CHAPARRAL COVER, RUN-OFF, AND EROSION 809 



indications were that some would form with further rains. In the 

 sandstone region there was not a great deal of erosion, probably 

 because of the heavier soil particles, the absorption of water, or the 

 presence of a binding agent. Little erosion took place in the stream 

 beds ; for the streams did not respond markedly to this precipitation 

 because the ground was exceedingly dry and absorbed a large part 

 of the water. Where the water did attain a velocity of any conse- 

 quence, the stream bed eroded to some slight extent. 



Prior to the fire 238 small "check dams" had been built by the 

 County Flood Control Engineer in the Little Dalton Canyon, which 

 has an area of 3.2 square miles. After the first storms it was found 

 that five per cent of these were completely filled in by deposits from 

 small drainage areas above them, and an additional six per cent were 

 partially filled from this same cause. It was estimated that behind all 

 the dams there was in the neighborhood of some 600 cubic yards of 

 material, and that altogether in this drainage basin 2,500 cubic yards 

 of material had been moved from the sidehill into the stream beds 

 or small draws whence the winter rains would carry the material into 

 the main stream. In one small side canyon 26 of these small dams 

 were constructed. The lower end of this basin had not been burned 

 over and twelve check dams were situated in that part of the area 

 where the fire had occurred. Of these, five were completely filled by 

 the first storm, three were three-fourths filled, and four more were 

 partially filled, containing material up to one-half the capacity of 

 the dams. At the end of the winter season the deposits had completely 

 filled up twelve dams and there was more or less lighter material, such 

 as leaf mold and litter, in the storage basins behind the dams. A 

 storm of rather high intensity visited the region on the night of March 

 1, when the ground was fairly well saturated with moisture, with the 

 result that all but one dam was completely silted in and this one con- 

 tained considerable fine material which sealed all the crevices in the 

 dam and formed a large pool. 



It was estimated in the early winter that the number of chaparral 

 stems which would not sprout would amount to some 40 per cent, 

 but examination of a number of plots laid out on different slopes and 

 aspects shows that only 3.5 per cent of the brush cover is not sprout- 

 ing, and it is believed that this will still further be reduced by some 

 of the stumps sending out sprouts later on in the season. In deep 

 soil on gentle slopes where erosion had not been severe there was a 



