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II. Unit Description A. Physical Settinq The East River Unit is located in the Rocky ~1ountain Region, Gunnison National Forest, Taylor River Ranger District, Gunnison County, Colorado. It includes some 234,000 acres of Federal, State and private lands within its boundary. It is within the Southern Rocky Mountain Province and takes in portions of the Elk Mountains. The boundary proceeds from Almont up the T."Iylor River to Spring Creek, up Spring Creek and north to the cr'?St of the Elk Mountains, and along the crest west to the vicinity of Schoefield Pass. From Schofield Pass to Kebler Pass the boundary follows the crest of the Ruby Range through Angel Pass and over Purple Mountain to the Kebler Pass area. Southward from Kebler Pass, the boundary follows the divide along Mt. Axtell, Whetstone Mountain, Red Mountain and Flat Top Mountain. A large portion of the foothills of Flat Top Mountain are included as the boundary drops off the southwest sides of Flat Top and returns to Almont, Colorado, at the confluence of East River and Taylor River. Topography is generally mountainous throughout the unit. Rugged landscapes prevail in the northern portion, characterized by peaks to over 14,000 feet, steep slopes, rock outcrops, well defined avalanche paths and narrow V-shaped valley bottoms. Landforms appear highly dissected by drainages. Proceeding southward, mountain peaks are generally at elevations of 11 ,000 to 12,000 feet. Slopes become less precipitous and rock outcrops are less obvious. At 8,000 feet valleys broaden into fertile floodplains. Soils, tending to accumulate in place, support a wide variety of vegetation. The geology of the unit is very diverse. The entire East River Unit was influenced by the mountain building forming the Ancestral Rockies and the present Rocky Mountains. In places, Precambrian basement rocks are exposed where drainages have cut through the overlying sedimentary strata of limestone, shale, sandstone and conglomerate. In this area some important metallic minerals occur as weil as potential for geothermal resources. The northwest and western portions of the unit are characterized by Mesozoic and Cenozoic sediments. In many places they contain high amounts of Tertiary age intrusive materials which are the site of significant metallic mineral potential. Much of this portion of the unit contains potential for fossil fuel development in the form of coal and possibly gas and oil. Side slopes in this portion of the unit are made up of Mancos shale which is subject to high erosion and severe mass failure possibilities. Salls within the unit have developed from granites, gneiss, schist, sandstone, shale, limestone, conglomerates and glacial deposits. Because of this the soil types that have developed are numerous. As a general rule soils developing from the above parent materials in this area are low to moderate in fertility and moderate to high in erodibility. The topography in and surrounding the unit is responsible for a wide range of climatic variations occurring over short geographic distances. 3ased on data collected at Crested Butte, 1/ the average temperature is 32.5 degrees Fahrenheit. December, January, and February are the coldest months with an average Janu- ary temperature of 13.5 degrees Fahrenheit. Average July temperature is 58.0 degrees Fahrenheit and length of the growing season is 51 days. Temperature inversions are common during cold periods because of poor air drainage. Extreme low temperatures often occur in mountain park situations where air has stagnated. The principal preCipitation accumulations occur in winter and spring in the form of snow. Snowmelt begins ln May and is generally over by July except on high north slopes and at bases of avalanche runs. During summer, thundershowers are common and are occasionally accompanied by hail or sleet. May and October are the driest months. Precipitation levels range from 45 inches at the higher elevations to 23 inches at Crested Butte to approxi. mately 15 lnches at Almont. B. Bioloqical Setting 1. Veqetation The vegetation within the East River Unit Ct~ be broadly categorized into the follow~ ing cover types: 11 AppendiX L, Item 60. 9