Chapter 49
Ecological Subregions of the United States



Nevada-Utah Mountains Semi-Desert - Coniferous Forest - Alpine Meadow

Three Sections have been delineated in this Province:

These Sections are located in the west-central conterminous States, including parts of Nevada, Utah, and Colorado. The area of these Sections is about 43,600 mi2 (112,900 km2).

Section M341A--Central Great Basin Mountains

Geomorphology. This area occurs within the Central Nevada Basin and Range physiographic province. The Central Great Basin Mountains section is located in central Nevada and a small area of western Utah. The dominant landforms are north-south trending mountains separated by broad, sediment-filled valleys, many of which have internal drainages. Mountains were formed by faulting and were subsequently modified by erosion. Large alluvial fans have developed at the mouths of most canyons. Some fans are coalescing, nearly burying the eroded mountains. Elevation ranges from 5,000 to 13,000 ft (1,500 to 4,000 m).

Lithology and Stratigraphy. Undifferentiated volcanic rocks from the Miocene and Oligocene epochs occur in this Section. Rhyolites and andesites also occur. Sedimentary rocks from the Miocene-Pliocene epoch, along with rocks from the Pennsylvanian period, are found, and limestone and dolomite from the Cambrian period occur. Intrusive igneous rocks form many of the mountain ranges. Playas are also evident in the internally drained valleys of this Section. Alluvial deposits occur in most of the valleys, and these include sand dunes.

Soil Taxa. Entisols and Aridisols occur in combination with mesic, frigid, and cryic soil temperature regimes, along with xeric and aridic soil moisture regimes. Large areas have saline-sodic affected soils.

Potential Natural Vegetation. K\"uchler vegetation types include Great Basin sagebrush and areas of saltbush-greasewood and juniper-pinyon woodlands. The Soil Conservation Service identifies the potential natural vegetation as saltbush-greasewood, big sagebrush, and pinyon-juniper woodland vegetation.

Fauna. During the Pliocene and the Pleistocence epochs, camels, horses, elephants, and bison were all abundant; early human inhabitants extirpated all but the bison. Bighorn sheep and pronghorn antelope were once common. Today bighorn sheep are being re-introduced to native ranges; pronghorn antelope are greatly reduced in range and number. Presently the common ungulates are mule deer and introduced elk. Coyote and mountain lion are the typical large predators. Characteristic herpetofauna include western whiptail, rubber boa, common garter snake, leopard lizard, side-blotched lizard, and western toad. Fossil evidence indicates that historic bird populations are similar to what can be found presently, none of which are endemic. Sage grouse, sage thrasher, and sage sparrow are birds which characterize and are almost exclusively found in the sagebrush communities. Cassin's kingbird, gray flycatcher, scrub jay, pinyon jay, plain titmouse, bush-tit, blue-gray gnatcatcher, cedar waxwing, gray vireo, black-throated gray warbler, and Brewer's sparrow typify the pinyon-juniper woodlands.

Climate. Precipitation ranges from 5 to 25 in (125 to 625 mm) annually; the driest period is from midsummer to midautumn. Summers are dry and hot with low humidity. Winters are cold and dry. Temperature averages 38 to 50 oF (4 to 10 oC). The growing season ranges from 60 to 120 days.

Surface Water Characteristics. Water is scarce. Streams are small and intermittent. Reese River and Duck Creek are some of the major drainages in this Section. Small streams drain the mountain ranges and all areas have internal drainage. Ground water is also scarce.

Disturbance Regimes. Erosion by wind and water is occurring. Fires also occur.

Land Use. Livestock grazing is the primary use, with small areas used as hay fields and pasture land. Some mining has also occurred.

Cultural Ecology. Reserved.

Compiled by Intermountain Region.


