Chapter 28
Ecological Subregions of the United States

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Prairie Parkland (Temperate)

Seven Sections have been delineated in this Province:

These Sections are located in the north-central conterminous States, including parts of Oklahoma, Kansas, Nebraska, Missouri, Illinois, Indiana, Iowa, Minnesota, and North and South Dakota. The area of these Section is about 218,200 mi2 (565,100 km2).

Section 251A--Red River Valley

Geomorphology. This Section is part of the Central Lowland geomorphic province. It forms the southern extension of a large, level lacustrine plain (Glacial Lake Agassiz) that extends far to the north and west into Manitoba, Saskatchewan, and Alberta. The plain is bisected by the Red River valley. Prominent alluvial fans formed where the Pembrina and Sheyenne Rivers entered the glacial lake from the west. Beach and morainal ridges border the Section on the east. Other features include kettles, wetlands, and dunes adjacent to the fans. Drainage is a modified trellis pattern; tributaries enter the Red River from uplands to the east and west. Geomorphic processes operating in the Section are fluvial erosion, transport and deposition. Elevation ranges from 825 to 1,150 ft (250 to 350 m). Local relief is 3 to 25 ft (1 to 8 m).

Lithology and Stratigraphy. Pleistocene (Wisconsinan) till and lacustrine sand-silt-clay-peat-muck cover bedrock to a depth of 200 to 400 ft (60 to 120 m). Quaternary alluvium covers the lacustrine sediments in the fans and major river valleys. Bedrock is predominently Archean granite, metasediments, and greenstone; Cretaceous shale and minor Jurassic sandstone overlap the Archean on the western and southern margins.

Potential Natural Vegetation. K\"uchler types are bluestem prairie and northern flood plain forest, with the latter mapped in a narrow strip along the Red River and its major tributaries.

Fauna. Historically there were large populations of bison, elk, and antelope. Large predators included the prairie wolf and grizzly bear. (This Section marked the eastern-most range of both the grizzly bear and antelope). Other common species were the prairie chicken, sharptail grouse, prairie dog, and meadow lark. This area supported large numbers of both nesting and migrating waterfowl such as the mallard, pintail, greenwing teal, bluewing teal, and Cinnamon teal, canvasback and redhead ducks, as well as Canada and snow geese. Agriculture now dominates the Section; the major characteristic species are the introduced ringneck pheasant, cottontail rabbit, jack rabbit, coyote, red fox, and a host of species adapted to small grain agriculture. white-tailed deer are very common in the wooded draws and riparian shrublands. The bison, elk, antelope, wolf, and grizzly bear have been extirpated. Prairie chicken, sharptail grouse, and the prairie dog survive only in scattered remnants of suitable habitat. Many of the original waterfowl species have been substantially reduced (pintail, mallard, teal, and canvasback) but others (Canada goose and sandhill crane) are faring well, largely due to waste grain residues in agriculture operations.

Climate. Precipitation averages 18 to 23 in (470 to 580 mm.). About 40 percent occurs during the growing season. Precipitation in winter is almost entirely snow. Mean annual temperature ranges from 36 to 45 oF (2 to 7 oC). The growing season lasts 111 to 136 days.

Surface Water characteristics. Drainage is to the Red River of the north, which dissects the Section, and flows to the north. Drainage network is minimally developed. Streams meander through the level topography. Most wetlands have been ditched and drained for agriculture. Flooding is common in early spring, often intensified by frozen conditions to the north, causing water to back up. There are few lakes; they are most common in the southeast on a till plain. Characteristically they are shallow and perched.

Disturbance Regimes. Fire, drought, and annual flooding are significant. High wind events are also common. Historically, bison grazing and ant activity caused important faunal modifications of vegetation and soils.

Land Use. The dominant land use is farming. Most wetlands have been drained for agriculture.

