The sporadic but intense rains, known in the Southwest as cloudbursts, have in that arid and semiarid land extraordinary erosive power. Though cloudbursts occur frequently and their results are well known in a general way, accurate records of rainfall and detailed accounts of the work done by their ensuing floods are rare. Because of the present interest in floods in Los Angeles County, California, accurate records of the rainfall in a cloudburst on Rocky Gulch, in the San Gabriel Mountains, on April 4, 1926, are available and a description of the geologic results will be of interest to geologists. A number of papers on floods in the vicinity of Los Angeles and their control have already appeared.
The San Gabriel Mountains are a high, bold range, about 20 miles wide, that crosses Los Angeles County with a nearly east-west trend about 30 miles inland from the . . .