Section M341B--Tavaputs Plateau

Geomorphology. This area occurs within the Colorado Plateau physiographic province. The Tavaputs Plateau Section is located in eastern Utah and western Colorado. One of Utah's most rugged areas is between the relatively level interior of the Uinta Basin and the valleys cut in the Mancos Shale in Carbon, Emery, and Grand Counties. The structure is relatively simple. Strata of Cretaceous and Tertiary periods rise gradually southward and upward from the center of the Uinta Basin to reach elevations between 8,000 and 10,000 ft where they are abruptly cut off in great erosional cliffs that descend in giant steps to the valleys of the south; there elevations are between 4,000 and 5,500 ft. The great system of linear cliffs is evident. The lower one, most visible and best known, is the Book Cliffs. Above, and separated by a bench or valley as much as 10 miles wide, are the Roan Cliffs. For that part of the Uinta rim in Carbon County, there is a third, relatively short system, the Badland Cliffs. The cliffs are retreating from former positions far to the south. The tendency to retreat along a regular front has exercised a much greater influence than the Green River, which is confined to a relatively narrow gorge through the formations without interrupting the dominantly east-west sweep of the cliff system. Desolation Canyon traverses the Tertiary Section and Gray Canyon cuts across the Cretaceous formations. In passing through these two canyons the river drops about 600 ft (180 m). Elevation ranges from 7,300 to 10,000 ft (2,100 to 3,000 m). Local relief ranges from 5 percent on the broad plateau uplands, to steep vertical canyon sidewalls comprised predominantly of bedrock.

Lithology and Stratigraphy. Cretaceous period with Paleocene and Eocene period sedimentary rocks occur, which are dominantly shales, sandstones, and siltstones. The Book Cliffs are carved mainly from marine Cretaceous sandstone, the Roan Cliffs of Paleocene and Eocene epoch river and flood plain deposits, and the Badland Cliffs are from Eocene epoch lakebeds.

Soil Taxa. Entisols and Aridisols occur in combination with mesic and frigid soil temperature regimes, along with aridic soil moisture regimes occur at the lowest elevations. Between 8,000 and 10,000 ft (2,400 to 3,000 m) elevation, Mollisols dominate with frigid and cryic temperature regimes. Inceptisols are common with Douglas-fir. Most soils have concentrations of calcium.

Potential Natural Vegetation. K\"uchler vegetation types include juniper-pinyon and big sagebrush. The eastern part of this Section (Book Cliffs-Roan Plateau-East and West Tavaputs Plateau) as delineated by Stokes includes juniper-pinyon, black sagebrush, big sagebrush, mountain brush, Salina wildrye grasslands, ponderosa pine, aspen, Douglas-fir, and spruce-fir.

Fauna. Historically, desert bighorn sheep were found in the area, but were extirpated with the advent of settlers and widespread livestock grazing. Though moose probably are not indigenous, their range is now expanding into suitable habitat. Mountain bighorn sheep have been introduced in localized areas. Ring-necked pheasants, also introduced, are becoming more abundant. Fauna representative of desert shrub communities include rock wren, lark sparrow, sage sparrow, loggerhead shrike, horned lark, green-tailed towhee, Brewer's sparrow, red-tailed hawks, golden eagle, northern harrier, and kestrel. Pinyon-juniper and mountain brush communities support a variety of species, including mountain bluebird, blue-gray gnatcatcher, red breasted nuthatch, flycatcher, great horned owl and red-tailed hawk; obligate species include the pinyon jay and pinyon mouse. Fauna representative of high elevation sagebrush communities include sage grouse, mule deer, antelope, cougar, black bear, California myotis, and faded pygmy rattlesnake. Species representative of aspen and coniferous forest include brown creeper, western wood peewee, warbling vireo, MacGillivray's warbler, Townsend's solitaire, three-toed woodpecker, red-naped sapsucker, hairy and downy woodpeckers, red-tailed hawk, goshawk, Cooper's hawk, and sharp-shinned hawk; red squirrel, northern flying squirrel, deer, elk, cougar, bear, coyote, and hoary bat; and milk snakes. Species representative of riparian areas include yellow warbler, tree swallow, western kingbird, house wren, rufous-sided towhee, song sparrow, loggerhead shrike, hairy woodpecker, red-tailed hawk, and golden eagle; deer, elk, moose, cougar, bear, beaver and silver-haired bat; and Utah tiger salamander. Colorado River cutthroat trout are present as unique stream fauna. The Green River has been proposed as critical habitat for four endangered, endemic fishes. Colorado squawfish, razorback sucker, humpback chub, and bonytail chub. Two candidate species, flannelmouth sucker and roundtail chub, also occur.

