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<br />fisheries. Downstrean, land use is dominated by intense agricultural <br />activity. The topography of the plains is gently to moderately rolling <br />with elevations from about 7000 feet along the foothills in Colorado and <br />Wyomi ng to about 1870 feet at Grand. Isl and, Nebraska. These 1 ands <br />and surrounding areas provide important habitat for a variety of birds <br />and smaller animals. The streams, sandpits, ponds, and lakes across <br />Nebraska and in eastern Wyoming and Colorado provide warm-water fish <br />habitat. <br /> <br />Natural formations of significant aesthetic value exist in the study <br />area. The scenic vi stas of the Rocky Mountains and the unique attrac- <br />tions of the mainstem habitat reach highlight these values. The study <br />area is also historically rich with important pioneer migration routes, <br />railroad developments, settlements, outposts, and mining encampments <br />scattered throughout. <br /> <br />Other than the South Platte River, the mainstem Platte River has no <br />principal right-bank or southern tributaries. One of its left-bank <br />tributaries, the Loup, joins the Platte River at Columbus, Nebraska, <br />and thus helps to define the lower point of the study area. <br /> <br />Because of the diverse topography, a wide variety of climatic conditions <br />exist. In general, average annual precipitation increases from about <br />10 inches in the western part to about 24 inches in the eastern part. <br />The high mountains of Colorado and Wyoming are exceptions; precipitation <br />in these areas averages as much as 40 inches, most 1 y in the form of <br />snowfall. In the lower portions of the study area, precipitation is <br />more uniformly spread throughout the year. Winters are marked by snow <br />and at times blizzard-like conditions; springs and summers are marked by <br />occasional showers and thunderstorms with some incidence of severe <br />weather with wi nd and hai 1. <br /> <br />January is normally the col dest month of the year and July the warmest <br />in terms of average temper atures. The average frost-free peri od <br />generally ranges from 120 days in the west to 160 days in the east. <br /> <br />Socioeconomic Characteristics <br /> <br />Several primary socioeconomic characteristics are important to an <br />adequate description of the study area. Population, income, employment, <br />and major industrial sectors are briefly described to gain an under- <br />standing for what presently occurs in the study area. For purposes of <br />this analysis, the Upper Platte River Basin includes 7 counties in <br />southeastern Wyoming, 18 Colorado counties located along the eastern <br />slope of the Rockies and northeastern portion of Colorado, and <br />18 counties in southwestern Nebraska. <br /> <br />Popu 1 at ion <br /> <br />The population of the Upper Platte River Basin has <br />steadily over most of the 49-year period, 1930-1978. <br />to thi s occurred in the 1930' s when a 1 arge dec 1 ine <br /> <br />been increasing <br />The exception <br />wasexperi enced <br /> <br />6 <br />