Chapter 41
Ecological Subregions of the United States

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Great Plains-Palouse Dry Steppe

Ten Sections have been delineated in this Province:

These Sections are located in the north-central conterminous States, including parts of Oklahoma, Kansas, Colorado, Nebraska, Wyoming, South and North Dakota, and Montana. The area of these Sections is about 290,700 mi2 (752,900 km2).

Section 331A--Palouse Prairie

Geomorphology. This Section comprises moderately to strongly dissected loess-covered basalt plains, hills with large steptoes, undulating plateaus, and some river breaklands. Mountains occur in the southeast part of the Section. This Section is within the Columbia Plateau physiographic province. Elevation ranges from 1,200 to 6,000 ft (366 to 1,830 m).

Lithology and Stratigraphy. There is Tertiary basalt with some Paleozoic granitic and metasedimentary outcrops in breaklands. Granitoid rocks of the Blue Mountain uplift are evident, as well as sedimentary rocks which occur at the boundaries of the flood basalt deposits. Soil Taxa. Soils include mesic Xerolls with some Xeralfs, Albolls, and Aquolls. These soils are generally deep, loamy to silty, and have formed in loess, alluvium, or glacial outwash. Soils in mountainous areas are shallower and contain rock fragments.

Potential Natural Vegetation. Grasslands and meadow-steppe vegetation dominated by grasses are the prototypical vegetation of the Palouse. Woodlands and forests occur in the eastern portion of the Section on hills and low mountains. The relatively arid western portion of the Section is dominated by grassland, where bluebunch wheatgrass and Idaho fescue are the most prominent. Meadow-steppe vegetation characterized by Idaho fescue and common snowberry dominates areas with more precipitation, but still too dry to support forest vegetation on deep loamy soils. Most of this meadow-steppe as well as the grassland to the west, has been converted to crop lands. Ponderosa pine woodlands and forests form the lower timberline in the eastern portion of the Section on hills and low mountains. The transition zone between forest and meados-steppe consists of a complex interfingering between these two vegetation types. Douglas-fir series forests dominate at higher elevations in the mountains. Isolated fragments of the Western Red Cedar series and Grand Fir series occur on sheltered north slopes in the mountains.

Fauna. Birds are typical of grasslands with intermittent riparian systems and pine hills. Grassland species include American kestrel, ring-necked pheasant, upland sandpiper, western kingbird, horned lark, black-billed magpie, western meadowlark, and savanna sparrow. Riparian system species include Lewis' woodpecker, gray catbird, western bluebird, orange-crowned warbler, northern oriole, black-headed grosbeak, and lazuli bunting. Birds which reach or nearly reach the extent of their range include mountain quail, barn owl, white-headed woodpecker, eastern kingbird, and American redstart. The bald eagle, an endangered species, also occurs around larger water bodies. Typical herbivores and carnivores include white-tail deer, mule deer, and bobcat. Smaller common herbivores include the blacktail jackrabbit and Washingtion ground squirrel. Rare species include the whitetail jackrabbit, and possibly the pygmy rabbit. Herpetofauna typical of this Section are the bullfrog, painted turtle, western fence lizard, and the northern Pacific rattlesnake.

Climate. Precipitation ranges from 10 to 30 in (250 to 760 mm), evenly distributed throughout fall, winter, and spring. Winter precipitation is mostly snow; summers are relatively dry. Climate is warm temperate with a maritime influence. Temperature averages 45 to 54 oF (7 to 12 oC). The growing season lasts 100 to 170 days.

Surface Water Characteristics. There are scattered coulees and deeply-incised major drainages. Loess plains have low to medium density dendritic drainage patterns. Rapid changes in runoff volumes are possible on basalt due to gain or loss of water to gravel interbeds. The Snake River flows through this Section.

Disturbance Regimes. Wind is the principal source of natural disturbance.

Land Use. Dry farming and livestock grazing occurs on about 90 percent of the area. Cultural Ecology. Reserved.

