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The Animas River's upper drainage basin (near Hermosa) is bounded by the Dolores and San Miguel River basins on the west; by the Uncompah- gre and Gunnison River basins on the north; and by the Rio Grande, Los Pinos, and Florida River basins on the east. Elevations range from approximately 6,700 feet in the Hermosa area to over 14,000 feet in the highest headwater areas of the Animas River and 11,000 feet in the Hermosa Creek basin. Soils of the study area are mostly Rock Outcrop-Cryumbrepts associa- , tion according to the u.s. Soil Conservation Service's classifications. These soils are shallow and well to poorly drained; therefore, they have slow infiltration rates when thoroughly wetted and a slow rate v of water transmission. Most of the watersheds are covered with trees and bushes which tend to reduce the runoff potential. The climate of the study area is arid to semi-arid except in the high headwaters, where precipitation is moderately heavy. The Durango area has a mean annual precipitation of approximately 18 inches, with 8 inches falling from May to September. The areas at Bayfield and Ignacio have a mean annual precipitation of approximately 14 inches, with 6 inches observed from May to September. The Vallecito Reservoir area receives 25 inches mean annual precipitation, with 10 inches of this in May through September. The mean annual temperature in the study area is approximately 450F, which varies from 660F in July to 2loF in January.. The humidity is generally quite low, which allows rapid evaporation in all the study areas. 2,3 Principal Flood Problems Generally, severe floods are caused by rainfall in the study area. General rainstorms usually occur during the period from July through October. This type of flood results from prolonged heavy rainfall over the watershed and is characterized by peak flows of moderate volume and duration. Flooding is more severe when antecedent rain- fall has saturated the soils in the watershed. Flood potential also exists from the rapid melting of heavy snow cover in the late spring. Floodflows resulting from snowmelt are characterized by moderate peaks, large volume, and long duration. This type of flood is usually not as damaging as those resulting from general rainstorms. ~ Cloudburst storms generally cause flooding on the streams having small tributary areas. These high-intensity, short-duration type rainstorms usually occur during the summer. Floodflows resulting from cloudburst storms are characterized by high peak flow, short duration of flow, and small volume of runoff. . Information on flooding in the Durango study area prior to the turn of the century is practically nonexistent. Detailed information on the earlier historical floods is very limited because streamflow records were not made, newspaper accounts were very sketchy, and eye-witness accounts are not available. Large floods occurred in 1896, 1909, 1911, 1927, 1937, 1941, 1946, 1949, 1970, and 1972. 5