WATER 191 



cut loose on the debris in February of 1927 and this reservoir all but filled 

 with silt and boulders within a month. 



On New Year's Day, 1934, newspapers the country over cried of ruin in 

 the pleasant suburban communities of La Crescenta, Verdugo, Montrose, 

 and La Canada, just north of Los Angeles. Torrents of water, mud, and 

 boulders swept down from mountains killing 34 people and demolishing 

 400 homes. The disaster, wrote Charles J. Kraebel, reviewing causes, clearly 

 indicated a "fatal sequence of mountain-denuding fires followed by rainfall 

 of great intensity." 



The slopes above Pickens Canyon, where some of the worst damage 

 occurred, had good shrub and chaparral cover until late in 1933. But late 

 in November, fire destroyed more than 5,000 acres in 3 days. In many places 

 the fire was so hot as not only to wipe out vegetation but also to consume the 

 surface litter. It left only a powdery ash. The ground cooled and lay waiting, 

 utterly defenseless. 



Then rains came. On this Verdugo watershed and on nearby similar 

 watersheds, the Arroyo Seco, San Dimas, and Haines, it started to rain 

 heavily, and with a remarkable uniformity of precipitation, early in the 

 morning of December 30. All that day the rain slashed down, all that night, 

 and all of the day and night following. In the last hour of the "old year" gage 

 records show precipitation reached the peak. Nearly an inch of rain fell in 

 that hour. Total rainfall during the 2-day storm ran between 11% and 12% 

 inches throughout the foothill country just north of Los Angeles. 



On the burned-off watershed, Kraebel estimates, floodwater stripped off 

 and hurled down certainly no less than 50,000 tons of silt, rubble, and 

 boulders from each square mile. The area in question was of about 19 square 

 miles, nearly one-third burned over. 



Nearby, an unburned 17-square-mile forest area, the San Dimas, lost and 

 sent down during the same flood only about one-twentieth as much flood- 

 water, and only about one-tenth of 1 percent as much erosional debris. 



The San Dimas is an experimental forest, equipped to measure run-off 

 under various types of cover and forest management. "Within the forest," 

 Kraebel explains, "are six small watersheds, selected for their likeness in 

 topography and vegetation, and varying in size from 35 to 100 acres. Weirs 



