Most people believe they enter the Great Plains as they cross into Kansas, Nebraska, and other states along that general longitude. From the geomorphologist's and geographer's viewpoint, the Great Plains is arbitrarily set further west in these states, where lowlands elevations begin to rise to their maximum ascension at the Rocky Mountain Front. This map helps to place the Great Plains physiographic province in context with the rest of the U.S.
Say "Great Plains" and typically the first thought is agriculture - this region is often called the "Bread Basket of the U.S." because wheat is the dominant crop. While that is valid, the Great Plains can also be thought of as transitional from the vegetation-dominated eastern half of the U.S. to the rock- and soil-dominated western half. Consider this AVHRR scene that shows almost all of Kansas.
The state's land cover falls roughly into three parts: 1) Eastern (olive): a mix of forests and fields; 2) Central (blue): mostly farmlands; and 3) Western (green): a mix of farms and grasslands, vegetation becoming semi-arid, as elevations rise.
Here is an ASTER image that shows an area of the Great Plains almost totally occupied by farmlands:
Another mental picture of the Great Plains is that of natural (wild) grasslands which are almost synonimous with the term "prairie", such as depicted here:
So, as our journey continues to the west, the terrain slowly rises in elevation and local hilly surfaces, often with low scarps, begin to appear. This Landsat-1 image is typical of the farmlands in central Kansas. This August. 1973 scene shows fields that contained now harvested winter wheat in blue and spring wheat and other crops such as alfalfa in red. The area contains mostly Tertiary sedimentary rocks. Much of the water is obtained from the vast underground aquifer known as the Ogallala formation (it is being rapidly depleted by overwithdrawal).
In this next scene, acquired in October, 1972, we are now over the Great Plains of southwestern Kansas. During fall and winter, the ground has a grayish-brown look that intensifies even further to the west in Colorado. This is also evident in parts of this scene, wherever farm crops have not blotted out their underlying soils (i.e., fields currently fallow), or the natural surfaces are not converted to agriculture. An example occurs in the lower left corner where the Cimarron River has developed gullied badlands (dendritic drainage) in soft sediments. Note that many farms are square and are often just one mile on a side. These squares correspond to the section divisions in the Township-Range system of land mapping that was adopted in the 19th century in the United States. Near the upper right corner are clusters of circular pivot-irrigation fields, similar to those we showed on page 3-3. These fields lie along the Arkansas River just to the west of the largest town in this part of the state, Garden City.
A Landsat TM image within which is Garden City, Kansas is another typical view of Great Plains farmlands. The time is early Spring when some crops (in red; probably spring wheat) are ready for harvest, other farms remain fallow before planting. The green areas (not a natural color in this false color rendition) are mainly grasslands.
As a generalization, the Great Plains scenes appear similar to some western Interior Lowlands scenes, both of which, are dominated by farmland. On the ground, the Kansas landscape has a more western look because of the semi-desert vegetation, including grasses and sage-like shrubs. There is more red in the eastern (right) half of the image than to the west, because of differences in crop type and stage. That is, wheat is more common in the western part of the image, and according to the harvesting schedule, the higher and somewhat cooler western lands had been culled earlier in the Fall.
There are few large cities in the Great Plains. Exceptions are Dallas-Fort Worth, which we examined in Section 4, and Kansas City, MO and Omaha, Nebraska which lie near the boundary between the eastern Great Plains and the Interior Lowlands. Here is a color photograph of Omaha, with Council Bluffs, Iowa across the Missouri River, taken by astronauts onboard the International Space Station:
The two largest cities in Oklahoma appear in this next Landsat-1 image. Tulsa is the blue patch in the upper right; Oklahoma City is much harder to see in the lower left. Both oil and agriculture are important in this region, where trees are still fairly common, although giving way on the west side to more western Great Plains vegetation (brush; grasses).
Here is a satellite image that shows Tulsa, Oklahoma:
Where the western Great Plains extends into Canada, a visually striking difference marks the exact border between that country and the U.S., clearly evident in the scene below. The lower half lies within the farmlands (mostly wheat) of eastern Montana (note the elongate shapes of many farms). But across the border in Alberta, Canadian settlers chose to retain the natural vegetation (grasslands) and devote this land use to grazing of cattle (some farms are seen in the upper right). On the U.S. side, the plains surround two older outliers of igneous rocks, the Bearpaw Mountains (lower right) and the Sweet Grass Hills (center left), both forested.