Cultural Ecology. Humans have occupied the area for at least 10,000 years, adapting their ways of life in a variety of changing environments. Conditions have ranged; from cool, wet, tundra supporting herds of open land grazing animals such as bison and caribou; through a warm, dry, savanna period when availability of water and aquatic resources was drastically altered; to the tall grass prairie of the present. People lived in small, nomadic groups and larger villages, changing their hunting, fishing, and gathering methods as environmental conditions changed, to enable the most efficient resource use. Horticulture has been practiced for about 1,000 years. Within the last 300 years, the near extinction of some species of fur-bearing mammals for the fur trade and cultivation of the land have significantly altered the environment. Today, farming and recreation are the major human activities affecting the ecosystem.

Compiled by Eastern Region and Minnesota Department of Natural Resources.

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Section 251B--North-Central Glaciated Plains

Geomorphology. This Section is part of the Central Lowland geomorphic province. It is mostly level to rolling till plain. A series of low, sub-parallel, south to north and southeast to northwest trending morainal ridges is featured in the northwestern third of the Section. The Coteau des Prairies, a moderately dissected, relatively high plateau with a much thinner till cover, is prominent in the northwestern portion. The Minnesota River's broad valley was created by the Pleistocene draining of Glacial Lake Agassiz. There are scattered lacustrine lowlands and outwash channels as well. Elevation ranges from 750 to 2,000 ft (225 to 600 m). Local relief is generally 20 to 100 ft (6 to 30 m); it is higher in a few localized areas, notably the edge of the Coteau des Prairies.

Lithology and Stratigraphy. Pleistocene till, stratified drift, and lacustrine sand and clay mantle virtually the whole Section, from 30 to 300 ft (9 to 90 m) thick; most is Wisconsinan, but Illinoisan-Kansan covers the southwestern portion. A signifiant part of the area is capped with up to 20 ft (6 m) of Quaternary loess (aeolian silt). Quaternary alluvium fills the valley of the Missouri River and other major drainages. Cretaceous shale, limestone, and sandstone form bedrock across most of the west half of the Section and in isolated outliers farther east. These units lap onto Archean granite and gneiss to the north, and Devonian, Mississippian, and Pennsylvanian limestone and shale to the south. Small but significant outcrops of Proterozoic quartzite occur across the Section, where they cap paleo-topographic high points. The Paleozoic rocks are exposed intermittently in the deeper drainages.

Soil Taxa. Types are mostly Mollisolls, with some Alfisols and Entisols. Temperature regimes are mostly mesic, with some frigid in the north. Moisture regimes are mostly udic, with some aquic and some ustic. Well-drained to moderately well-drained loamy soils formed in gray calcareous till of Des Moines lobe origin are dominant.

Potential Natural Vegetation. K\"uchler type is mapped as almost entirely bluestem prairie, with a narrow corridor of northern flood plain forest along the Minnesota River, and a few fingers of oak-hickory forest along other drainages in the southern part.

Fauna. Historically there were large populations of bison, elk, and antelope. The major large predator was the prairie wolf. Other common species were the prairie chicken, sharptail grouse, prairie dog, and meadow lark. This was "pothole" country -- areas of small, saucer-shaped wetlands. It supported large numbers of both nesting and migrating waterfowl, such as the mallard, pintail, greenwing, bluewing and Cinnamon teal, canvasback, and redhead ducks, as well as Canada and snow geese. Agriculture now dominates the Section; and the major characteristic species are the introduced ringneck pheasant, cottontail rabbit, jack rabbit, coyote, red fox, and a host of species adapted to small grain agriculture and woodlands. white-tailed deer are very common in the wooded draws and riparian shrublands. The gray squirrel is common in woodlands, and recently the wild turkey has substantially increased as a result of re-introductions. The bison, elk, antelope, and wolf have been extirpated. Prairie chicken, sharptail grouse, and the prairie dog survive only in scattered remnants of suitable habitat. Many of the original waterfowl species have been substantially reduced (pintail, mallard, teal, and canvasback) but others (Canada goose and sandhill crane) are faring well, largely due to waste grain residues in agriculture operations.

