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<br />O~1!)89 <br /> <br />Leadv i 11 e <br />Buena Vista <br />Pueblo <br />Lamar <br /> <br />18.6 inches <br />9.2 inches <br />II. 7 inches <br />15.4 inches <br /> <br />The maximum recorded temperature in the valley of 114 degrees F <br /> <br /> <br />occurred at Las Animas. Minimum telllperatures of -40 degrees F have <br /> <br /> <br />been recorded at several stations. The average growing seaSOn ranges <br /> <br /> <br />from approximately 90 days near the headwater reaches to 51 ightly <br /> <br /> <br />Over 180 days in the lower Arkansas Valley. <br /> <br /> <br />GeoloQY <br /> <br /> <br />The mountainous areas of the Arkansas River Basin consist pri- <br /> <br /> <br />marily of ancient granitic and metamorphic rocks, in addition to <br /> <br /> <br />Paleozoic sediments, Tertiary intrusive and extrusive rocks, Tertiary <br /> <br />sediments, and glacial lake and stream deposits. There is considerable <br /> <br /> <br />evidence of extreme folding and faulting. <br /> <br /> <br />The foothill area below the mountains Is composed primarily of <br /> <br /> <br />Cretaceous shale, chalk, limestone and sandstone and a certain amount <br /> <br />of volcanic rock. <br /> <br /> <br />The valley fill aquifer rests in a U-shaped trough cut into cretaceous <br /> <br /> <br />shale and lImestone bedrock. The trough was eroded by flows of the Ark- <br /> <br />ansas River. A commonly accepted explanation for the development of the <br /> <br />Ark.nlls VII ley Is (1) erosion of bedrock and the establishment of a <br /> <br /> <br />chlnnel or valley, (2) deposition of sand and gravel in the valley, (3) <br /> <br /> <br />repelted periods of erosion and deposition to form terraces, and (4) the <br /> <br />present flood plain depositi'ons. The valley fill aquifer consists of <br /> <br /> <br />gravel, sand, silt and clay of Pleistocene to Recent age. <br /> <br /> <br />~ <br /> <br />The soils in the Arkansas Valley can generally be divided into two <br /> <br /> <br />types: (1) those which occur along the river bottomland, terraces, and <br /> <br />benches, and (2) the uplands which are residual soils derived from shale, <br /> <br /> <br />I imestone, and sand.stone. <br /> <br />The majority of the soils in the valley are of excellent quality with <br /> <br /> <br />a topsoil varying from 1 to 2 feet in depth and a subsoil ranging from <br /> <br />5 to 20 feet. The depth of topsoil in the flood plain areas is extremely <br /> <br /> <br />variable as a result of erosion and deposition. The U. S. Bureau of <br /> <br /> <br />Reclamation estimates about two-thirds of the soils in the valley consist <br /> <br /> <br />of silty loam, c.lay loam and clay soils, and the remaining one-third <br /> <br />includes fine sandy loam or sandy soils. <br /> <br />- 6 - <br />