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<br />w <br />(X) <br />Nt <br />....... <br /> <br />. <br /> <br />This strange and marvelous relation of water and land which has <br /> <br />etched out the basin over geologic time has much to do with the qualities <br /> <br />. <br /> <br />of water in the basin. <br /> <br />Basin Ph'Jsical Characteristics <br /> <br />The following descriptions provide an overview of the physical set- <br /> <br />. <br /> <br />ting which affects Colorado River quality. <br /> <br />Climate. The climate of the Colorado River Basin is one of wide <br /> <br />. <br /> <br />extremes. This is due to the wide variation in topography and the range <br /> <br />in latitude covered by the total basin. <br /> <br />The climate is associated with air masses moving in from either <br /> <br />. <br /> <br />the Pacific Ocean or the Gulf of Mexico. The Pacific air masses moving <br /> <br />inland are associated with winter precipitation while summer thunder- <br /> <br />. <br /> <br />storm activity moves in from the Gulf of Mexico. The northern portion <br /> <br />of the basin is occasionally affected by Canadian Arctic air during the <br /> <br />winter period. <br /> <br />. <br /> <br />Precipitation in the Colorado River Basin is str ongly affected by <br /> <br />the topography and supply of moisture. Moisture carrying air mas ses <br /> <br />must travel considerable distance and cross several mountain ranges <br /> <br />. <br /> <br />before the basin is reached. Thus, in general, precipitation is limited <br /> <br />except in th" high mountain regions. Annual precipitation varies from <br /> <br />. <br /> <br />6 inches or less in the lower valleys and southwestern region of the <br /> <br />basin to 50 inches or more in the highel mountains. In most of the <br /> <br />Lower Basin and southern areas of the Upper Basin, which are classified <br /> <br />. <br /> <br />2 <br /> <br />. <br />