Climate. Annual precipitation averages 20 to 33 in (500 to 850 mm). About half falls during the growing season. Mean annual temperature is about 40 to 48 oF (5 to 9 oC). The growing season lasts 120 to 160 days

Surface Water Characteristics. Drainage is to the Mississippi via the Minnesota, Big Sioux, Des Moines, and Missouri Rivers. The drainage network is well established in the western part. The eastern part has relatively low frequency of shallow drainages. Natural lakes are rare, except in the Des Moines lobe in the eastern part. Many of these lakes tend to be shallow and perched. Small, saucer-shaped wetlands called prairie potholes were common, especially across the western part of this Section. Most wetlands have been drained for agriculture.

Disturbance Regimes. Historically, fire was the most common natural disturbance. Floods and tornadoes also occurred. Fire suppression has allowed woodlands to develop from what was originally oak openings or brush prairies.

Land Use. Current land use is dominantly agriculture.

Cultural Ecology. Humans have occupied the area for at least 10,000 years, adapting their ways of life in a variety of changing environments. Conditions have ranged; from cool, wet, tundra supporting herds of open land grazing animals such as bison and caribou; through a warm, dry, savanna period when availability of water and aquatic resources was drastically altered; to the tall grass prairie of the present. People lived in small, nomadic groups and larger villages, changing their hunting, fishing, and gathering methods as environmental conditions changed, to enable the most efficient resource use. Horticulture has been practiced for about 1,000 years. Within the last 300 years, the near extinction of some species of fur-bearing mammals for the fur trade and cultivation of the land have significantly altered the environment. Today, farming and recreation are the major human activities affecting the ecosystem.

Compiled by Eastern Region and Minnesota Department of Natural Resources.

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Section 251C--Central Dissected Till Plains

Geomorphology. This is part of the Central Lowland geomorphic province. It is characterized by moderately dissected, glaciated, flat to rolling plains that slope gently toward the Missouri and Mississippi River valleys, which bracket the Section on the west-south and east, respectively. Local relief is 20 to 165 ft (6 to 50 m). A minor anthropogenic landform, strip-mined areas, exhibit hummocky or ridge-swale topography. Drainage is dendritic; current geomorphic processes are fluvial erosion, transport and deposition, and minor mass wasting. Elevation ranges from 600 to 1,500 ft (185 to 450 m).

Lithology and Stratigraphy. Quaternary loess (unconsolidated aeolian silt), as much as 25 ft (8 m) thick and thinning to the east, mantles most uplands. Pleistocene (pre-Illinoisan) till and stratified drift underlie the loess and cover most bedrock up to 300 ft (90 m) deep, thinning to less than 30 ft (9 m) to the east and south. The Mississippi and Missouri floodplains have up to 150 ft (45 m) of unconsolidated Tertiary and Quaternary alluvium (gravel, sand, silt, and clay) overlying bedrock; other river valleys across the Section have somewhat less alluvial fill. Isolated outliers of Cretaceous shale and sandstone occur beneath the drift in the northwestern corner of the Section; Permian sandstone forms bedrock along the western margin; Pennsylvanian shale, limestone, and minor coal underlie most of the Section; and Mississippian, Devonian and Ordovician shale and carbonate form bedrock to the east and south. Bedrock is exposed locally along the deeper drainages and in "windows" eroded through the unconsolidated surficial material.

Soil Taxa. Types are mostly Mollisols, some with claypan, with lesser extent of Alfisols. Moisture regime is mostly udic, with some aquic. Temperature regime is mesic. Minerology is montmorillonitic or mixed. Soils are generally deep, rich, and dark-colored.

Potential Natural Vegetation. K\"uchler vegetation types are mapped as dominantly mosaic of bluestem prairie and oak-hickory forest, with oak-hickory forest along drainageways. An estimated 60 percent of the land surface was bluestem (tall-grass) prairie, with bur oak and white oak savannas interspersed and in transitional areas. Upland forest (white oak-shagbark hickory) occurred on more dissected land, grading into bottomland forests and wet bottomland prairies along rivers.