Compiled by Northern Region.

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Section 331B--Southern High Plains

Geomorphology. This Section is in the Great Plains geomorphic province. The predominant landform is a broad, extensive flat plain formed by fluvial sedimentation of continental erosional products from adjacent mountain ranges, followed by sheet erosion and transport. These processes resulted in a region of moderate dissection. Landforms consist mostly of smooth plains with smaller areas of tablelands. Elevation ranges from 2,600 to 4,000 ft (800 to 1,200 m). Local relief ranges mainly from 100 to 300 ft (90 m). A small area of tablelands is present where relief ranges from 300 to 500 ft (90 to 150 m).

Lithology and Stratigraphy. Rocks were formed during the Paleozoic (20 percent), Mesozoic (20 percent), and Cenozoic (60 percent) Eras. Paleozoic strata consist of Permian marine deposits (shale and limestone). Mesozoic strata consists of Upper Cretaceous marine deposits (limestone and sandstone). Cenozoic strata consists of Quaternary continental deposits (poorly consolidated silt, sand, and gravel in varying proportions) and other localized marine deposits.

Soil Taxa. Soils are Ustolls and Ustalfs. Paleustolls, Argiustolls, Paleustalfs, and Haplustalfs are on uplands. Calciustolls, Haplustolls, and Paleustolls are on ridges and steeper slopes. Haplustolls occur on young valley floors. Pellusterts are in clayey playa lake basins. Calciorthids, Paleorthids, and Torriorthents are steep slopes in breaks. These soils have a mesic or thermic temperature regime, an ustic moisture regime, and mixed or carbonatic mineralogy. Soils are deep, fine to coarse textured, well drained, and have limited soil moisture for use by vegetation during parts of the growing season.

Potential Natural Vegetation. K\"uchler classified vegetation as sandsage-bluestem prairie and bluestem-grama prairie. The predominant vegetation form is short to mid-height grasslands. Species composition includes bluegrama, buffalograss, hairy grama, and little bluestem.

Fauna. Large to medium size herbivores and carnivores typical of this Section include pronghorn, coyote, and ringtail. Smaller herbivores include desert shrew, black-tailed prairie dog, Plains pocket mouse, silky pocket mouse, and hispid pocket mouse. Bison and black-footed ferret are historically associated with this Section. Birds of grasslands include lesser prairie chicken, Swainson's hawk, and burrowing owl. Typical reptiles and amphibians include Great Plains toad, red spotted toad, lesser earless lizard, round-tailed horned lizard, Great Plains skink, and Plains black-headed snake.

Climate. Annual precipitation averages 16 to 20 in (400 to 520 mm). Between 16 to 35 in (400 to 900 mm) of snow occurs. Temperature ranges from 50 to 57 oF (10 to 14 oC). The growing season lasts 140 to 185 days.

Surface Water Characteristics. There is a low density of small intermittent streams with low volume of water flowing at low velocity. A dendritic drainage pattern has developed on a weakly dissected plateau, largely without bedrock structural control. Major rivers include the Cimarron and North Canadian.

Disturbance Regimes. Reserved.

Land Use. Natural vegetation has been converted to agricultural crops and range for cattle grazing on about 90 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southern Region and Southeastern Forest Experiment Station.

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Section 331C--Central High Tablelands

Geomorphology. This Section includes broad intervalley remnants of smooth fluviatile plains. Smooth loess-mantled tablelands with gently rolling slopes and major valleys are bordered by steep slopes. Broad, level flood plains and terraces occur on major rivers and streams. This Section is in Fenneman and Johnson's Great Plains geomorphic physical division. Elevation ranges from 2,625 to 3,950 ft (800 to 1,200 m).

Lithology and Stratigraphy. The Colorado part of the Section is Tertiary sandstones, siltstones, and conglomerates and Quaternary windblown dune sands and loess, with Cretaceous marine shales and Quaternary alluvium in the major drainages. The Nebraska and Kansas part of the Section is mostly Quaternary windblown dune sands and loess, some Tertiary sandstones, shales, and conglomerates, and Cretaceous shales and limestones with Quaternary alluvium in stream valleys.

