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<br />1\1" n ,.." IlP r= : <br />-.. .'. \.1:" y ;.1 ~I <br /> <br />floods are nonexistent on the canyon floor, but great <br />variations ill releases by impoundments can result in <br />very high seasonal and daily fluctuations. Extremes <br />have measured from over 10,000 cubic feet per second <br />(cfs) - in the high run-off years of 1983-84 - to a <br />minimum of 200 cfs, with average flows ranging from <br />1600 to 2000 cfs. Silt and driftwood content are very <br />low L€caus~ of the impoundments. The fluctuations do <br />impact the river strand, the gravel and sand bar <br />configuration and the fishery habitat, however no data <br />is available on the morphology or ecology of'the river, <br />since the cessation of natural flooding. The river <br />flood plain is narrow, in some places nonexistent, and <br />typical of an actively down-cutting, youthful stream. <br /> <br />5. Geologic Process and Conditions <br /> <br />The Gunnison River is still actively down-cutting the <br />Black Canyon. Uplift has ceased and the main geologic <br />processes are those of weathering and erosion. The <br />dominant rocks are Precambrian metamorphic and igneous, <br />which are very resistant to erosion. Some sedimentary <br />rocks form minor ridges, particularly on the North Rim. <br />Rim soils are thin and acidic with much exposed <br />bedrock. The North Rim walls are nearly-vertical, bare <br />bedrock, while the South Rim, with a gentler slope and <br />more side canyons, has areas of thin soils. The canyon <br />floor has alluvial soils at the mouths of the side <br />canyons and scattered along the main stream where <br />backwater deposits occur. They support a river strand <br />rich with vegetation. <br /> <br />6. Wildlife <br /> <br />The wildlife of the monument is typical for the <br />geography and elevations of the region. Large mammals <br />include mule (black-tailed) deer, black bear, migrating <br />elk and an occasional cougar. Bighorn sheep were <br />reintroduced on BLM lands to the west of the monument <br />in 1985 and the herds have been regularly observed in <br />the monument. River otter were also reintroduced <br />outside of the monument and are frequently seen in the <br />monument. Small mammals are represented by a variety <br />of rodents including a relatively large population of <br />porcupines. <br /> <br />The topography has attracted a significant raptor <br />population including golden eagles, bald eagles, <br />prairie falcons, peregrine falcons, and many migrating <br />birds of prey. A substantial population of swifts and <br />swallows favors the steep walls as nesting sites. <br /> <br />9 <br />