Fauna. Prairie animals are now uncommon, since fewer than 20 natural prairies remain, all less than 20 acres in size. The major ungulates were bison and elk, which have been extirpated; white-tailed deer and cattle are prevalent today. The major predator is coyote (wolves and cougar were extirpated). Raccoon, badger, skunk, rodents. Open-lands birds like hawks, bobwhite quail, meadowlarks, sparrows, swallows are numerous; there are also savanna and woodland species such as turkey, and warblers. The numbers of prairie chicken, already low, declined recently. Introduced ring-necked pheasant are common. There are moderate numbers of reptiles and amphibians.

Climate. Mean annual precipitation is 30 to 40 in (760 to 1,020 mm). About two-thirds of this amount occurs during the growing season. Most winter precipitation is snow. Mean annual temperature is 50 to 56 oF (10 to 13 oC). The growing season lasts 160 to 180 days.

Surface Water Characteristics. A well developed and integrated dendritic drainage network is carved into the land surface. Natural lakes and ponds are rare or non-existent. Many streams that formerly meandered across broad valleys now are straightened by channelization and silted-in from agricultural run-off. A few bottomland wetlands have been preserved from drainage enterprises.

Disturbance Regimes. Fire and grazing by herds of bison and elk were most important in creation and maintenance of this landscape.

Land Use. Nearly all of this area is used for agriculture. About one-half is tilled crop land; the rest is used for haying or pasture. Tree cover is increasing.

Cultural Ecology. Ten thousand years ago, the river valleys of the Missouri and Mississippi were choked with floods from heavy rainfall and the outwash of northern glaciers. Interglacial periods were marked by dust storms. As the glaciers retreated, the Missouri River and its tributaries became a network of routes for water-traveling people to and from Missouri in any direction. Three thousand years ago there was widespread interaction with groups located along the Tennessee and Lower Mississippi Rivers. Two thousand years ago, people lived in villages located near the mouth of tributary rivers. One thousand years later, Cahokia, a major population center, existed with full-scale agriculture. The Missouri tribe continued agriculture and hunting and gathering until European settlement. Later, use of fire was discouraged to increase forest cover, grassland was converted for agricultural use, and strip mining for coal became prominent.

Compiled by Eastern Region, Missouri Department of Conservation, University of Missouri-Columbia, and Natural Resources Conservation Service.

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Section 251D--Central Till Plains

Geomorphology. This Section is part of the Central Lowlands geomorphic province. It is a level to gently rolling till-plain (glacial ground moraine), with broad bottomlands and associated terraces and meander scars along major river valleys. The plain is overlain by a series of low, undulating ridges (glacial end moraines). Relief along flood plain margins of major rivers and their larger tributaries can exceed 150 ft (45 m). A notable but minor landform is anthropogenic. lands that have been strip-mined exhibit humocky or ridge-swale topography. The dominant geomorphic processes operating in the Section are fluvial erosion, transport and deposition, with minor mass wasting. Elevation ranges from 600 to 1,000 ft (180 to 300 m). Local relief is dominantly 3 to 100 ft (1 to 30 m), but ranges up to 165 ft (50 m) along bedrock bluffs along some major streams.

Lithology and Stratigraphy. Section 251D is almost entirely covered by Pleistocene till and stratified drift up to 400 ft (120 m) thick. The tills are of Kansan, Illinoisan, and Wisconsinan age (oldest to youngest, exposed west to east). Up to 25 ft (8 m) of loess cover till and bedrock on bluffs overlooking the Mississippi's flood plain; the loess thins to the east. Wisconsinan lacustrine deposits (stratified silt, clay, peat, and muck) occur along some rivers and tributaries and between moraines in the northeastern part of the Section. Bedrock beneath the drift is composed of lower Mississippian limestones, shales, and sandstones, well exposed on the uplands between the lower Illinois River and the Mississippi's flood plain, and in the bluffs overlooking the rivers. Silurian and Devonian carbonates crop out along the flood plain margins farther north. Mississippian and Pennsylvanian limestones, siltstones, and sandstones are exposed in erosional "windows" through the till along the Wabash and its major tributaries.