Climate. Precipitation ranges from 8 to 35 in annually (200 to 890 mm). Much precipitation falls at higher elevations during winter months in the form of snow. Summers have afternoon thunderstorms that often result in debris flows from the side canyons. Lower elevations are somewhat dry and hot in summer and cold and moist in winter. Higher elevations are warm and wet during summer, and cold and wet during winter. Fall is generally dry and cool throughout the Section. Temperature averages 34 to 45 oF (1 to 7 oC). Mean January temperature at high elevation (e.g., Strawberry) is a maximum 28 oF and a minimum 4 oF. The mean for July is a maximum 80 oF and a minimum 45 oF. At lower elevations (e.g., Antelope), mean January temperature is a maximum 28 oF and a minimum 8 oF. The mean for July is a maximum 88 oF and minimum 58 oF. High elevation areas have approximately 40 frost free days, while lower elevations have about 120 frost free days.

Surface Water Characteristics. Water is scarce over most of the area and is generally confined to steep canyons such as the Green and White Rivers. Smaller drainages such as Timber, Sowards, and Indian Canyon deliver water to the Green after flowing into the Strawberry River in the Uinta Basin. Lakes and reservoirs are few, and many water developments have been put on public lands to distribute to livestock and to provide water for wildlife.

Disturbance Regimes. Occurrence of fire is common, with large grass and shrub areas burning rapidly. At higher elevations, small fires are common, generally caused by lightening. They are usually confined to aspect and vegetation type. These fires are generally not extensive.

Land Use. Grazing, mining, recreation, and wildlife habitat are the major land uses. Hay and pasture land also occur to a very limited extent along drainage ways.

Cultural Ecology. Reserved.

Compiled by Intermountain Region.


Section M341C--Utah High Plateaus and Mountains

Geomorphology. This area occurs within the Colorado Plateau physiographic province. It includes portions of south-central Utah. This Section is located in the northwest corner of the Colorado Plateau physiographic province. These plateaus are primarily fault-controlled, have relatively high elevations, are aligned in a north-south direction, and are underlain with rocks of Mesozoic and Cenozoic eras. The east flank of the high plateaus is bordered by the Canyonlands. The western boundary is faulted, separating it from the Basin and Range physiographic province. They are a series of high plateaus that are gently rolling on top, but rise steeply from the valley bottoms. They are separated by north-south trending valleys. Landslides have influenced many areas in this Section and several plateaus were sites of local icecaps during at least the Wisconsin age. The tops of the plateaus have been capped with volcanic flows and glacial deposits. Colorful badland topography exists near Bryce Canyon and Cedar Breaks. This Section can be divided into three north-south groups that are separated from each other by two major structural trenches. The main plateaus of the western strip, from south to north, are the Markagunt, Tushar, Pavant, and Gunnison; the plateaus of the middle strip are the Pausaugunt and Sevier; those of the eastern strip are the Aquarius, Awapa, Fish Lake, and Wasatch. The depression which divides the western and middle plateau groups is the Sevier-Sanpete Valley. This depression is largely controlled by the Sevier Fault at its east side. The middle and eastern plateau strips are separated by Grass Valley, another fault-controlled depression, and by the Paunsaugunt Fault. The western boundary of the Utah High Plateaus and Mountains Section also follows the northern part of Hurricane Fault.

