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....,. .., ... . . . .. . . .. ........ .. .:,._~'-.__.~_h.. ... ~. INTRODUCTION A survey was conducted to determine the type and acreage of the phreatophytes along the flood plain of the Arkansas River in South- eastern Colorado. This survey was completed in accordance with the memorandum of agreement between the Bureau of Reclamation, Department of the Interior and Colorado State University (Contract No. 14-06-700-4747)' The purpose of this study was to determine oy survey the signifi- cant kinds and amounts of woody phreatophyte vegetation on the flood plain paralleling both banks of the Arkansas River from Pueblo, Colorado to the Colorado-Kansas State line. The portion of the Arkansas River Valley to which this survey was limited lies within the Colorado Piedmont section of the Great Plains physiographic province (Elkin, 1962). The major physiographic feature within the Colorado Piedmont section is the Arkansas River Valley. The valley extends eastward from Pueolo and ranges in altitude from 4,650 feet on the west to 3,350 feet (the lowest point in Colorado) at the Colorado-Kansas State line. Throughout this distance of approximately 150 miles the average fall of the river is 8.6 feet per mile. The Arkansas River occupies a broad, flat flood plain, which averages about 1 mile in width throughout the study area. The flood plain reaches a width of approximately 3 miles at the Colorado- Kansas border. The flood plain is bordered by flat terraces or alluvial plains lying aoove the river channel. Beyond the allwial plains and in some cases next to the river, sand hills WRY be found. The area north of the river is for the most part mantled or under- lain by unconsolidated sediments and is characterized oy broad, flat, valleys flanked by long, gentle slopes extending to the relatively flat drainage divides. The geologic formations exposed throughout the valley are primarily of Cretaceous age. A cross section of the formation in Prowers county is shown in Appendix III. The climate of the Arkansas River Valley in Southeastern Colorado is semiarid-continental. It is typical of similar areas within the Great Plains province of the same latitude but it is modified by the mountain barriers to the west. This area is subject to rapid changes in weather, particularly in the winter. The .,-inters are s110rt and have extreme variations in temperature. The swnmers are long and hot with cool nights. The average annual precipitation, as based upon records in excess of 50 years, ranges from 11.7 inches per year at Pueblo to 15.1 inches at Holly; however, most of the area -..:-.-.,..-:-...-. .