop Maps* - most recent US government data

    Economic Difficulties

    Because the Great Plains border the South and Midwest in a broad transition zone, it also shares some of the problems of these two regions. Agricultural land throughout the Plains has declined in value from overpricing in the 1960s and 1970s. The oil-based industries of Texas, Oklahoma, and Colorado have led to serious financial problems in Dallas, Kansas City, and Denver. Even the Sunbelt attractiveness of the southern Plains has not saved farmers, businesses, and banks from economic hardships. By the 1990s, however, the economic shake-out in the region had subsided. There are now fewer small towns and fewer farmers, but a much healthier economy exists for much of the region.

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