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DESCRIPTION OF BASIN Q c:n -..1 "n are reddish brown in color and have lying formations or adjacent areas. soils, but in many areas topogra;phy no resemblance to either the under- These are excellent agricultural makes agriculture difficult. C. Climate The Colora'lo River Basin has climatic extremes, ranging between year-round snow cover and heavy precipitation on the high peaks of the Rocky Mountains to desert conditions with very little rain in the south- ern part of the basin. This wide r8-Qge of climate is caused by differ- ences in altitu'le, latitude, and by the configuration of .the high moun- tain r8-Qges. The encircling mountain ranges o~struct a~d deflect the air m'3.sses to such an extent that storm ;:>atterns are more erratic than in most other parts of the United States. Most of the moisture for pre- cipitation on the Upper Basin is derived from the Pacific Ocean and the Gulf of Mexico. T1le Pacific source predominates generally from Octo~er through April and the Gulf source during the late spring a:.1d ea!'ly SUrmner. In the n::Jrthern part of the basin most precipitation falls in the form of winter snoWS a:.'li spring rains. Summer storms are infrequent but are sometimes of cload.b-JX'st intensity in localized areas. In the m)re arid soathern portion the principal rainy season is in the winter months with occasional localized cloudbursts in the su~er roll fall. Extremes of temperature in the basin r8-'lge from 500 F. below zero to 1300 F. above zero. The northern po~tion ::Jf the basin is characterized by short, warm summers and long, cold winters, and cwny mO'J.ntain areas are blanketed by deep snow all winter. 1>1e southern p::J~ion of the basin has long, hot s\L'llI1lers, practically continuous sanshine, and almost co:n- plete absence of freezing temperatures. Nevertheless, the entire ~asin is arid except in the extremely high altituies of the headwaters a!'eas. Rainfall averages as low as 2.5 inc:hes in the southern end. of the basin while total precipitatio!l in the high moantains may range from 40 to 60 inches annually. D. Vegetation Areas of higher elevation are covered with forests of pine, fir, spruce, and silver-stemned aspens, broken by small glaies and moantain meadows. Pin::Jn a:.1d jlmiper trees, intersperse.l with scrub oak, mountain mahog8-QY, rabbit bl'ush, .bLillCh grasses, and similar plants grad' in the intermediate elevations of the mesa and plateau regions. Large areas in the upper Basin are d~minated by big sagebrush aQl related .vegetatio!l. Many of the streams are bordered by cottonwoods, willows, a~d salt ced~r. 9