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<br />0:1490 <br /> <br />. <br /> <br />(5) Relative humidity and evaporation. The area <br />is characterized by low relative humidity. The average annual evapora- <br /> <br />tion rate at the dam site will be about 67 inches. <br /> <br />d. Biotic communities. The Purgatoire River system <br /> <br />is associated with five life zones, or biomes. Descending generally <br /> <br />in a westerly to easterly direction these are: Arctic Alpine (12,000 <br />feet and above), Hudsonian (11,000-13,000), Canadian (8,500-12,000), <br />Transition (7,000-9,500), and Upper Sonoran (4,500-8,000). The <br />boundaries of these zones are not marked by continuous definite <br />lines but may vary up and down with topography, soil, and exposure. <br /> <br />Much overlapping and interfingering occurs. <br /> <br />e. Soil associations. Four soils groups found in the <br /> <br />Purgatoire River drainage area vary greatly in character. In the <br /> <br />upper or western part of the area above Stonewall, the Rough Stony, <br /> <br />and Alpine Meadow group are mostly of a complex of barren rough stony <br /> <br />land. In the meadows the soils are usually shallow and stony. From <br /> <br />Stonewall downstream to the front range below Trinidad, Lithosols <br /> <br />cover most of the area. The dominant types in this group are Under- <br /> <br />wood-Babb and McCammon-Deschutes. These soils are complex, as they <br /> <br />are developed on rough terrain from a variety of parent materials. <br /> <br />They are mostly shallow, stony, and lacking in very definite profile <br />development and subject to erosion. The Brown.soi1s are found in the <br /> <br />plains area. These soils are mostly silt loams, though there are also <br /> <br /> <br />some sandy soils. Alluvisl soils are found along the stream valley <br /> <br /> <br />and cover only a small portion of the area. <br /> <br />k.-- <br /> <br />. <br /> <br />II-7 <br />