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The plains constitute approximately two-thirds of the county, with a gentle west-to-east dip from 5,300 feet to 4,300 feet in elevation. The City of Pueblo; Town of Boone; the unincorporated communities of Pueblo West, Blende, Salt Creek, and Avondale; and the areas known locally as the St. Charles Mesh and Vineland, are all located on the plains (Reference 8). The St. Charles River originates near San Isabel, Colorado, on the northeast face of the Wet Mountains. It covers a stream distance of approximately 50 miles before its confluence with the Arkansas River. In the study reach, the river has eroded into shale and limestone strata deposits during the Cretaceous Age to form a narrow, entrenched valley within surrounding high plains. This valley is bordered by bluffs that seldom exceed 30 feet in height. Valley widths range from approximately 1,200 feet in the upper study reach to 3,000 feet near the river's mouth, with some isolated segments narrowing to as little as 600 feet. Approximately 67 square miles of the upper watershed is above 9,000 feet in elevation. Greenhorn Mountain and St. Charles Peak, at elevations of 12,349 and 11,738 feet, respectively, are in this region. The streambed elevation at the mouth is approximately 4,545 feet. Stream slopes are relatively steep, averaging approximately 20 feet per mile through the study reach. The total watershed covers an area of 482 square miles. The study reach lies primarily in the lower short-grass plain zone where native blue grama and galleta grasses with some rabbit brush are found. Cottonwood, willow, and tamarisk (salt cedar) are the predominant trees growing along the channel banks. The upper watershed vegetation consists of mixed conifers, such as pine, fir, and spruce, and typically contain grasses including side-oats grama, needle, Arizona fesque, and mountain muley. The river is a typical perennial mountain stream sustained by runoff from snowmelt and rainfall in the late fall, winter, and early spring. Runoff increases and flooding occurs during the summer months in conjunction with increased thunderstorm activities. The average annual precipitation varies from about 12 inches at the mouth of the stream to 24 inches in the upper elevations of the watershed. In recent years, urbanization has gradually expanded into the lower valley to occupy some floodplain lands that were formerly used for agriculture purposes. Most of the new construction, primarily residential, is located in the vicinity of Ford Lane, U.S. Highway 50, or 27th Lane. This development is gaining momentum, but agriculture and stock-grazing activities remain dominant (Reference 1). The Fountain Creek watershed is approximately 65 miles long and a maximum of 25 miles wide. The total drainage area is approximately 4