The general outline of this Section is determined by a series of northeast-southwest-trending faults. The boundary rises from the levels of the plateaus immediately north of the Grand Canyon to the highest of the High Plateaus and includes a series of cliffs and associated rock terraces which have been named according to the predominant colors of the geological formations responsible for them. This ascent takes place over a distance of 40 to 50 miles. The cliffs have a general east-west trend, in contrast to the faults of the area. Five cliffs have regional extent; they are, in order from south to north the Chocolate, Vermillion, White, Gray, and Pink Cliffs. Each cliff is developed on a resistant geological formation ranging in age from the Triassic period to Eocene epoch. The cliffs are cuesta scarps developed on northward-dipping resistant formations. Elevation ranges from 5,000 to 13,000 ft (1,500 to 4,100 m).

Lithology and Stratigraphy. The northern portion is Miocene, Oligocene, and other undivided Tertiary volcanic rocks. The southern portion of the Section is Jurassic, Cretaceous, and Paleocene-Eocene aged sedimentary rocks, mostly sandstones and shales.

Soil Taxa. Mollisols, Entisols, Inceptisols, and Alfisols are in combination with mesic, frigid, and cryic soil temperature regimes, along with ustic, xeric, and udic soil moisture regimes.

Potential Natural Vegetation. K\"uchler vegetation types include western spruce-fir forest, Arizona pine forest, and spruce-fir--Douglas-fir forest. The Soil Conservation Service identifies potential natural vegetation as conifer, aspen, grasses, mountain shrub, and sagebrush-grass. Areas of big sagebrush also occur.

Fauna: This section was once dominated by Rocky Mountain bighorn sheep, and large numbers of antelope and Utah prairie dogs; there were fewer bison, elk, mule deer, and wild turkeys, and desert bighorns. Rocky Mountain sheep and bison have been extirpated. Elk and wild turkey were extirpated historically, but both have been re-introduced; currently, elk are found throughout their historic range. Large predators included timber wolves, grizzly bears, black bears, cougars, bobcats, gray foxes, and coyotes. Timber wolves and grizzly bears have been extirpated. Northern goshawks, flammulated owls, wolverines, flying squirrels, red squirrels, snowshoe hares, blue grouse, Steller's, jays, and three-toed woodpeckers were found throughout spruce-fir and mixed conifer forests. Wolverines, never plentiful, are no longer found in this area, and three-toed woodpecker populations are reduced in range and number. Boreal toads, Utah tiger salamanders, and Utah mountain kingsnakes typify herpetofauna in and around high elevation ponds, lakes, wetlands, and riparian areas, although boreal toads are greatly reduced in number and range. Golden eagles, mountain bluebirds, loggerhead shrikes, Brewer's sparrows, and burrowing owls typify bird species found in plateau and valley grasslands. Ring-tailed cats and peregrine falcons were found in canyon areas; presently, peregrines are sparsely distributed throughout the Section. Riparian corridors are used by many neotropical bird species such as western wood peewee, lazuli bunting, and warbling vireo. Leatherside chub, Utah chub, and native Bonneville and Colorado cutthroat trout characterize unique stream fauna.

Climate. Precipitation ranges from 14 to 35 in (375 to 900 mm) annually, with precipitation being distributed throughout the year. Much of the precipitation falls as snow. Summer precipitation patterns provide limited moisture during the growing season. Temperature averages 32 to 47 oF (0 to 8 oC). The growing season ranges from 20 to 120 days.

Surface Water Characteristics. Streams, lakes, and ground water supply adequate water for grazing and forest growth. Perennial streams are frequent and drain into the Sevier, Virgin, or Colorado River. Some major lakes are Piute Reservoir, Panguitch Lake, Scofield Reservoir, Joes Valley Reservoir, Fish Lake, and Otter Creek Reservoir.

Disturbance Regimes. The primary disturbance forces are infrequent mass movements and erosion from water. Historically, fire was a major disturbance that modified the vegetation. Fire suppression practices during the past century has altered this process.

Land Use. Grazing for sheep and cattle is the major land use. Timber production also occurs on the high plateaus. National parks and monuments bring abundant recreational use into the area. Coal mining is an important use on the Wasatch Plateau.

Cultural Ecology. Reserved.

Compiled by Intermountain Region.