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114 CONTRIBUTIONS TO HYDROLOGY OF UNITED' STATES, 1923-1924. RORTll pon OF SEOSHon RIVU. The series of cloudbursts that ocCurred in northern W yorning during July culminated on the night of July 22 in a somewhat general rainfall covering a large territory.. Heavy rains in the mountains near Sylvan Pass caused a serious landslide 14 miles east of the eastern entrance to Yellowstone Park and stopped all traffic for two days, C. C. Spencer, forest ranger at Wapiti, gives the following descrip- tion of the storm: On July 19, 20, 21, and 22 we had a spell of unusually hot, sultry weather. In fact, it was about the worst I caD remember in this country during the past 18 years. The cloudbursts fo1\owed thia on July 22 and seemed to strike all of the high divides, as well as a few places lower down. Most of them struck . ne'll' or above timber line (about 10,000 feet elevation), The ten which struck. the North Fork of the Shoshone and its tributaries came between 6 and 8 p. om. They came down the following streams: Main North Fork, Grinnell, Gunbarrel, Clearwater, Blackwater, and Sweetwater creeks about 6- p. m., 'and Elk _:Fork~ Clocktower, Canyon, and Big creeks a1; 8 p. m. Canyon Creek carried the largest volume of water for the area drained, and the run lasted for more than an hour . Very little rain fell in the vaJIey, and the storm on the divides lasted but a few minutes. We have ;no records of precipitation. One thing I have noticed during the la.at few years is that these cloudbursts always come about the last of July and follow a period of hot, sultry weather.' Those this year (1923) were many tim.. larger and worse than any others of which I have knowledge in this section, . A map of the North Fork drainage basin shows that the creeks subject to the earlier cloudbursts were at a higher general altitude than those on which the cloudbursts occurred about 8 p. m; . The Bureau of Reclamation maintains a gaging station in sec. 15, T. 52 N., R. 104 W., 6 miles east of Wapiti, and the recording gage at that point showed that the river started to rise at 10 p. m., when its flow was 1,460.second-feet, and rose to a maximum discharge of 8,100 second-feet in a few minutes' time.. The period of crest. flow was equally short, and the river quickly fell again, althoJIgh it did not reach normal stage until noon of the following day (fig. 9, B). The almost instantaneous rise shows that the floods from both the upper and lower areas described above reached the gaging station at the same time, a condition which would cause the severest flood for that amount of rainfall over the basin, FLOOD OF SEFTEMBEB. 27-29, 1923. Heavy rains from September 27 to 29 covered the entire central and northern parts of the State and caused a flood on Big Horn River that wllSsecona in size only to that of July 23-24 at Thermopolis and exceeded it in the lower river. . . The following table shows all available Weather Bureau rainfall records in the Big Horn River drainage basin: