Chapter 47
Ecological Subregions of the United States

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Intermountain Semi-Desert and Desert

Seven 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 107,100 mi2 (277,400 km2).

Section 341A--Bonneville Basin

Geomorphology. This Section occurs within the Basin and Range physiographic province. 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. Playas are found in some closed basins, and salt flats are common. Elevation ranges from 4,000 to 8,000 ft (1,200 to 2,400 m).

Lithology and Stratigraphy. Miocene, Oligocene, and other undifferentiated Tertiary volcanic rocks dominate this Section. Rhyolites and basalts are also found. Sedimentary rocks from the Miocene-Pliocene epoch, sediments from the Pennsylvanian period, and limestone and dolomite from the Cambrian period also occur. Mud and salt flats are in the valleys near Great Salt Lake, along with Lake Bonneville deposits. Areas of Eolian deposits also occur. The southern portion of this Section has large areas of alluvium and colluvium.

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 are saltbush-greasewood and juniper-pinyon woodlands. Areas of sagebrush and wheatgrass-grama-buffalograss also were mapped. The Soil Conservation Service identifies the potential natural vegetation as desert shrub, shrub-grass, and woodland vegetation.

Fauna. This Section evolved to sustain bison, antelope, desert bighorn sheep, and deer, and extensive populations of lagomorphs and sage grouse. Grizzly bear, wolf, cougar, and coyote were the major predators. Bison, grizzly bear, wolf, and bighorn sheep were extirpated. Recently, desert bighorn sheep were transplanted in the Deep Creek Mountain Range, and elk were transplanted in the Canyon Mountain Range. Presently, there is a thriving population of antelope, and a scattered population of mule deer on mountain ranges. Cougar, coyotes, and bobcats have healthy numbers. There are extensive populations of black-tailed jackrabbits, desert cottontails, and pygmy cottontails. Isolated populations of sage grouse occur. The Section has also received transplants of non-native chukar and Hungarian partridge. There are many species of desert dwelling avifauna and scattered occurrences of reptiles. Historically, fish species included native fishes of Lake Bonneville, including least chub, Utah chub, speckled dace, Bonneville cutthroat trout, and Bonneville redside shiner. Most of these species exist now only in isolated pockets and most are trending toward extirpation. They are being replaced by introduced species such as rainbow trout, largemouth bass, and mosquito fish.

Climate. Precipitation averages 4 to 10 in (100 to 250 mm) annually; mountains receive as much as 18 in, annually. Precipitation is very low from summer to mid-autumn. Summers are hot and dry with low humidity, and winters are cold and dry. Temperature averages 45 to 55 oF (7 to 13 oC). The growing season ranges from 60 to 150 days.

Surface Water Characteristics. Great Salt Lake and Utah Lake are the major features of this Section. The water from the Beaver and Sevier Rivers is used for irrigation and seldom reaches the Sevier Lake. Nonetheless, the Sevier River is the major drainage that ends at Sevier Lake. Small streams drain the mountain ranges, and all areas have internal drainage. Ground water is scarce and has poor quality because of salts. Major streams that flow from other Sections into this Section include the Weber, Bear, and Provo Rivers; they eventually enter the Great Salt Lake. Clear Lake and Fish Spring are important water fowl management areas.

Disturbance Regimes. Common low intensity short duration burns of sagebrush and desert shrubs occur during summer thunderstorms. Often there is insufficient understory to carry fires, or they are suppressed.

Land Use. Military use occurs for purposes such as testing nuclear and armed forces training. Livestock production is an important use of the area. Some mining has also occurred.

Cultural Ecology. Reserved.

Compiled by Intermoutain Region.

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Section 341B--Northern Canyon Lands

Geomorphology. This area occurs within the Colorado Plateau physiographic province. Northern Canyon lands Section is located in the eastern portion of Utah. This area is eroded by the Colorado River and its tributaries. Deep sheer-walled canyons, canyonlands, lines of cliffs, low plateaus, mesas, buttes, and badlands dominate the landscape. Major landforms are the San Rafael Swell, Henry Mountains, Abajo Mountains, La Sal Mountains, and Circle Cliffs. Elevation ranges from 4,200 to 12,700 ft (1,300 to 3,900 m).

