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Streams in mountain sections are swift flowing;, with slopes vary- <br />ing from 20 feet to 1,000 feet per mile, The average gradient of the <br />South Platte from its mouth to Denver is about 8 feet per mile, and it <br />increases to about 70 feet per mile above Denver. All streams of the <br />South Platte originating in mountains are perennial; those beginning in <br />the high plains are intermittent. Principal tributaries are presented <br />in table 20 The mean annual recorded runoff of the South Platte River <br />at North Platte, Nebraska, is approximately 3809000 acre -feet. <br />Table 20 South_ Platte River Basin - Princa.p�1 tributaries of the South <br />Platte River <br />Tributary <br />Length <br />stream <br />(miles <br />Drainage Area <br />(square <br />miles) <br />Source <br />elevation <br />(feet) <br />Bear Creek <br />44 <br />265 <br />12,740 <br />Cherry Creek <br />- <br />414 <br />7630 <br />Clear Creek <br />67 <br />600 <br />12,200 <br />St. Frain Creek <br />61 <br />1,000 <br />129400 <br />Big Thompson River <br />79 <br />8/+2 <br />119000 <br />Cache la Poudre River <br />121 <br />1,840 <br />10,700 <br />Crow Creek <br />110 <br />1,515 <br />8,600 <br />Lodgepole Creek <br />216 <br />3,100 <br />8,500 <br />A variety of climatological conditions exists throughout the <br />Basin. Recorded extreme temperatures show highs in excess of 1000 F., <br />and lows of about -/.00 Fe The average growing season at Denver is 163 <br />days, at Boulder 165 days, and 145 days at Julesburgo The relative <br />humidity of the region is low, averaging less than 60 percent at Denver. <br />`'he entire Basin lies within a semiarid region with rainfall averaging <br />about 15 inches. Maximum precipitation occurs in the mountain area and <br />the minimum in the high plateau section. Average rainfall at hartsel is <br />11.1 inches, that at Greeley 12.35 inches. Precipitation at Silver Lake <br />in the mountains is 31 inches. <br />The mountains provide a great deal of mineral wealth, primarily <br />lead, silver, gold, zinc and coal. There has been a recent increase in <br />producing oil wells in the plains section and numerous gas wells exist <br />in the lower valley. <br />Silt carried by numerous mountain streams has formed rich alluvial <br />plains where those streams emerge from the mountains. here, intensive <br />agriculture is practiced when sufficient irrigation water is available. <br />The lumber industry has a rich source of material in coniferous forests <br />which cover the mountains. ivbuntains, forests, and waterways form a <br />scenic wonderland which has resulted in "Colorful Colorado" being called <br />the playground of America. <br />11 <br />