<br />o
<br />'-l fans, Most soils in the study unit are deep, loamy,
<br />'.0 well-drained soils that are alkaline (Heil and others,
<br />~ 1977),
<br />Soils in the mountainous regions are (I) Cryolr
<br />oralf.~-rock outcrop soils, which are light-colored,
<br />wcll-drained soils that formed from weathering ofa
<br />variety of crystalline and sedimentary rocks and
<br />(2) Cryumbrepts-Cryochrepts-rock outcrop soils,
<br />which are dark- to light-colored, well-drained soils
<br />in the alpine areas straddling the Continental Divide
<br />(table 2) (Heil and others, 1977), Soils in the highest
<br />mountainous areas generally are medium to very
<br />strongly acidic,
<br />[n the nonmountainous areas, the most widely
<br />distributed soil association is the Cryaquolls-
<br />Argiboro Ils-Calciboro Ils-Cryboral fs-Cryoboro Ils-
<br />Torriorthentic-Haploborolls-rock outcrop soils, which
<br />generally are dark-colored, well-drained, moderately
<br />deep to deep soils, The Haplargids-Camborthids-
<br />Torriorthent~ association, which nmges in depth from
<br />shallow to deep, has light-colored, well-drained soil,
<br />and has fonned from weathering of in-place or locally
<br />transported sandstones and shales, The Haplargids-
<br />Natrargids-Calciorthids- Torriorthents association is
<br />deep, light-colored, well-drained soil formed from the
<br />weathering of sedimentary rocks and from eolian
<br />material. The soil association present at the lower
<br />altitudes is the Torriorthents, which ha.~ depths
<br />ranging from shallow to deep and is a light-colored,
<br />well-drained soil that fonned from [ocally weathered
<br />sedimentary rocks such as shales and sandstones,
<br />Soils in the nonmountainous areas generally are
<br />alkaline in nature,
<br />
<br />Ecoregions
<br />
<br />Ecological regions (ecoregions) have bcen
<br />established to characterize homogeneous areas on the
<br />basis of landscape features such as vegetation, soils,
<br />geology, physiography, and land use (Gallant and
<br />others, 1989), The study unit has been subdivided into
<br />five ecoregions: high-altitude tundra; low- to high-
<br />altitude forests; low- to middle-altitude semidesert
<br />shrublands; semidesert shtublands and wooded
<br />uplands; and salt deserts (fig, 6), The distribution of
<br />vegetation is determined primarily by mineral avail-
<br />ability /Tom soils and geologic materials and by
<br />amount of precipitation (Chaney and others, 1987),
<br />High-altitude tundra is characterized by a cold,
<br />humid to arid climate with vegetation above treeline
<br />containing low-growth shrubs, cushion plants, and
<br />forbs, Along the forest-tundra interface, there are
<br />sparse stands of Englemann spruce, subalpine fir,
<br />Limber pine, and Bristlecone pine, The middle- to
<br />
<br />high-altitude forests consist of Englemann
<br />spruce and subalpine fir; some areas are locally
<br />dominated by aspen, These forests vary from
<br />cool humid to warm dry climates depending on
<br />the altitude, In the low-to middle-altitude for,
<br />esrs, vegetation consists of aspen, Douglas fir,
<br />Ponderosa pine, Gambel oak, and Pinon pine-
<br />juniper woodlands,
<br />
<br />Low- to middle-altitude semidesert
<br />shrublands have a semiarid climate with vegeta-
<br />tion consisting of greasewood, four-winged salt,
<br />brush, shadscale, and sagebrush often
<br />interspersed with grasses, Semidesert shru-
<br />blands and wooded uplands are in a semiarid to
<br />arid climate, Sagebrush, rabbitbrush, and
<br />grasses grow in the semidesert shrublands, In the
<br />wooded uplands, vegetation consists of juniper
<br />and Pinon pine, grasses, and sagebrush, Salt
<br />deserts are arid and have vegetation consisting of
<br />saltbrush, greasewood, rabbitbrush, horse brush,
<br />and desert grasses, In the ecoregions classified
<br />as salt deserts and semidesert shrublands, non-
<br />native vegetation grows a.~ a result of agricultural
<br />activities in the area, Irrigated crops include
<br />barley, com, frui~ hay, oats, vegetables, and
<br />wheat (Chaney and others, 1987),
<br />
<br />Population
<br />
<br />The 1990 population in the largely rural
<br />Upper Colomdo River Basin was about 234,000,
<br />less than 10 percent of the total population of the
<br />State of Colorado (fig, 7) (Bureau of Census,
<br />1990), The largest population center in the study
<br />unit is Grand Junction (30,209), which is located
<br />at the confluence of the Colorado and Gunnison
<br />Rivers, Some other principal cities in the area
<br />include Delta (3,952), Glenwood Springs
<br />(6,841), Gunnison (4,762), and Montrose (9,306)
<br />(Bureau of Census, 1992), The larger cities in
<br />the basin are located predominantly near agricul-
<br />tural lands or in mountain recreational communi.
<br />ties, Population of many counties in the basin
<br />increased about 5 percent from 1990 to 1992,
<br />Eagle and Summit Counties had the largest
<br />increases, of about 12 and 13 percen~ respec-
<br />tively, Population totals are projected to increase
<br />for some of the counties (Delta, Eagle, Gunni-
<br />son, Montrose, and Summit) in the basin by more
<br />than 20 percent in the year 2000 (Colorado Divi-
<br />sion of Local Governments, 1994), Population
<br />in the basin for the year 2000 would be expected
<br />to exceed 300,000,
<br />
<br />ENVIRONMENTAL SETTING 11
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