Soil Taxa. This area has mesic temperature and ustic moisture regimes. Soil include Mollisols, Entisols, and Alfisols.

Potential Natural Vegetation. K\"uchler mapped vegetation as grama-buffalo grass prairie, bluestem-grama prairie, sandsage-bluestem prairie, and wheatgrass-bluestem-needlegrass prairie. The predominant vegetation is short grass prairie.

Fauna. Bison, wolves, and black-footed ferrets are historically associated with this Section. Present large mammals include white-tailed deer, mule deer, and a small population of pronghorn antelope. Typical small mammals include the bobcat, red fox, jackrabbit, cottontail, and prairie dog. Year-round typical avifauna include the introduced ring-necked pheasant, horned lark, bobwhite, Cooper's hawk, and prairie falcon. Summer nesters include Swainson's hawk, blue-winged teal, and ruddy duck. The goshawk may be a rare winter resident. The goldeneyes and common merganser are other winter residents. Herpetofauna include snapping turtle, Great Plains toad, wester hognose snake, and the western garter snake. Catfish species are typical in area waters.

Climate. Precipitation averages 16 to 21 in (400 to 530 mm). Temperature averages 50 to 57 oF (10 to 14 oC). The growing season lasts 140 to 185 days.

Surface Water Characteristics. There are many major rivers in this area, including North and South Platte, Republican, Arkansas, Smoky Hill, Saline, Arikaree, and North and South Fork of the Solomon. In most of the area, good quality ground water is available, but it is scarce where shale is near the surface.

Disturbance Regimes. Fire, insects, and disease are predominant disturbance regimes.

Land Use. Nearly all of this area is in farms and ranches; about 60 percent is cropland. This is a major dry farming area. Irrigation occurs along major rivers.

Cultural Ecology. Reserved

Compiled by Rocky Mountain Region.

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Section 331D--Northwestern Glaciated Plains

Geomorphology. This Section includes level to gently rolling continental glacial till plains and rolling hills on the Missouri Plateau. Steep slopes border some of the larger rivers. Elevation ranges from 2,500 to 5,000 ft (763 to 1,525 m). This Section is within the Great Plains physiographic province.

Lithology and Stratigraphy. Glacial till is underlain by soft Cretaceous marine shale.

Soil Taxa. Soils include frigid Borolls, Ustochrepts, Natriborolls, and Orthents with some Fluvents along the rivers. These soils are generally deep and range in texture from loamy to clayey.

Potential Natural Vegetation. K\"uchler mapped vegetation as grama-needlegrass-wheatgrass. Common species include blue grama, bluebunch wheatgrass, green needlegrass, needleandthread, western wheatgrass, and basin wildrye.

Fauna. Birds are typically grassland associated species or those associated with prairie potholes. These include the ferruginous hawk, Swainson's hawk, golden eagle, sharp-tailed grouse and sage grouse, mountain plover, clay-colored sparrow, and dabbling ducks. Riparian areas also provide for some woodland species at the edge of their ranges such as eastern screech-owl, red-headed woodpecker, and ovenbird. Other species which nearly reach the edge of their ranges in this Section are Sprague's pipit and Baird's sparrow. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, bobcat, and cougar. Smaller common herbivores include the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common species associated with this Section includes black-tailed jackrabbit, swift fox, dwarf shrew, and Canadian toad. The black-footed ferret and bison are species which historically occurred here. Herpetofauna typical of this Section are the snapping turtle, spiney softshell turtle, smooth green snake, and the prairie rattlesnake.

Climate. Precipitation averages 10 to 15 in (250 to 380 mm), with maximum occurring in spring and early summer. Winters are extremely, cold with desiccating winds and snow. Climate is cold continental, with dry winters and warm summers. Temperature averages 37 to 45 oF (3 to 7 oC). The growing season lasts 100 to 130 days.