Lithology and Stratigraphy. Types include shales from the Cretaceous period, sandstones near Arches National Park from the Jurassic period, shales and sandstones from the Triassic period, and sandstones near Natural Bridges National Monument from the Permian period. Some eolian deposits occur on the central portion of this Section. Inclusions of diorites in the lacolithic mountains are present.

Soil Taxa. Entisols and Aridisols occur in combination with mesic, frigid, and cryic soil temperature regimes, along with ustic and aridic soil moisture regimes. Some soils are saline-sodic affected. Areas of very sandy and shallow soils exist. Higher elevations have Mollisols, Alfisols, and Inceptisols.

Potential Natural Vegetation. K\"uchler vegetation types are blackbrush, juniper-pinyon woodlands, saltbush-greasewood, and galleta-three awn shrub steppe. Areas of ponderosa pine series occur on the La Sal and Abajo Mountains. Areas of Arizona pine occur on the Henry Mountains. The Soil Conservation Service identifies the area as desert shrub and woodland vegetation with some big sagebrush. Spruce-fir forests with aspen occur on the higher elevations of the Henry, Abajo, and La Sal Mountains.

Fauna. This Section historically provided habitat for various species: desert bighorn sheep, bison, pronghorn antelope, and black-footed ferret in the lower elevations; mule deer, wild turkey, Rocky Mountain bighorn sheep, and elk at mid to high elevations; and river otter and beaver in riparian areas. These species, with the exception of pronghorn antelope and beaver, were extirpated through portions or all of the Section. Except the black-footed ferret, these extirpated species have been re-introduced. Large predators once included timber wolf, grizzly bear, black bear, cougar, bobcat, gray fox, and coyote. Timber wolf and grizzly bear have been extirpated. Wildlife species of the canyons include peregrine falcon, Mexican spotted owl, violet-green swallow, white-throated swift, woodrats (white-throated, bushy-tailed, and Mexican), ringtailed cat, spotted bat, rattlesnakes (midget-faded and Hopi), spadefoot toads (Great Basin and Mexican), collared lizard, and canyon tree frog. Desert shrub communities are characterized by prairie dogs (white-tailed and Gunnison), badger, kit fox, ferruginous hawk, turkey vulture, and burrowing owl. Bald eagles winter in lower elevations and a very few remain to nest along river corriders. Jackrabbits (black-tailed and white-tailed), Ord's kangaroo rat, mountain and western bluebirds, loggerhead shrike, red-tailed hawk, and Brewer's sparrow typify species of sagebrush and grasslands. Pinyon mouse, cottontail rabbit, white-tailed antelope squirrel, pinyon jay, and short-horned lizard are common species of pinyon-juniper woodlands. Forested areas provide habitat for Williamson's sapsucker, band-tailed pigeon, three-toed woodpecker, olive-sided flycatcher, pygmy nuthatch, and tiger salamander. Boreal owls are suspected at higher elevations near treeline. Riparian areas are used by many bird species, including yellow-breasted chat, lazuli bunting, northern oriole, and the rare southwestern willow flycatcher. Native fish species include the rare Colorado squawfish, razorback sucker, bonytail chub, humpback chub, and Colorado cutthroat trout.

Climate. Precipitation ranges from 6 to 30 in (150 to 760 mm) annually; most occurs during spring and fall. The climate is very dry and hot in the summer with low humidity, and cold and dry in the winter, indicative of a desertic condition. Temperature averages 45 to 55 oF (8 to 13 oC); higher elevations are colder. The growing season ranges from 60 to 180 days.

Surface Water Characteristics. Water is scarce. The area is drained by the Colorado and Green Rivers and their tributaries. Ground water supplies are limited. Summer rainstorms cause flash flooding in much of the Section. Few lakes and reservoirs occur. A small portion of Lake Powell occurs in the Section.

Disturbance Regimes. Common, low intensity, short duration burns occur due to thunderstorms. Water and wind erosion is also occurring.

