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<br />. <br /> <br />I <br />"\J <br /> <br />PART III COLORADO RIV::R BASIl! <br /> <br />(2) . Quali tv <br /> <br />The quality of surface water in the Colorado River Basin <br /> <br />is generally good in all six subbasins. Excellent quality is <br /> <br />~enerally to be found at the headwaters of the subbasins. <br /> <br />Degradation of the chemical, physical. and biological quality <br /> <br />is evident as streams pro~ress downward, resulting from hydro- <br /> <br />logic, geologic, and manmade influences. <br /> <br />(a) Chemical - Wide variations in the mineral quality <br /> <br />of water may be noted in individual streams within the basin. <br /> <br />Dissolved solids concentrations in streams located high <br /> <br />.' <br /> <br />\ .,) <br /> <br />111 th~ "lfluUH l:.a.inci illi:iY be: <br /> <br />less ti!cfl :2~ <br /> <br />." <br />III~,' ..1... <br /> <br />, _! , ": :: -- .-.--" <br />\111.............5............... <br /> <br />...-- <br /> <br />liter). In contrast, a few streams at lower elevations <br /> <br />bave levels of dissolved solids exceeding 2,000 to 3,000 <br /> <br />mg/l. during certain times of the year. <br /> <br />The pattern of increasing mineral concentrations in <br /> <br />the downstream direction is largely due to the ty?e of <br /> <br />rocks.underlying the drainage basins. While the stream's <br /> <br />headwater areas are chiefly underlain by igneous and <br /> <br />metamorphic rocks, their middle and lower reaches are <br /> <br />often undf:!rlain by sedimentary rocks which contain more <br /> <br />soluble minerals. <br /> <br />Wide variations in ion concentrations are also found <br /> <br />. <br /> <br />,. <br /> <br />within the basin. Headwaters areas yield predominantly <br /> <br />-rD.. - / 'J <br /> <br />-1 <br /> <br />\)~\., <br /> <br />T <br /> <br />./ <br />