Surface Water Characteristics. There are high density dendritic drainage patterns on areas of exposed marine shales. Low to medium density drainage patterns occur on the better drained glacial till. The higher order streams show subtle structural and glacial influence. Major rivers include the Milk and the Poplar.

Disturbance Regimes. Fire and drought are the principal sources of natural disturbance.

Land Use. Most of the area is in crop land or is grazed by livestock.

Cultural Ecology. Reserved.

Compiled by Northern Region.

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Section 331E--Northern Glaciated Plains

Geomorphology. This area includes gently undulating to rolling continental glacial till plains with areas of kettle holes, kames, and moraines. Slopes adjacent to major stream valleys are steep. Elevation ranges from 2,000 to 6,000 ft (610 to 1,830 m). This Section is within the Great Plains physiographic province.

Lithology and Stratigraphy. Glacial till is underlain by soft Cretaceous and Lower Tertiary non-marine sedimentary rocks.

Soil Taxa. Soils include predominantly frigid Borolls. These soils are generally deep and have loamy textures.

Potential Natural Vegetation. K\"uchler mapped vegetation as wheatgrass-needlegrass. The natural prairie vegetation is characterized by western wheatgrass, needleandthread, green needlegrass, and blue grama. Little bluestem occurs on sloping and thin soils. Prairie cordgrass, northern reedgrass, and slim sedge occur on wet soils. Western snowberry and prairie rose are common shrubs.

Fauna. Birds are very similar to those that occur in Section 332A, but include some species associated with the Missouri River (Missouri Coteau region). These species are typical of riparian habitat, or typical of both prairie potholes and badlands. Several species follow the Missouri River upstream to near the western extent of their ranges; these include piping plover, least tern, chimney swift, eastern phoebe, purple martin, eastern bluebird, black-and-white warbler, ovenbird, indigo bunting, rose-breasted grosbeak, orchard oriole, and field and swamp sparrows. Western species reaching the edge of their range include lazuli bunting and black-headed grosbeak. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, and bobcat. Smaller common herbivores include the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common species associated with this Section includes black-tailed jackrabbit, swift fox, dwarf shrew, and hispid pocket mouse. The black-footed ferret and bison are species which are historically associated with this Section. Herpetofauna typical of this Section are the snapping turtle, spiney softshell turtle, smooth green snake, and the prairie rattlesnake.

Climate. Precipitation ranges from 10 to 20 in (250 to 510 mm) with more than half falling during the growing season. Winters are extremely cold with desiccating winds; precipitation is snow. Climate is cold continental, with warm, dry summers. Temperature averages 37 to 45 oF (3 to 7 oC). The growing season lasts 110 to 135 days.
Surface Water Characteristics. Low to medium density dendritic drainage patterns change to complex, high density dendritic patterns where the sedimentary rocks are exposed due to erosion of badlands.

Disturbance Regimes. Fire and drought are the principal natural sources of disturbance.

Land Use. Dryland farming and livestock grazing occur on most of the area.

Cultural Ecology. Reserved.

Compiled by Northern Region.

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Section 331F--Northwestern Great Plains

Geomorphology. This area includes gently sloping to rolling, moderately dissected shale plains. There are some steep, flat-topped buttes, particularly in eastern Wyoming. Badlands with eroded escarpments are in North Dakota and western South Dakota. Elevation ranges from 1,500 to 3,900 ft (458 to 1,200 m). This Section occurs on the Missouri Plateau and High Plains within the Great Plains physiographic province.

Lithology and Stratigraphy. This Section has soft Cretaceous and Lower Tertiary non-marine sedimentary rocks.

Soil Taxa. Soils include mesic and frigid Borolls and Ustolls, particularly in the northern, southern, and eastern parts of the Section. These soils are generally moderately deep to deep and have loamy to clayey textures. Argids, Orthents, and Orthids also occur, mostly in the central and western parts of the Section and on the badlands. These soils range from shallow to deep and generally have clayey textures.

