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miles by 72 miles, which extends from near the foothills of the Rocky Mountains to the open plains of eastern Colorado, covering approximately 864 square miles. The climate in Arapahoe County varies slightly from the Denver metropoli tan area to the prairie' lands on the eastern end; but, generally, it is characteristic of the 'temperate high plains. The mean annual temperature is 50.2'F; the mean annual snowfall is 45 inches, and the mean annual rainfall is 14.05 inches. With a mean growing season of 139 days, agriculture flourishes. . Arapahoe County was the first designated county in Colorado even though at that time (1858), the county, which comprised over one- fifth of the present State of Colorado, was in the western part of the Kansas Territory. From then until April 1903, the county changed shape and size many times and on two occasions was nonexistent. Arapahoe County was visited by many explorers and trappers until gold was discovered at the mouth of Little Dry Creek, after which intensive growth was experienced throughout the region. The territory in and around Arapahoe County also became known as one of the greatest cattle ranch areas in the west. With the advent of the railroads, t$wns like Deer Trail became the natural termination points for cattle drives originating in Texas. Today, Arapahoe County is still basically an agricultural and resi- dential community, with most of the population concentrated in the western one-third of the county. During the past 25 years, the county population has grown rapidly as a result of Denver metropolitan area urbanization and subsequent extensive suburban development. County population figures for 1970 and 1980 are 161,000 and 293,621, respectively, This kind of suburban develop- ment pressure is now, and will continue to be, evident in and along the floodplains of Big Dry Creek, Little Dry Creek, Cottonwood Creek, Cherry Creek, Piney Creek, Sand Creek, Coal Creek, and the South Platte River. Residential growth has also occurred along the banks of Box Elder Creek and Comanche Creek. The county lies within headwaters extending into 14,000 feet. The waters appropriated for municipal River in Arapahoe County western edge of the county. the Sbuth Platte River Basin, with the Rocky Mountains to elevations of of the South Platte River have been and irrigation usage. The South Platte flows from south to north along the The South Platte River in Arapahoe County is a continuous flowing stream, whereas the tributaries are intermittent flowing streams. The South Platte River has two. major flooding characteristics-- snowmelt and summer thunderstormsi The tributary basins are narrow and have clayey-loam soils. In the undeveloped portions of the basins, the ground cover consists of buffalo grass, willows, and cottonwood trees. Development has occurred up to the channels on the tributaries. The floodplain on the South Platte, River in the past was mostly 6