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. ... <:> <:> "" . . DESCRIPTION OF BASI~ B. Soils The soils of the Colorado River Basin closely resemble the geologic formations of their origin. Only in limited areas at the higher eleva- tions has the precipitation leached the soil mass of its soluble constit- uents. Over most of the area both residual and transported soils are basic in reaction and ....ell supplied with c.lrbonates with normal or rn.:Hure soils exhibiting a distinct horizon of carbon;lte accumulation. The im- press of !Dil-forming factors ms resulted in a \..!ide ran~e of soil development. Soils formed in areas with low precipitation are classified in the orders Entiools and Aridisols. Those formed in areas with high precipitation are classified in orders ~ollisole and Alfisols. Saline and alkali (sodie) so11s occur in many parts of the basin. The residual soils comprise the larger area and are usually shallow in depth over shale and sandstone of various ages. Many of the shales ar~ &1line but contain much gypsum as well as other chloride and sulphate salts. Some formations are high in sodium chloride and some have sodium carbonate or bicarbonate strata. Very few residual soil areas are suit- ahle [(lr irrigation development. A large part of the salt pickup occurs in areas ""here the natural runoff contacts the saline shales before entering the streams. The alluvial materials are extremely variable and ran~e from allu- vial fans and terraces, outwash plains, to lacustrine sediments. Some areas Iklve soils from material transported only shor t distances and re- semble the original materiills. Other areas have soils which have been transported and mixed extremely well. Most of the agricul tural areas are on these well-mixed alluviums and, therefore, the soils are quite variable. Extensive areas of Eolian deposits occur in parts of the basin, principally in southwestern Colorado. The uniformly textured soils are reddish brown in color and have no resemblance to either the underlying formations or adjacent areas. These are excellent agricultural soils, but in many areas topography makes agriculture difficult. C. Climate The Colorado River Basin has climatic extremE's, ranging between year-round snow cover and heavy precipitation on the high peaks of the Rocky Mountains to desert conditions ....ith very little rain in the south- ern part of the basin. This .....ide range of climate is caused by differ- ences in altitude, latitude, and by the configuration of the high mountain ranges. The encircling mountain ranges obstruct and deflect the air masses to such an extent that storm patterns are more erratic than in 11