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discussion of the watershed runoff simulat'ion, using the MUDFLOW model is presented in Reference 2. Cornet Creek is a relatively small, steep watershed which experiences mud flows due to thunderstorms of short-durat i on and high - i ntens i ty. These storms may occur in the Cornet Creek basin without concurrent ra,infan on the town of Telluride. Measured data on the depth and distribution of rainfall within the watershed are not available. The development of appropriate estimates of the storm pattern which may induce a mud flQ','/ must, therefore, rely heavily on historical accounts of previous mud flow events. Estimates of precipitation for vaY'ious retu:en periods and a thunderstorm duration of one hour were developed from information in the Precipitation Frequency Atlas of the Western United States (Reference 3). From historic accounts of mud flows in Telluride, it is known that the duration of intense rainfall which has trig- gered the events is on the order of 30 minutes. Using the Rainfall Frequency Atlas of the United States, Technical Paper No. 40 (Reference 4), the ratio of precipitation depth for a 30-minute duration to I-hour duration rainfall is 79 percent. Development of rainfall hyetograchs was accomplished by distributing rainfall depths over a 30-minute period in accordance with a pattern suggested by the Bureau of Reclamation for a one hour thunderstorm (Reference 5). The resulting precipitation hyetographs agree with descript'ions regarding storm behavior from newspapers and eyewitness accounts in the Telluride area. To determine the excess rainfall from the Cornet Creek watershed the SCS curve number method in the HEC-I rainfall/runofF simulation model (Reference 6)"was utilized. The curve numbers upon which the method is based reflect the soil cover, type of Tand use, and antecedent noisture condition of the watershed. For the conditions described previously and an antecedent moisture condition III, a curve number of 91 was estimated for the watershed based on the descriptions and ranges of curve numbers presented in Appendix A of the pesigrLof Small Dams (Reference 5). The excess rainfall values determined through the HEC-I analysi s were used as input to the MUDFLOW watershed runoff simulation. The watershed was discretized into 69 grid elements on a 1:24,000 scale map with 40-foot contour intervals (Reference 7). Each element represents a I,OOO-foot square. Eleven of the elements were designated to contain the main channel in the watershed valley. Values for elevation and roughness were assigned to each element. Clear-water hydrographs from the watershed were developed for the 10-, 25-, 50-, 100- and SOO-year return period rainfall events. The probability of exceedance for a mud flow event is dependent on the combined probabi lit i es of exceedance for the ra 'i nfa 11, the ava i 1 abi 1 i ty of source material, and the antecedent moisture condition of the material. Complicating factors, which prevent an exact definition of mud flow frequency include the following: . Mud flows and mud floods have a wide range of potential sediment concentrations. The categories of mud flood and mud flow may vary between 20 to 50 percent sediment concentration by volume (Reference 8).