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<br />t.&J <br />-..J" <br />(0' <br /><0 <br /> <br />. <br /> <br />and Wyoming which might be regarded as humid islands in an otherwise <br /> <br />arid land. However, as the river progresses from its source to its <br /> <br />. <br /> <br />mouth acros s the arid plateaus of its drainage basin, the two proces ses <br /> <br />of salt loading and concentrating are accelerated. In the mountain head- <br /> <br />. <br /> <br />waters salinity levels are generally low because the rocks are hard and <br /> <br />the dissolving (or salt loading) process is slow. In addition, precipitation <br /> <br />rates are relatively high, so that the concentrating effects from evapo- <br /> <br />. <br /> <br />transpiration or consumptive use tend to be less than. is the case in the <br /> <br />arid regions of the basin. Quantities of dissolved solids within the waters <br /> <br />of the Colorado River increase with flow downstream. This increase is <br /> <br />. <br /> <br />directly related to the geologic character of the intervening terrain. In <br /> <br />the mountainous area.s a close relationship exists between the groundwater <br /> <br />. <br /> <br />in the consolidated rocks and allu"l1ium and surface waters. Residual <br /> <br />waters from rain and snowmelt ultimately reach the surface stream sys- <br /> <br />tem by way of springs, seeps, or through the alluvium along stream beds. <br /> <br />. <br /> <br />As the stream level rises and falls, water alternatively moves from the <br /> <br />stream into the alluvium and back again resulting in the dissolving and <br /> <br />. <br /> <br />transporting of salts. In the lower drainage areas of the Basin there <br /> <br />are large areas of shallow shale deposits where the salts are readily <br /> <br />dissolved by water movement across or through the soil profile. These <br /> <br />. <br /> <br />dissolved salts in turn, are tra.nsported by the river systems by sub- <br /> <br />surface flow in the underlying geologic formations. <br /> <br />The s e natural <br /> <br />8 <br /> <br />. <br /> <br />. <br />