Potential Natural Vegetation. K\"uchler mapped vegetation as wheatgrass-needlegrass. Most of the Section has natural prairie vegetation, which includes western wheatgrass, green needlegrass, blue grama, needleandthread, and buffalograss. Bluebunch wheatgrass, little bluestem, and sideoats grama occur on shallow soils. Common shrubs in draws and along streams include buffaloberry, chokecherry, snowberry, and sagebrush. Ponderosa pine, juniper, and some aspen occur in North Dakota and on the Pine Ridge in South Dakota.

Fauna. Birds are dry grassland and badland species, and riparian associates. Typical species are ferruginous hawk, golden eagle, sharp-tailed grouse and sage grouse, gray partridge, mourning dove, black-billed magpie, horned lark, western meadowlark, lark bunting, grasshopper sparrow, and chestnut-collared longspur. Riparian or wetland associated species include dabbling duck, eastern kingbird, blue jay, brown thrasher, and yellow warbler. Species near the edge of their range include chimney swift; eastern, western and mountain bluebirds; dickcissel; field sparrow; and orchard oriole. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, and bobcat. Smaller common herbivores include the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common species associated with this Section includes bighorn sheep and the black-tailed jackrabbit. Rare species includes the black-footed ferret. Bison are historically associated with this Section. Herpetofauna typical of this Section are the snapping turtle, spiney softshell turtle, smooth green snake, and prairie rattlesnake.

Climate. Precipitation ranges from 10 to 20 in (250 to 510 mm), with more than half falling during the growing season. Winters are extremely cold with desiccating winds. Precipitation is snow. Climate is cold continental. Temperature averages 37 to 48 oF (3 to 9 oC). The growing season lasts 110 to 160 days.

Surface Water Characteristics. There are long, structurally controlled second and third order streams with low gradient, which are fed by high density, dendritic first order tributaries. Alternating hard and soft layers at low angles produce a complex pattern of resistant layers, temporary base levels, and headward and sideward erosion by undercutting. Ground water is scarce over most of the area but does occur locally in sand and gravel deposits. Major rivers include the Missouri, Cheyenne, Little Missouri, and Niobrara.

Disturbance Regimes. Fire and drought are the principal natural sources of disturbance.

Land Use. Dryland farming and livestock grazing occur on about 85 percent of the area. Some commercial timber harvests also occur.

Cultural Ecology. Reserved.

Compiled by Northern Region.

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Section 331G--Powder River Basin

Geomorphology. This area includes gently rolling to steep dissected plains on the Missouri Plateau. Wide belts of steeply sloping badlands border a few of the larger river valleys. In places, flat-topped, steep-sided buttes rise sharply above the surrounding plains. Elevation ranges from 3,000 to 6,000 ft (915 to 1,830 m). This Section is within the Great Plains physiographic province.

Lithology and Stratigraphy. There are Cretaceous and Lower Tertiary non-marine sedimentary rocks. Glacial lake beds also occur.

Soil Taxa. Soils include Orthents, Orthids, Argids, Borolls, and Fluvents. Temperature regimes are generally frigid in the north and mesic in the south. These soils are mostly medium to fine texured and range from shallow to deep.

Potential Natural Vegetation. K\"uchler mapped vegetation as grama-needlegrass-wheatgrass. About 20 percent of the area supports eastern ponderosa forest. Dominant grassland species include western wheatgrass, blue grama, green needlegrass, bluebunch wheatgrass, and needleandthread. Little bluestem replaces bluebunch wheatgrass in the eastern part of the Section. Basin wild rye and sagebrush occur along streams and on bottomlands.