Soil Taxa. Types are mostly Udolls and Aquolls, with mesic temperature regime. Moisture regimes are udic and aquic. Soils tend to have relatively thick surface layers, darkened by decomposed organic matter. They are very productive for acricultural crops.

Potential Natural Community. This area is principally tall grass prairie. variations on the big bluestem-indiangrass-prairie dropseed-switchgrass community; cord grass-sedge-blue jointgrass communities on wet sites; and little bluestem-side oats-grama on drier sites. Forest communities occur along stream valleys. white oak-black oak-shagbark hickory community on slopes, with basswood-sugar maple-elm-ash community on wetter, shaded sites. K\"uchler mapped the area as oak savanna and oak-hickory forest.

Fauna. Elk and bison, once preyed upon by the prairie wolf and coyote, disappeared from the area in the early 1800's. The wolf disappeared from the Section in the late 1860's leaving only the coyote and bobcat to prey upon small mammals such as the masked shrew, meadow vole, and western harvest mouse, which are common here today. Avian species such as the black-capped chickadee, northern harrier, upland sandpiper, long-eared owl, and Henslow's sparrow occupy the forest and grasslands; sora, black-crowned night herons, and the veery are found in the sedge meadows and swamps. The Illinois chorus frog, Kirtland's snake, the Plains leopard frog, and Illinois mud turtle typify present day herptofauna. The yellow perch, striped shiner, silver jaw shiner, quiltback and silver redhorse are found in the major rivers and their tributaries.
Climate. Precipitation averages 29 to 35 in (750 to 900 mm). Two-thirds of this amount falls during the growing season. Temperature averages 46 to 54 oF (8 to 12 oC). The growing season lasts 160 to 180 days.

Surface Water Characteristics. There is a relatively low frequency of shallowly entrenched, slow-flowing, meandering streams. A few small marshes and prairie potholes remain.

Disturbance Regimes. Historically, major natural disturbances were prairie fires and grazing ungulates. Since settlement, most of the wetlands, marshes, and "prairie potholes" have been drained for agriculture, and virtually all prairie habitats have been replaced with row crops or pasture.

Land Use. This is highly productive agricultural land. Current land use is almost entirely agricultural, with associated roads, towns, and villages; minor coal and aggregate mining, and oil and gas production occur.

Cultural Ecology. Prehistoric populations generally occupied the major river valleys; their subsistence and tool technologies relied on forest edge, riparian, aquatic and prairie habitats. Transportation and settlement were largely restricted to the major waterways. Population numbers continued to increase throughout prehistory; the pressure caused the most recent prehistoric (400 to 1450 A.D.) and historic (about 1450 to 1840) Native American groups to expand into the prairie interior. Early 19th century Euro-American settlement was also generally restricted to the major river valleys. Completion of the Illinois-Michigan Canal and the Illinois Central Railroad by the mid-1800's funneled increasing numbers of European immigrants into unsettled areas of the prairie. New technology and innovation enabled settlers to drain the extensive prairie wetlands (remnants of broad, shallow glacial lakes) and bring the black prairie soils into cultivation. This land is some of the most fertile and, therefore, most valuable land in the midwestern farm belt. It is the most densely populated rural region in Illinois, and has the highest per capita income of agricultural areas in the State.

Compiled by Eastern Region and The Nature Conservancy, Illinois Chapter.

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Section 251E--Osage Plains

Geomorphology. This is part of the Central Lowlands geomorphic province. It is characterized by a series of sub parallel, southwestern to northeastern trending, maturely dissected, low cuestas or escarpments separating level to gently rolling plains. Local relief on the cuestas is generally between 100 and 300 ft (30-90 m); on the plains it is less than 100 ft. Elevation ranges from 300 to 1,300 ft (100 to 400 m).

