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Of the land in the Town of pagosa Springs, 45.4 percent is residential and 8.1 percent is commercial. In Archuleta County, the land is 14.1 percent residential and /,5 percent commercial. The flood plain of the Town of pagosa Springs is partially developed, and some commercial development that will fall within the flood plain is planned. Some residential flood plain development is also planned in Archuleta County. .. The San Juan River, which flows through the Town of pagosa Springs, rises from the San Juan MountRins in southwestern Colorado and flows southwesterly. It join~ the Animas River at approximately the Colorado-New Mexico State line, A small tributary, McCabe Creek, enters the San Juan River from the north, in the west- central part of pagosa Springs. The Rio Blanco, which also originates in the San Juan Mountains, flows southwesterly and joins the San Juan River approximately 3 miles north of Truillo, Colorado. '. The drainage area of the San Juan River is approximately 298 square miles at pagosa Springs. The McCabe Creek watershed, which is a tributary to the San Juan River, covers approximately 20 square miles. The Rio Blanco watershed, which is also a tributary to the San Juan River, covers approximately 157 square miles at the down- stream end of the study area, The topography of the study areas in Archuleta County is primarily mountainous regions lying in the southernmost part of the state. The headwaters of the San Juan River start in the southern slopes of the San Juan Mountains at an elevation of approximately 13,000 feet and fall to an elevation of approximately 7,000 feet at pagosa Springs, which results in an average fall of an elevation of approx- imately 250 feet per mile. The headwaters of the Rio Blanco are at an elevation of approximately 12,000 feet and fall to an elevation of approximately 7,000 feet at the downstream end of the detailed study area. Through this reach, the Rio Blanco has an average fall of approximately 200 feet per mile. . The average annual precipitation in the study areas is approximately 20 inches, of which 8 inches is observed in the period from May through September. The annual mean temperature is 420F; the monthly mean temperature varies from 640F in July to 190F in January, Humidity is generally quite low, allowing rapid evaporation, . 2,3 Principal Flood Problems Major flooding along the San Juan River through Pagosa Springs usually occurs during the autumn and can be attributed to rainstorms of long duration. Minor flooding in the spring, at more frequent intervals, is caused by rapid snowmelt during abnormally 'warm weather. Localized cloudbursts during the sununer months have caused periodic flOOding of small streams in and around paqosa Springs and along the Rio Blanco River in Archuleta County. 5