Fauna. Typical birds are sagebrush obligates or specialists, such as sage grouse, sage thrasher, and sage and Brewer's sparrows; sage thrasher and sage sparrow near the edge of their ranges in this Section. Other specialists are ferruginous and Swainson's hawks, golden eagle, Say's phoebe, and McCown's longspur. Typical riparian species include Lewis' woodpecker, yellow warbler, and lazuli buntings. Several bird species that reach or nearly reach the extent of their ranges in this Section are eastern screech-owl, red-headed woodpecker, Cassin's kingbird, pinyon jay, green-tailed towhee, and clay-colored sparrow. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, bobcat, and cougar. Smaller common herbivores include the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common is the black-tailed jackrabbit. The black-footed ferret is a rare species within this Section. Bison are historically associated with this Section. Herpetofauna typical of this Section are the Great Plains toad, snapping turtle, spiney softshell turtle, smooth green snake and prairie rattlesnake.

Climate. Precipitation ranges from 10 to 20 in (250 to 510 mm), most of which falls as spring and summer rain. Winter precipitation is snow. Climate is cold continental with dry winters and warm summers. Temperature averages 39 to 45 oF (4 to 7 oC). The growing season lasts 120 to 140 days.

Surface Water Characteristics. Low to medium density drainages occur on more permeable surfaces. Large, shallow head basins underlain by coal or scoria are water collection areas. Much of the drainage pattern is structurally controlled. Major rivers include the Yellowstone, Tongue, and Powder.

Disturbance Regimes. Fire and drought are the principal natural sources of disturbance.

Land Use. Livestock grazing is the dominant land use; a small amount of dryland farming also occurs.

Cultural Ecology. Reserved.

Compiled by Northern Region.

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Section 331H--Central High Plains

Geomorphology. This Section includes undulating to rolling plains, moderately dissected by streams. There are steep slopes, large streams, and isolated mesas, with rolling to hilly sand dunes that border some valleys. Local relief ranges up to tens of meters. Elevation ranges from 3,610 to 5,905 ft (1,100 to 1,800 m). This Section is in Fenneman and Johnson's Great Plains geomorphic physical division.

Lithology and Stratigraphy. Parts of the Section in southwestern Nebraska, southeastern Wyoming, and extreme northeastern Colorado is Tertiary ashy claystones and sandstones, with local conglomerates. Part of the extreme northeastern part of Colorado is also windblown dune sand, silt, and loess. The western part and southeast extension of the Section is Cretaceous shales, sandstones, siltstones, and local coals, with some calcareous shales and limestones in the extreme southeast. The extreme northwest part of the Section is a thin band of Pennsylvanian through Cretaceous sandstones, siltstones, shales, and some conglomerates. The extreme southwestern is Tertiary arkosic sandstones and conglomerates.

Soil Taxa. There are mesic temperature and ustic moisture regimes. Soils include Mollisols, Entisols, and Alfisols.

Potential Natural Vegetation. Predominant vegetation is short and mid grass prairie. K\"uchler classified potential vegetation as grama-buffalo grass prairie and sandsage-bluestem prairie, with northern floodplain forest along major drainages.

Fauna. Bison and wolves are historically associated with this Section. Current herbivores are white-tailed deer, mule deer, pronghorn antelope, prairie dog, jackrabbit, and cottontail. Red fox, bobcat, and coyote are the chief mammalian predators. Typical year-round bird species include horned lark, burrowing owl, prairie falcon, and kestrel. Summer nesters include Swainson's hawk, western and eared grebes, ruddy duck, and the western range of the red-headed woodpecker. Winter residents include northern shrike, golden-crowned kinglet, and goldeneye duck. Typical herpetofauna include hognose snake, prairie rattlesnake, Great Plains toad, snapping turtle, and painted turtle. Catfish species exist in rivers and lakes.

Climate. Precipitation averages 13 to 17 in (320 to 420 mm). Temperature averages 45 to 50 oF (7 to 10 oC). The growing season lasts 120 to 160 days (180 days in extreme south).

Surface Water Characteristics. The North and South Platte Rivers and their tributaries flow through here. Ground water is scarce and of poor quality where shale bedrock is near the surface. In much of the area, sand and gravel yield adequate amounts of ground water.