Lithology and Stratigraphy. Quaternary loess and residuum blanket this Section. Bedrock is composed almost entirely of Pennsylvanian shale, coal, limestone, and sandstone; sandstones and cherty limestones support the cuestas. Some Permian shale and limestone occur in the northwestern corner of the Section.

Soil Taxa. This Section has about 70 percent Mollisols, with 20 percent Alfisols in the northeast area bordering the Ozark Highlands Section, and 10 percent Ultisols to the south. Soils have a mesic to thermic temperature regime, a udic or aquic moisture regime, and mixed mineralogy. Soils are moderately fertile but shallow enough to discourage tilling throughout most of the section.

Potential Natural Vegetation. K\"uchler vegetation types are mapped as dominantly mosaic of bluestem prairie and oak-hickory forest, with corridors of oak-hickory forest along drainageways. This section was once 70 percent tall-grass prairie, little bluestem and associates, with groves of post and blackjack oaks. Upland prairie graded into wet bottomland prairie, with sloughs, marshes, and mixed bottomland forest. This forest included silver maple, green ash, cottonwood, pecan, pin oak, and bur oak.

Fauna. Habitat includes relatively large surviving prairie fragments, some over 1,000 acres. Cattle replaced elk and bison (the latter are being re-introduced under domestication). White-tailed deer are abundant. Large predators were extirpated, except for coyote. Birds include hawks, turkey vulture, bobwhite quail, meadowlark, scissor-tailed flycatcher, dickcissel, and sparrows.

Climate. Mean annual precipitation ranges from 35 to 41 in (900 to 1,050 mm). Snow averages about 5 in (120 mm). Mean annual temperature ranges from 55 to 63 oF (13 to 17 oC). The growing season lasts 190 to 235 days.

Surface Water Characteristics. This Section has a moderate density of small to medium size, highly meandering, perennial and intermittent streams with dendritic drainage pattern. Most streams have a low to moderate rate of flow and moderate velocity. Large seasonal fluctuations in discharge of streams; i.e., June's maximum may be six times greater than December's minimum. Waters may stand for three months or longer in wide, flat floodplains. There are a few oxbows; some large rivers have been dammed to create reservoirs.

Disturbance Regimes. Fire, grazing, drought (occasionally very severe), and tornadoes were the principal prehistoric sources of disturbance. Coal is strip-mined in many places.

Land Use. Cattle production is a common use. Native vegetation has been converted to fescue pasture and agricultural crops on about 75 percent of the area.

Cultural Ecology. Glacial dust blown from the north enriched valley soils, supporting a thick blanket of vegetation. By 10,000 years ago, small, mobile groups of humans populated the area. Seven thousand years ago, these groups continued hunting smaller game and gathering a wider variety of plant resources. One thousand years ago, the residents settled down to grow crops and hunt buffalo. Slash-and-burn agriculture was practiced. This pattern continued until the arrival of European-Americans.

Compiled by Eastern Region, Missouri Department of Conservation, University of Missouri-Columbia, and Natural Resources Conservation Service.

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Section 251F--Flint Hills

Geomorphology. Relatively old episodes of Paleozoic platform sedimentation were followed by uplift and dissection, characteristic of geomorphic processes historically active in this Section. Present geomorphic processes include gentle and moderate gradient valley stream erosion, transport and deposition. Gentle sloping hills with relief of 300 to 500 ft, found among lowlands, make up most of the area. This Section is within the Central Lowlands geomorphic physical province. Elevation ranges from 985 to 1,970 ft (300 to 600 m).

Lithology and Stratigraphy. Most of the Section is interbedded Pennsylvanian carbonates and shales with recent alluvium in the major river valleys. The northeastern quarter of the Section is Quaternary glacial till, lacustrine, and fluvial deposits.

Soil Taxa. Types include mostly Mollisols, with 20 percent in Inceptisols along hilly terrain in the southeastern area of the Section. Soils have a mesic or thermic temperature regimes, a ustic moisture regime, and mixed mineralogy.

Potential Natural Vegetation. There is bluestem prairie with northern flood plain forest along major drainages.