Land Use. Grazing for sheep and cattle is the major land use. Hay and pasture land occur to a very limited extent along drainage ways. Recreation is also an important use.

Cultural Ecology. Reserved.

Compiled by Intermoutain Region.

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Section 341C--Uinta Basin

Geomorphology. This area occurs within the Colorado Plateau physiographic province. Unita Basin Section lies south of the Unita Mountain Range in northeastern Utah. It is a synclinal and topographical basin, with its east-west axis running near the south flank of the Unita Mountains. The central portion is gently rolling with eroded slopes. Elevation ranges from 6,200 to 7,300 ft (1,900 to 2,200 m). Local relief ranges from 100 to 1,000 ft (30 to 300 m).

Lithology and Stratigraphy. Sedimentary rocks from the Cretaceous and Paleocene periods, dominantly shales, sandstones, and siltsones, are dominant. Some glacial deposits occur on the northern portion of this Section. Alluvial and colluvial deposits occur in the center; some are old.

Soil Taxa. Entisols and Aridisols occur in combination with mesic and frigid soil temperature regimes, along with aridic soil moisture regimes. Many soils are saline-sodic affected.

Potential Natural Vegetation. K\"uchler vegetation types include juniper-pinyon woodlands and saltbush-greasewood. The Soil Conservation Service identifies some of the area as grasslands-shrub vegetation with some big sagebrush. Series include juniper-pinyon and saltbush-greasewood. Areas of big sagebush also occur.

Fauna. This Section is dominated by species typical of high, cold deserts. Mammals include white-tailed prairie dog, black-tailed jackrabbit, coyote, beaver, red fox, porcupine, spotted skunk, and Townsend's big-eared bat. It is year-round range for deer and antelope and winter range for elk. River otters were recently re-introduced, and their population appears to be increasing. Black-footed ferrets and bison occurred historically, but have been extirpated. Avifauna include waterfowl, wintering bald eagles, and an introduced population of Rio Grande turkeys along the Green River and its associated wetlands. Sandhill cranes and an occasional whooping crane occur during migration. The Green, White, and Duchense Rivers are thought to be important corridors for many neotropical migratory birds. The dominant desert shrub habitat is used by burrowing owls, short-eared owls, ferruginous hawks, sage sparrows, lark sparrows, western meadowlarks, loggerhead shrikes, horned larks, and occasional irruptions of lark buntings. Golden eagles nest throughout the Section. A breeding population of mountain plovers was recently documented here (representing an extension of their known range). Herpetofauna include the faded pygmy rattlesnake, striped whipsnake, and Woodhouse's toad. The Green River in this Section has been proposed as critical habitat for three endangered fishes endemic to the Colorado River system. Colorado squawfish, razorback sucker, and bonytail chub. It provides spawning habitat for the razorback sucker, and nursery habitat for all three species. The lower portions of the White River are also proposed critical habitat for the squawfish and razorback sucker. Two candidate fishes, flannelmouth sucker and roundtail chub, occur in the Green and White Rivers as well.

Climate. Precipitation averages 7 to 12 in (175 to 300 mm) annually; most occurs during spring and fall. It is very dry and hot in the summer with low humidity, and cold and dry in the winter, indicative of a desertic basin. Temperature averages 40 to 52 oF (4 to 11 oC). The growing season lasts 80 to 100 days

Surface Water Characteristics. Water is scarce. Some streams and rivers bring water into the area from adjoining mountains. Ground water supplies are limited. Major rivers that flow through the area are the Green, Duchesne, Strawberry, and smaller creeks that drain into the Green. Few lakes and reservoirs occur; examples are the Strawberry reservoir, Starvation reservoir, and Steinaker reservoir.

Disturbance Regimes. Few low intensity short duration burns of sagebrush occur due to summer thunderstorms. Most disturbance is from wind and water erosion.

Land Use. Grazing for sheep and cattle is the major land use. Hay and pasture land also occur to a very limited extent along drainage ways.

Cultural Ecology. Reserved.

Compiled by Intermoutain Region.