Disturbance Regimes. Fire, insects, and disease are predominant natural disturbances.

Land Use. Most of the area is in farms and ranches; there is some urban use on the western edge. About 60 percent of the area is rangeland grazed by cattle and sheep. About 25 percent of the area is in dry crops. An extensive amount of acreage is irrigated, water is usually obtained from rivers.

Cultural Ecology. Reserved.

Compiled by Rocky Mountain Region.

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Section 331I--Arkansas Tablelands

Geomorphology. This Section includes undulating to rolling plains composed of shale that are moderately dissected by streams. In many places the shale is mantled by loess, alluvium, and outwash. Large stream valleys and isolated mesas with steep slopes and rolling to hilly dunes border some of the valleys. Local relief ranges from 10 to 300 ft (3 to 90 m). Elevation ranges from 3,610 to 6,235 ft (1,100 to 1,900 m). This Section is in Fenneman and Johnson's Great Plains geomorphic physical division.

Lithology and Stratigraphy. The north-central one-third of the Section is predominantly Quaternary eolian deposits, including windblown dune sand, silt, and loess, and local gravels and alluvium. The extreme northwest is Tertiary arkosic sandstones and conglomerates, with local ashy claystones and sandstones. Extreme southeast is Tertiary that is loose to well-cemented sand and gravel. The remainder of the Section (generally southern two-thirds) is Permian through Cretaceous sandstones, locally conglomeratic, and siltstones and shales, with local limestones. Western part of the southern 2/3 of the Section has more calcareous shales and limestones. A small area in the extreme south is Tertiary basalt flows and associated tuffs, breccias, and conglomerates.

Soil Taxa. There are mesic temperature and ustic moisture regimes. Soils include Mollisols, Entisols, and Alfisols.

Potential Natural Vegetation. Predominant vegetation consists of short and mid grass prairie, and some woodlands. K\"uchler classified vegetation as grama-buffalo grass prairie, sandsage-bluestem prairie, and juniper-pinyon woodland.

Fauna. Buffalo and wolves are historic residents of this Section. Large mammals include white-tailed deer, mule deer, and pronghorn antelope. Elk, black bear, and mountain lion occasionally come into the Section from the west. Horned lark, northern harrier, prairie falcon, and burrowing owl are year-round residents; the northern range of the roadrunner extends to this Section. Summer nesters include Swainson's hawk, western and eared grebes, and ruddy duck. Winter residents include marlin, northern shrike, Brewer's blackbird, and cedar waxwing. Typical herpetofauna include the prairie rattlesnake, gopher snake, snapping turtle, and Great Plains toad. Catfish species are present in rivers and lakes.

Climate. Precipitation averages 10 to 17 in (250 to 430 mm). Temperature averages 45 to 50 oF (7 to 10 oC). The growing season lasts 120 to 180 days.

Surface Water Characteristics. Ground water is associated with sand and gravel over much of the area, but is scarce where shale bedrock is near the surface. The Arkansas, Chuchara, Purgatoire, Apishipa, and St.Charles Rivers flow through here. Local wells exist.

Disturbance Regimes. Fire, drought, insects, and disease have been the principal historical source of disturbance.

Land Use. Almost all of the area is in farms and ranches, but urban areas do occur along the western edge near Denver and other cities. About 68 percent of the area is used for grazing purposes. About 8 percent of the area is irrigated, and about 15 percent of the area is in dry crops.

Cultural Ecology. Reserved.

Compiled by Rocky Mountain Region.

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Section 331J--Northern Rio Grande Basin

Geomorphology. This area is in the Southern Rocky Mountain Province. This Section is located in north-central New Mexico and south-central Colorado. Landforms include valley, lowland, and elevated plains and hills. Elevation ranges from 6,875 to 8,800 ft (2,100 to 2,680 m). The major landform features are The San Luis Valley and the Rio Grande River.

