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remote Lawn Lake. Wayne Graham and Curtis Brown of the Bureau of Reclamation provided data on the flood traveltime and warning and response to the flood. Charles Huntley and Zenas Blevins, also of the Bureau of Reclamation, provided computation of the inflow to Lake Estes and hydrologic information. The U.S. Army Corps of Engineers, Omaha District, provided aerial photo- graphs that were taken 4 hours after the fl ood and were used to prepare topographic maps of the two lakes. Other valuable photographs in this report were obtained from the town of Estes Park, Federal and State agencies, and from private individuals. These photograph sources are credited in individual figures. The Setting Lawn Lake is a manmade enlarged natural lake, occupying a moraine-dammed depression on the southeast side of the Mummy Range in Rocky Mountain National Park (Colorado) at an elevation of about 11,000 ft (fig. 1). Local bedrock consists of Precambrian gneisses and schists that are more than 1. 7 billion years old (Peterman and others, 1967). Lawn Lake is fed by the Roari ng Ri ver, which originates upstream from Crystal Lake, a higher cirque lake about 1 mi upstream, at an elevation of about 11,500 ft. Downstream from Crystal Lake, the valley is steep and rugged. The Roaring River descends over a steep cliff into Lawn Lake. Downstream from Lawn Lake, a broad, till-covered valley extends southeast for about 0.5 mi; then the valley turns south. Slopes range from 5 to 26 percent, and average 10 percent along the Roaring River (fig. 2). Mean annual precipitation in the area varies with elevation, ranging from 20 in. at Estes Park to 40 in. or more on the Continental Divide above Lawn Lake. Downstream from Lawn Lake, the Roari ng Ri ver descends over a seri es of steep bedrock falls and through gentle mountain meadows. The Roaring River valley and the Fall River valley were repeatedly glaciated to the entrance of Rocky Mountain National Park during the Pleistocene Epoch. Landforms and sediments along the course of the flood bear strong imprints of this glacial activity (Jones and Quam, 1944; Richmond, 1960). Lawn Lake is at tree line; along the Roari ng Ri ver, vegetation cons i sts of spruce, fi r, and aspen for- ests. Where the Roaring River joins the Fall River at an elevation of 8,550 ft in the west end of Horseshoe Park, the Roaring River descends 500 ft in 0.3 mi in a series of rapids known collectively as Horseshoe Falls (fig. 1). Horseshoe Park is a fl at, morai ne-rimmed bas i n that was occupi ed by a large glacial lake when terminal moraines dammed the Fall River at the east end of the park. The hills surrounding Horseshoe Park are covered with ponderosa and lodgepole pines and aspen forests. The floor of Horseshoe Park is 0.5 mi wide and 3 mi long, and is underlain by ground moraine, outwash, and lacustrine sediments. Valley slope is relatively flat, averaging 0.7 percent. The park is covered by meadow grass; dense willows mark the meandering course of the Fall Ri ver through the park. Si nuos i ty of the Fall Ri ver in Horseshoe Park downstream from the Roaring River is 2.2, compared to 1.0 to 1.05 for other steeper mountain streams in Rocky Mountain National Park. 6