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Section 341D--Mono

Geomorphology. Isolated ranges of largely dissected block mountains are separated by aggraded desert plains (alluvial fans and basins). Elevation ranges from 4,000 to 14,200 ft (1,216 to 4,315 m). This Section is in the Basin and Range geomorphic province.

Lithology and Stratigraphy. Types include Cenozoic volcanic rocks and alluvial deposits, Paleozoic sedimentary and volcanic rocks, and Mesozoic granitic rocks.

Soil Taxa. Soils include Aridisols, Entisols, and Mollisols in combination with mesic, frigid, and cryic soil temperature regimes and xeric and aridic soil moisture regimes.

Potential Natural Vegetation. K\"uchler classified potential vegetation as sagebrush steppe, juniper-pinyon woodland, northern jeffrey pine forest, Great Basin subalpine forest, and alpine communities and barren. Potential natural communities include western juniper, pinyon pine, Jeffrey pine, basin sagebrush and bristlecone pine series.

Fauna. Pronghorn and mountain sheep were commonly found in the Section. Presently, pronghorn are limited to a few re-introduced herds and mountain sheep are found on a few high mountains. Mammals include mule deer, mountain lion, bobcat, coyote, jackrabbit, and chipmunk. Birds include eagles, hawks, northern goshawk, nighthawks, common poorwill, sage grouse, sparrows, and gnatcatchers. Mono Lake provides habitat to a wide variety of shore birds and migrating waterfowl. It is also the second-largest California gull rookery in the world. Sagebrush lizard, desert horned lizard, western fence lizard, and spadefoot toad are common.

Climate. Precipitation ranges from 10 to 25 in (250 to 640 mm). Temperature averages 39 to 50 oF (4 to 10 oC). The growing season ranges from 60 to 130 days.

Surface Water Characteristics: Few rapidly flowing rivers and streams occur. Rivers and streams flow in deeply incised canyons with bedrock controlled channels (higher elevations) to alluvial channels (lower elevations) that terminate in basins or lakes within the area, or in basins and lakes in the Mojave Desert, Bonneville Basin, or Northwestern Basin and Range Sections. Several large lakes occur within the Section.

Disturbance Regimes. Fires are infrequent, low, moderate, and high intensity surface or stand-replacing fires. This area contains locations with eruptive activity (lava flows and ash fall) within the past 200 years. This is a seismically active area with strong shaking and ground rupture.

Land Use. Composition and successional sequence of some communities have changed because of plant and animal species introduced between the mid 1800's and early 1900's related to mining, grazing, forestry, and recreational activities.

Cultural Ecology. Humans have been utilizing the Section for 10,000 years, and have been an integral part of its ecology for 3,000 to 5,000 years. Extensive prehistoric procurement and processing of obsidian resources have left vast areas pockmarked and littered with lithic debitage; extensive procurement and processing of piagi and pine nuts have modified vast areas of Jeffrey pine and pinyon. Historic mining booms beginning in the late 1800's and water diversion projects for the Los Angeles basin, beginning in the early 1900's, resulted in additional ecological modifications. Contemporary attitudes and beliefs emphasize amenity values. Human environment is characterized by a rural lifestyle of open space and out door leisure activity. Recreation is the primary economic emphasis, trailed by government employment, lumbering, mining, and grazing.

Compiled by Pacific Southwest Region.

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Section 341E--Lahontan Basin

Geomorphology. This area occurs within the Great Basin physiographic province. Lahontan Basin Section is located in the western portion of Nevada. Block-faulting created upthrusted north-south trending mountains which are interspersed with interior playas; surface water occurs frequently. Little glaciation is evident. Elevation ranges from 4,000 to 9,800 ft (1,200 to 3,000 m). Star Peak in the Humboldt Range is south of Winnemucca.

Lithology and Stratigraphy. Types include some Mesozoic granitics, but silicified sedimentary granitics predominate.

Soil Taxa. Soils include Mollisols, Vertisols, Entisols, Aridisols, Inceptisols, and Histosols. Mesic, frigid, and cryic soil temperature regimes predominate, along with torric, xeric, and aquic moisture regimes. Some saline-sodic soils are present; many soils are typified by hard duripans in the profiles.

