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<br /> <br />generated by municipal and industrial discharges <br />and storm-water runotT. <br /> <br />Downstream of the Front R.ange, the South Plane <br />River and nearby alluvial aquifers support extensive <br />irrigated agriculture. The river is heavily diverted <br />and successively re-used, thereby acquiring relatively <br />high levels of salinity and nutrients. <br /> <br />Upper Colorado Basin <br />Dl:filled as il/elud;ng al/ tile Ju'adll'aters tributaries alld tile <br />ma;/I stem d,IWIlstrcam to the Grand Val/ey, indlldiflg the <br />Ya/llpa, 9r('('fI a"d H1titc rivers. <br /> <br />The upper Colorado comprises the most mountain- <br />ous area of the state ,md has only about 7 percent of <br />the population. <br /> <br />Of the many mining districts in the headwaters of <br />this basin, very few create water-quality problems. <br />Notable exceptions include the Montezuma, <br />Gillilan and 13reckenridge districts. <br /> <br />The development of mountain ski and golf <br />resorts-associated with Ilutrient loading and sedi- <br />ment development-threaten existing high-quality <br />waters in numerous headw;lters areas. <br /> <br />Generally high-quality aquat- <br />ic ecosystems, including <br />many gold-medal fisheries, <br />exist in the upper Colorado <br />basin. <br /> <br />Federal lands (Forest Service <br />and Bureau of Land Manage- <br />ment) dominate the upper <br />basin land-ownership pattern. <br />These lands are used for a <br />variety of purposes (grazing, <br />timber harvest and motorized <br />recreation) that may cause <br />localized erosion and sedi- <br />mentation to streams. <br /> <br />Lower Colorado Basin <br />Defined as the main stem in the Grand Ullley to the Utah <br />border, indudit~~ tlte Gunniso/l RilJCr and tributaries jlowifl~~ <br />out of the state h~{orc emptyi1lg i1lto the Colorado RilJCr, stich <br />as the D%res and Satl juall rivers. <br /> <br />The lower Colorado basin comprises about 18 per- <br />cent of the state's surface area and has 4 percent of <br />the population. <br /> <br />As in the upper basin, federal lands managed by the <br />U.S. Forest Service and the Bureau of Land <br />Management dominate the land-ownership pattern. <br />In fact, 47 percent of the entire Colorado basin in <br />the state is public land. These lands are used for a <br />variety of recreational activities and resource-extrac- <br />tion and development purposes that may cause non- <br />point source pollution to streams. <br /> <br />The headwaters of the Animas, Uncompahgre, San <br />Miguel and Dolores rivers originate in a highly <br />mineralized area of the San Juan Mountains. A cen- <br />tury of mining has led to impaired segments in all <br />of these river systems. <br /> <br />Intensive agriculture on areas of naturally occurring <br />saline Mancos shales contributes to salinity and sele- <br />nium loading in the Colorado River basin. <br /> <br />63 counties <br />ref, <br />~Q locally-based. ~ sOh <br />O"e:( ~te~L s o?erate In COlOrado CXu\ters underlie 0 e's surface area. elYon <br />lied OUtreach l10ljQ 60s'(). Ver 24% of the stat grOUnd water' <br /> <br />';..0<7> <br />GO <br />