Plains terrain can be modified into badlands and gullies, as seen in this image of western North Dakota near the Montana border:
Most of the northern Interior Lowlands has its topography, vegetation, farm crops, and landscape developed on drifts and tills deposited during the Pleistocene glaciation. The Great Plains in this Landsat-1 scene (in mid-May when vegetation is just emerging) is relatively flat as the overlying till plains is not dissected. Parts of Saskatchewan, Manitoba, and North Dakota are within the scene. However, the Turtle Mountains (elliptical feature) are actually a dissected mesa (of Eocene sandstones) rising about 210 m (700 ft) above the surrounding plains; these wooded mountains were glaciated and have many lakes, making this a popular vacation areas:
When one thinks of the northern Great Plains, the two Dakotas (North and South) come to mind. Both states actually have their eastern land in the Interior Lowlands but our mental picture sees them as more like the Great Plains. The largest city in North Dakota, Fargo (about 100000), is just west of the Minnesota line;
The northern Great Plains has been experiencing a drought of late. The Oahe Reservoir (some 325 km long), normally the fourth largest in the U.S., has lost much of its water as evident in the ASTER image on the right:
It is surprising to some, especially after flying over the Interior and Great Plains, that the region from a broader perspective is not flat but often displays rolling terrain and distinct valleys. This is dramatically revealed in this next portrayal - a Heat Capacity Mapping Mission (HCMM; see page 9-8) Nightime Thermal Infrared view of nearly all of northern Kansas, most of Nebraska, and the southwest corner of Iowa. The Missouri (top) and Platte (center) Rivers control the major drainage. The sense of relief is brought about by the tendency of cooler air (darker) to sink into lower terrain at night, producing an effect somewhat like a shaded relief map.
The Great Plains, which grades eastward into the Interior Plains, has a variety of landscapes, including areas that have few farms. A typical example of a more diverse scene appears below. Most of the July 4, 1973 Landsat image is in western South Dakota. On the upper left is a portion of the Black Hills, which rise several thousand feet above the rolling terrain whose elevation exceeds 4000 ft (1100 meters). The Black Hills, home of Mount Rushmore and the Homestake Mines in Deadwood, S.D., are a broad domal uplift exposing igneous and metamorphic rocks over most of the interior. Geologists consider the Black Hills to be an offshoot of the Rocky Mountains, which we will encounter on the next page. The Sand Hills of Nebraska are in the lower right.
At the lower right corner of the Landsat MSS image (above) is the northwest end of the Sand Hills of Nebraska whose dune fields are discernible. The Sand Hills are one of the largest dune fields in the Western Hemisphere. They formed some 10000 years ago by strong winds in the early post-glacial phase of the last major glaciation. Sand is the interior material in the longitudinal dunes that are capped by loess (fine-grained silt) which allows some vegetation to grow on the dunes themselves. Water is trapped between dunes to form lakes (some evaporate periodically). We show the western 2/3rds of the dune field in this May 15, 1973 Landsat MSS image (Band 5); the main river is the North Platte, the large water body built by damming this river is Lake McConaughy. A ground photo shows typical landscape within the Hills.
Different impressions of this largest sand dune field east of the Rocky Mountains are given by the next three illustrations: the first, a Terra satellite close-up, the second an aerial view in late winter, and the third a ground scene.
Almost due north is the famous Badlands (bluish-white), an extensively gullied area cut by erosion into soft, easily eroded, often colorful, Tertiary sediments (see figure below). The medium-blue-gray areas are weakly dissected plains with sparse vegetation. This High Plains Tablelands is bounded on its southeast by the forested Pine Ridge escarpment. This Terra satellite view shows more details within the Badlands.
A significant anomaly in the western Great Plains are the Black Hills of South Dakota. This rises to elevations in excess of 2700 meters (8000 ft). They are actually an extension of the Rocky Mountains. They appear green in this Landsat image.
Here is a perspective view looking west at the eastern side of the Black Hills, made from Landsat and DEM data.
The reason that the Black Hills got its name is its general "darkness" owing to a preponderance of dark pine species. This is quite apparent in this Landsat-1 false color image of the Black Hills during wintertime when snow blankets the surrounding plains with snow, which is not visible within the Black Hills because the evergreen canopy prevents its exposure:
This aerial view shows the main reason for the Black Hills being dark, namely, because most of its vegetation consists of evergreen fir trees:
However, nowadays, in the mood of patriotism brought on by 9/11 and Iraq, the Black Hills have taken on a center stage position as we look back to our roots. On the side of a granite mountain south of Rapid City is the famed rock sculptures of the faces of George Washington, Thomas Jefferson, Teddy Roosevelt, and Abraham Lincoln - the Mount Rushmore Memorial - a National Monument.