Potential Natural Vegetation. K\"uchler vegetation types include saltbush-greasewood, big sagebrush, juniper-pinyon, aspen, marshes, and intermittent lakebeds with greasewood or little vegetation. The Soil Conservation Service identifies the vegetation as desert shrub with widespread shadscale. Areas of big sagebrush also occur.

Fauna. Camels, horses, and pronghorn antelope once characterized the Lahontan Basin Section. Today small herds of re-introduced antelope are found wintering in the lower elevations. Mule deer may be found in the pinyon-juniper and sagebrush zones. Coyote and bobcat are common. A variety of waterfowl use interior lakes. Wintering bald eagles are common on interior lakes. Avifauna is similar to what may be found in the sagebrush and pinyon-juniper zones in other parts of the Great Basin Province. Black-throated sparrow and sage sparrow typically inhabit the shadscale zone.

Climate. Precipitation averages 4 to 12 in (100 to 300 mm), increasing with elevation. It occurs primarily in the spring in the north and primarily in the winter in the south. The climate is very dry and hot in the summer with low humidity, and cold and dry in the winter, indicative of a desertic basin. Temperature averages 44 to 55 oF (7 to 13 oC). The growing season ranges from 80 to 152 days, decreasing with latitude.

Surface Water Characteristics. There are few perennial streams. Perennial waters consist primarily of the Humboldt River, headwaters of the Carson River, and interior lakes and marshes with no external drainage, typified by Humboldt Lake and Carson Sink. Occasional intense summer thunderstorms can produce massive runoff and flash flooding in the south end of this Section.

Disturbance Regimes. Fires are historically common due to thunderstorm activity. Large fires (1,000 acres or more) are common and moderately intense in the north end of this Section. Water and wind erosion also is occurring.

Land Use. Livestock production is the dominant land use, with some hay production in the major valley bottoms.

Compiled by Intermountain Region.

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Section 341F--Southeastern Great Basin

Geomorphology. This area is within the Basin and Range physiographic province. The Southeastern Great Basin Section is located in southern Nevada. North-south trending mountains are separated by broad sediment-filled valleys. Mountains are formed by faulting and modified by erosion. Large alluvial fans are at the mouths of most canyons. Elevation ranges from 4,700 to 9,400 ft (1,425 to 2,900 m). There are three or four peaks southwest of the Quinn-Canyon Range (in the Ely Ranger District of the Humboldt National Forest), which are at or close to 9,400 ft (2,900 m) elevation (e.g., Kawich Peak in the Kawich Range and Bald Peak in the Groom Range). These peaks are south and east of the southeastern-most end of the Toquima Range of the Toiyabe National Forest.

Lithology and Stratigraphy. Primary type is Lower Tertiary volcanic rock with Miocene volcanic rock. Valleys are filled with Quaternary deposits.

Soil Taxa. The dominant soils are Orthents, Psamments, Orthids, Argids, and Xerolls with mesic or frigid temperature regime, depending mostly on elevation. Some Aquolls occur in valley bottoms. Torriorthents and Torripsamments are on recent alluvial landforms. There are shallow to deep Camborthids, Durorthids, Nadurargids, Natrargids, Calciorthids, and Torriorthents, and shallow to deep Durixerolls, Haploxerolls, and Argixerolls in the mountains.

Potential Natural Vegetation. K\"uchler vegetation types include Great Basin sagebrush with some Great Basin pine forest and saltbush-greasewood. The Soil Conservation Service has classified the area as being desert-shrub, shrub-grass, and woodland vegetation. This area is a transitional zone between the mountains of the Toquima--Grant--Quinn Ranges, and the true Mojave (represented by Joshua tree cactus). Site factors (precipitation, soils, and topography) influence distribution of cholla chactus, greasewood and saltbush species, ephedra, sagebrush species, galleta grass, banana yucca, Fremont barberry, little leaf mahogany, Utah juniper, and single leaf pinyon; small amounts of limber pine, ponderosa pine, bristlecone pine, and subalpine fir.