Lithology and Stratigraphy. There are mostly Cenozoic sedimentary rocks and a few tertiary volcanic rocks. Included also are terrestrial basin fill of late Tertiary and Quaternary age.

Soil Taxa. Soils include Inceptisols, Alfisols, Entisols, Aridisols, and Mollisols. Temperature regimes range from mesic to frigid. Moisture regimes range from ustic to aridic.

Potential Natural Vegetation. Grama, galleta and sand dropseed grasses and Great Basin big sagebrush are found in ustic soil moisture regimes and cottonwood and willow along riparian corridors. Fescue-mountain muhly prairie also occurs. K\"uchler mapped potential vegetation as saltbush-greasewood and wheatgrass-needlegrass.

Fauna. This Section was once characterized by bison and large carnivores such as the gray wolf and grizzly bear. These species have been reduced, primarily at the hand of man, yet occasionally are still reported in the area. Currently, large ungulates include Rocky Mountain elk, mule deer, bighorn sheep, antelope, and moose; cougar, black bear, and coyotes comprise the large predator component throughout the Section. Historical and present-day herpetofauna include the Wyoming and western toads; spotted and northern leopard frogs; tiger salamander; short-horned and sagebrush lizards; the gopher snake, rubber boa, racer, and several species of garter. Habitats in this Section support a rich and diverse avifauna: neotropical migratory landbirds; waterfowl, including trumpeter swans and common loons; raptors, including bald and golden eagles and peregrine falcons; and gallinaceous species. The Colorado River cutthroat trout represents the historic salmonid component. Other fish that now inhabit the waters within this Section include: the rainbow, brown, brook, golden, mackinaw, and hybrid trout, plus arctic grayling; Rocky Mountain whitefish; speckled dace; squawfish; and others. Of special note is the Kendall Warm Springs dace, found only in this Section and only in one stream.

Climate. Precipitation ranges from 6 to 20 in (150 to 500 mm) annually with less than half of the precipitation falling during the winter. Temperature averages 39 to 57oF (4 to 14oC) and winters are generally cold. The growing season lasts 100 to 140 days

Surface Water Characteristics. There is limited precipitation; irrigation water is provided by the Rio Grande River and small reservoirs supported by run off from nearby mountains. Wells can tap ground water in deep soils in valley plains. The Chama River is an important water source in the south part of this Section. The Conejos River flows through here.

Disturbance Regimes. Soil salinity is a problem in much of the area.

Land Use. Much of this Section is in farms and ranches. About 25 percent of this area is irrigated cropland. Grazing and recreation are important activities.

Land Use. The Great Sand Dunes National Monument is located in this Section. About 50 percent of the area is Federally owned and about 50 percent is in farms and ranches. About 25 percent of the area is irrigated. Some grazing on native rangeland occurs.

Cultural Ecology. Humans have inhabited and made use of the Upper Rio Grande Basin for perhaps the past 12,000 or 13,000 years. For almost all of that time, people were hunters and gathers. Virtually every one of the various ecological zones within the basin was known and used in the battle for survival. This quest mandated a non-sedentary existence and did not allow for substantial groupings of people to cluster together for more than relatively short periods of time. Sometime between 1,000 and 2,000 years ago, people began to master the techniques of being successful agriculturalists. This resulted in significant lifestyle changes. Only portions of the basin were suitable for habitation: those where the elevation was low enough and the latitude southerly enough to provide growing seasons of sufficient length. This same agricultural lifestyle allowed for people to gather into sedentary groups and led to the rise of full-blown civilization.

In the last few hundred years, Euro-Americans have come to join native Americans in the Rio Grande Basin. With them they brought new ideas of land use. Once again, all of the basin's ecological zones are utilized. shepherds graze their sheep in the high country and miners extract minerals--even above timberline. Contemporary cultural components include Anglo, Hispanic, and Puebloan (Taos). Tourism and recreation are major contributors to today's economy, along with ranching and mining.

Compiled by Southwestern Region and Rocky Mountain Region.

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