CHAPARRAL COVER, RUN-OFF, AND EROSION 



807 



The chaparral cover on sandstone areas was decidedly scanty and 

 composed chiefly of tarweed, sage, and chamise \\ith a density of .3 

 and a protective value from an erosion and water standpoint of .2 

 on a scale of 1.0. Tlie granitic soils supported a much better stand 

 of chaparral with a mixture of the brush species, the composition and 

 density of the stand depending upon the depth of the soil, degree of 

 slope, elevation, exposure, and physiographic location. Erosion was 

 slight and confined to areas where the soil mantle was shallow, as on 

 steep slopes or on isolated areas where landslides had occurred. There 

 was a heavy brush cover in the Dalton and San Dimas Canyons, rather 

 uniform as to height and density, and \ery few places where much rock 

 outcropped to any extent. The early examinations of the area dis- 

 closed no evidence of erosion from the sidehills, which would certainly 

 have shown up in the heavy storms of 1914 and 191 G, though there 

 was considerable erosion of the stream bed itself, due to the high 

 velocity and volume of the water during the floods. 



The condition of these drainage basins with their areas is shown 

 below, together with the other drainage basins in which the fires burned 

 in 1919. 



CONDITION AFTER THE FIRE, OCTOBER, 1919 



The area burned over by the two fires was first examined in October, 

 about a month after the destruction of the cover. At this time the 

 amount of vegetation not destroyed in the path of the fire in these 

 areas was limited to much less than one per cent of the total, and 

 found in isolated spots on the sidehills where the fire had jumped, or 

 in the bottom of the drainage basins where the fire burned more 

 slowly or where natural barriers interfered with its progress to such 