Fauna. A variety of endemic fishes occur, including White River springfish, Railroad Valley springfish, White River mountainsucker, White River spinedace, Pahranagat spinedace, White River Colorado gila, and White River speckled dace. The Big Spring spinedace which once occurred here is now extinct. Desert bighorn sheep and pronghorn antelope live here. Nevada ring-tailed cats and two subspecies of kit fox live in the lowlands. Pallid bats, California myotis, western pipistrelle, and Mexican free-tailed bats range through the Section. Bailey's bobcat inhabits this Section, along with a variety of small mammals. round-tailed ground squirrel, cliff and Say chipmunks, Mohave long-tailed pocket mouse, Virgin River little pocket mouse, pallid kangaroo mouse, Merriam's and desert kangaroo rats, long-tailed southern grasshopper mouse, Stephen's canyon mouse, and the Arizona Audubon cottontail.

Climate. Precipitation ranges from 3 in (76 mm) at lowest elevations to over 20 in (510 mm) in the highest mountain ranges. Precipitation occurs mostly in winter months. Average annual temperature ranges from 52 to 60 oF (11 to 15 oC). The growing season ranges from 60 to 200 days, decreasing with elevation.

Surface Water Characteristics. There is very little perennial surface water. The headwaters of the White River (a tributary of the Colorado) are contained within this Section. Most other surface waters are intermittent, with internal drainage.

Disturbance Regimes. Infrequent, small to moderate, low intensity fires start due to thunderstorms. Fires remain small due to sparse fuels. Erosion by wind and water occur.

Land Use. Training and testing for the military and nuclear testing occur. Livestock production also occurs in this Section, along with some mining. Cultural Ecology. Reserved.

Compiled by Intermountain Region.

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Section 341G--Northeastern Great Basin

Geomorphology. This area occurs within the Basin and Range physiographic province. The Northeastern Great Basin Section is located in northeastern Nevada. There are north-south trending mountains with broad sediment-filled valleys, formed by thrust-faulting (e.g., south Independence Range). Some glaciation is evident on the highest peaks. Elevation ranges from 4,800 to 10,704 ft (1,500 to 3,250 m).

Lithology and Stratigraphy. Types include Mississippian, Ordovician, and Silurian quartzite, dolomite, chert, and Ordovician argillite and shale; and Devonian siltstones also occur.

Soil Taxa. Soils include Mollisols, Inceptisols, Entisols, Inceptisols, and Aridisols, along with a few Histosols. There are also Borolls, Xerolls, Fluvents, Orthents, Ochrepts, Umbrepts, Aquents, Aquolls, Fibrists, Hemists, Saprists, and Aquepts. These are identified through work done in the south Independence Range and the east Humboldt Range. These soils are associated with aridic and xeric moisture regimes, and mesic, frigid, and cryic temperature regimes.

Potential Natural Vegetation. K\"uchler vegetation types include Great Basin sagebrush and juniper-pinyon woodlands. Juniper-mahogany woodlands and aspen are also found.

Fauna. Small bands of bison once used the lowlands along the main river systems, but disappeared prior to white settlement. Marsh and riparian areas support rare Preble's shrews and a variety of shore birds and marsh-dwellers, including bobolinks. Lahontan cutthroat range into upper waters of this Section from mountain headwaters upstream, while the Lahontan redside shiner occurs throughout the Section. Endemic freshwater clams are found in the upper Humboldt River system. Richardson's ground squirrels and Nevada jumping mice are common.

Climate. Precipitation ranges from 8 to 30 in (200 to 760 mm), increasing with elevation. Average annual temperature ranges from 39 to 50 oF (4 to 10 oC). The growing season lasts from 50 to 125 days, decreasing with elevation.

Surface Water Characteristics. There are moderate to steep gradient perennial and intermittent streams, plus narrow flood plains. Some developed impoundments and a few cirque lakes are present. Many streams are diverted out of channel for irrigation.

Disturbance Regimes. Infrequent, moderate to large sized fires occur due to summer thunderstorms. Periodic catastrophic snowmelt in high snow years leads to debris flows down steep mountain valleys.

Cultural Ecology. Reserved.

Compiled by Intermountain Region.

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