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SECTION I ALAMOSA, COLORADO LOCAL PROTECTION PROJECT ~ I. DESCRIPTION OF STUDY AREA , A. General: Alamosa County, comprising an area of about 719 square miles, is located in the south central quadrant of Colorado (Plate 1). It is bounded on the south by Conejos County, on the north by Saguache County and on the west and east by Rio Grande and Costilla Counties respectively. Alamosa City is located in a broad, high mountain valley. This is the San Luis Valley, located in the south-central part of the state. Alamosa County is almost level and has an elevation of approximately 7,500 feet except for the extreme eastern part. The eastern edge of Alamosa County includes a small part of the Sangre de Cristo Mountain range and rises to an elevation of about 11,000 feet. Alamosa, which is located in a valley, is drained by the Rio Grande and its tributaries. B. Climate: The sun shines at least part of each day for 360 days a year, with an average temperature of 64.6 degress in July and 16.6 degrees Fahrenheit in January. Annual mean temperature is 41.9 degrees Fahrenheit. Average precipitation, including winter snows and summer showers, has been about five and one-half inches. The maximum 24-hour precipitation recorded at Alamosa is 1.78 inches. Average annual snowfall at Alamosa is 22.8 inches. During the winter months there is heavy snowfall in the upper mountainous area of the watershed. C. Stream Characteristics: The Rio Grande, one of the principal streams in the southwestern United States, is an interstate and international river. From its source on the eastern slopes of the Rocky Mountains in southcentral Colorado, the Rio Grande flows eastward for about 150 miles to Alamosa and then southward to the Colorado-New Mexico State line, through New Mexico and El Paso, Texas, where it becomes the International Boundary between the United States and Mexico. The river originates along the Continental Divide in the San Juan Mountain range at elevations generally above 10,000 feet. Along the Continental Divide, the river is fed by perpetual snow fields and springs. From its source until it reaches the Alamosa stream gage, the river drains approximately 1,710 square miles. The Rio Grande meanders through the San Luis Valley, a gently sloped plain surrounded by high mountain ranges. The San Luis Valley is about 100 miles long and about 60 miles wide. The valley is surrounded by the Sangre de Cristo Mountains on the east, the San Juan Mountains on the west, and the La Garita Mountains on the north. The Rio Grande is a perennial river. Streambed elevations within the study reach range from 7,538 feet at the upper end of the study reach to 7,525 feet at the lower end. II. HISTORY OF THE AREA Alamosa was founded on July 4, 1878, the date the Denver and Rio Grande Western (D&RGW) Railroad completed its rail connection from Denver to this site on the banks of the Rio Grande. Cottonwood trees lined the river, so they named the townsite "Alamosa", which means cottonwood in Spanish. Garland 3