Fauna. Bison and pronghorn antelope were once numerous in this Section. White-tailed deer are now the most common large mammal. Smaller mammals include jack rabbits, cottontails in areas of streams and cover, and many smaller rodents. Coyotes, red foxes, and bobcats are mammalian predators. Bobwhites, horned larks, and meadowlarks are present in large numbers. Cooper's hawks, red-tailed hawks, and barred owls are year-round residents. Purple martins and swallows are summer nesters. The Section is at the northern end of winter range for gadwalls, green-winged teals, and lesser scaups. Herpetofauna include snapping turtles, bullfrogs, ringneck snakes, and bull snakes. Catfish species are common in rivers and lakes, along with largemouth bass and black crappie.

Climate. Precipitation averages 24 to 35 in (620 to 900 mm). Temperature averages 50 to 61 oF (10 to 16 oC). The growing season lasts 160 to 190 days.

Surface Water Characteristics. There is a low density of small to medium size intermittent and perennial streams and associated rivers, mostly with low to moderate rates of flow and moderate velocity. Dendritic drainage pattern has developed on maturely dissected surfaces, largely without bedrock structural control. Few natural lakes occur.

Disturbance Regimes. Fire and drought have probably been the principal historical sources of disturbance.

Land Use. Land use has caused conversion from native vegetation to agricultural crops on about 75 percent of the area.

Cultural Ecology. Reserved.

Compiled by Rocky Mountain Region.

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Section 251G--Central Loess Plains

Geomorphology. Dissected loess plains comprise this Section. It has gently rolling smooth, and irregular plains mantled by loess. Drainage pattern cuts into upper loess mantle and exposes older Loveland loess. Stream valleys are narrow, not deeply incised. Local relief ranges from tens to hundreds of ft. This Section is in the Central Lowlands and Great Plains geomorphic provinces. Elevation ranages from 600 to 1,970 ft (183 to 600 m).

Lithology and Stratigraphy. The Section is predominantly Quaternary glacial till, lacustrine, and fluvial deposits, with local windblown dune sand and loess. In the extreme southwest part of the Section is an area of Paleozoic carbonates and shales.

Soil Taxa. Types include dry Mollisols and Entisols, Mesic Ustolls, and Udolls. Entisols, Mollisols, and Alfisols with udic and aquic moisture regimes occur along major drainages.

Potential Natural Vegetation. There is bluestem prairie with northern flood plain forest along major drainages.

Fauna. Bison were once present in great numbers, and pronghorn antelope extended their eastern range through this Section. White-tailed deer are now the most common large mammal. Smaller mammals include jack rabbits, cottontails, opossum, and many small rodents. Swift foxes, kit foxes, bobcats, and coyotes are predators. Bobwhites, horned larks, and meadowlarks are plentiful. Cooper's hawks, barred owls, and long-eared owls are year-round residents. Herpetofauna include snapping turtles, box turtles, bullfrogs, ringneck snakes, and bull snakes. Catfish species, largemouth bass, and black crappie are typical fish of the area.

Climate. Precipitation averages 25 to 35 in (630 to 900 mm). Temperature averages 46 to 57 oF (8 to 14 oC). The growing season lasts 150 to 190 days.

Surface Water Characteristics. The Platte, Republican, Big Blue, and Little Blue Rivers flow through this Section. Hard groundwater is abundant in sand and gravel, but is scarce in areas where shale and clay are near the surface. Two sizable reservoirs in the area are Turtle Creek and Milford. There is a relatively low frequency of shallowly intrenched, slow flowing, meandering streams. Also characteristic of this area are small marshes and prairie potholes, many of which have been drained.

Disturbance Regimes. Drought and fire are probably the principal sources of disturbance.

Land Use. This area is highly productive farmland; about 60 percent is in crops and about 25 percent is used for grazing. Irrigation by wells and canals is common in the north. Most of the small marshes and prairie potholes were drained for agricultural uses.

Cultural Ecology. Reserved.

Compiled by Rocky Mountain Region.

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