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<br />Mountain, 13,232 feet, in the La Plata Mountains on the southern rim. See Plate 2 for locations <br /> <br />and Plate 3 for stream profiles. <br /> <br />5.3 Geology and Soils. The Dolores River is a tributary of the Colorado River Basin. Its <br /> <br />headwaters are in the San Miguel and La Plata mountains of the San Juan Range. The basin is <br /> <br />located in the cast-central portion of the Colorado Plateau physiographic province. The area is <br /> <br />characterized by northwest trending linear features (the Paradox fold and Dolores anticline). <br /> <br />which are deeply dissected by tributaries of the Colorado River. <br />The stratigraphy of the Colorado Plateau consists ofa Precambrian basement of igneous <br /> <br />and metamorphic rocks, follO\ved by a moderately thick sedimentary sequence of marine and <br /> <br />continental sandstones, shales, mudstones, and evaporates ranging in age from Cambrian to <br /> <br />Cretaceolls, igneolls rocks of Tertiary Age, and unconsolidated sediments of Quatcrnary Age. <br /> <br />5.4 Climate. The Dolores River Basin area is semiarid, and is characterized by lo\\' <br /> <br />precipitation and humidity. abundant sunshine, a fairly wide daily temperature range. and <br /> <br />moderate south to southwest winds. Typically. clear skies and relatively high elevation of the <br /> <br />area result in warm days and cool nights during the spring, winter, and fall. Maximum daytime <br /> <br />temperatures vary from about 32.40 degrees Fahrenheit in January to 80-90 degrees in July, with <br /> <br />corresponding nighttime minimums ranging from below 0 degrees to around 50 degrees. See <br /> <br />Table I below for a tabulation of average monthly temperatures. <br /> <br />8 <br />