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Creek, streambed slopes decrease at rates varying between 50 and 20 feet per mile. The slopes are conducive to rapid runoff and high channel velocities. In upper reaches, the channel ia well armored with rocks and boulders which resist erosion by normal flows. However, the swift currents inherent to flood discharges cause bank caving at about 5,000 c.f.s. The capacity of the channel between Long Csnyon and the mouth of San Francisco Creek is about 15,000 c.f.s. Floods originating in the watersheds of North and Middle Forks which form the Purgatoire River at their confluence are infrequent because of the impedance of the inflow of moist air by topographic barriers and the retardation of runoff by the coniferous forests and favorable ground cover. Much of the remainder of the watershed above Trinidad has been closely grazed for many years and the timber has been cut for mine props. In this condition, because of rapid concentration and high rates of runoff. it is the source of large magnitude flood discharges. The Purgatoire River above Trinidad is perennial, and the greatest volume of runoff is produced by melting of the snow blanket during April, May, and June. Summer thunderstorms, which are most active during July and August, produce floods with high peaks and relatively small volumes. Records indicate that hydrographs of floods resulting even from general storms are sharp with high peaks. Discharge records are available for 20 or more complete water years. The average annual water year runoff of Purgatoire River at Trinidad, Colorado, for 60 years of complete record. is 63.560 acre-feet; of this amount about 75 percent occurs during the period April through 11-4 . I I I I --1 .