Compare this last image with a ground photo taken through a telescopic lens:
Incidentally, some have questioned the inclusion of Teddy Roosevelt in this quartet. Read his life: perhaps he's not among the greatest (but high up), but few would dispute he is probably the most interesting President owing to his "free spirit" personality.
Off the northwest end of the Black Hills is the famed Devils Tower (it was a centerpiece theme in the movie "Close Encounters of the Third Kind"). Devils Tower is actually the exposed central vent of a volcano, with the enclosing volcanic beds having been stripped away by erosion. The volcanic rock is conspicuously marked by "fluting", that is, shrinkage joints produced during cooling of the solidified lava. In the aerial photo below, it is hard to pick out the top of the Tower, but its presence is indicated by its shadow. The Tower (pictured beneath) is nearly flat (it was a popular target for skydiver parachutists until the National Park Service began to arrest the divers [it became a real nuisance to have to have Ranger climbers rescue the divers from the top]).
Lets move off flightline to look at some images from various areas in Texas. This is the largest of the 48 states. Its environmental niches range from pinewoods and deciduous forests in the east through grasslands in the center to desert landscapes in its west. This composite of images made by the NOAA-14 satellite shows the entire state and surroundings (including northeast Mexico):
Now look at parts of the Great Plains in Texas. The first image is of the Llano Estacado (Staked Plains) in the Panhandle of Texas. The bluish area locates Lubbock, TX. The Ogallala formation (Miocene in age) is capped by up to 10 m of caliche (calcium carbonate formed by precipitation from upwelling groundwater) and is responsible for the low plateau (in brown) which supports mesquite brushland. The yellowish areas are mainly undeveloped grasslands. Some oil fields - an offshoot of the West Texas petroleum deposits - are present in the scene.
The southernmost section of the Great Plains is the Edwards Plateau in central Texas. Cretaceous Limestones are the dominant rock type. These have been downcut by stream and wind erosion to form canyonlands and gullys in a region of low relief; elevations in this scene range from 600 to 900 m (2000-3000 ft). This is cattle and sheep country rather than farmland. Vegetation is mostly scrub savannah with Junipers and Live Oaks. At the bottom is the Amistead Reservoir formed by damming the Rio Grande. The Pecos River joins it as that river moves south-southeast. Note the canyonland near the left edge of the image.
In the flatlands just south of the Edwards Plateau lies the city of San Antonio.
In the upper left is the forested edge of the Edwards Plateau, bounded by the Balcones Escarpment. Below is a major attraction in San Antonio - the popular River Walk - restaurants and shops along the small Salado River that flows through the town.
The next scene is not in the Great Plains as such but is topographically and ecologically similar to parts of the southern Great Plains in Texas. The region here lies in the Texas Coastal Plains, built up, as is nearly all the Coastal Plains province running from the southern U.S. to New Jersey, of Miocene to Pleistocene sedimenary rocks deposited when sea level was higher during marine invasion onto the continent. Corpus Christi (near top center) is found along the mainland side of its Bay. Just north of Corpus Christi is Aransas Pass - winter home of the endangered Whooping Crane. Almost the entire Texas coastline is one continuous string of barrier islands, with lagoons and the Intracoastal Waterway to on their landward side. Best known is Padre Island (bottom to near top), a National Seashore preserve which runs nearly the entire length of this scene. A vast amount of the land south of Corpus Christi was once a huge cattle grazing endeavor, the famed King Ranch, which still exists but has shrunk by sale of some of its holdings.
The NOAA image of Texas, shown above, offers evidence of the more western "flavor" of the state as one moves from San Antonio to the west. This next Landsat-1 scene shows the land around the Big Bend National Park in West Texas; small block fault mountains and volcanic terrain are conspicuous; the Rio Grande is a narrow stream running through the image:
Parts of the Big Bend country are volcanic. The region has perhaps the most rugged scenery in Texas:
This is typical west Texas landscape:
True desert marks the westernmost end of Texas at El Paso, seen in this ASTER image (its Mexican counterpart, Juarez, lies just south of the Rio Grande). El Paso has a population of 775000 while Juarez is up to 1,500,000 people.
Rather mysteriously, in this astronaut photo taken at night, the areal extent of Juarez seems much greater than that of El Paso. A speculation, Juarez has a more active nightlife and thus is lit up in this late night image:
As the western Great Plains approaches the Rocky Mountains, the topography develops gullies (draws), canyons, and a few mesas or plateaus because of increased downward erosion resulting from the higher elevations. Farms diminish rapidly westward and a semi-desert vegetation cover gives hints of true Western U.S. ecosystems, as seen in this image of Southeast Colorado: