Soil Slips Related to Vegetation, Topography, and Soil in Southern California

Soil slippage, a form of shallow mass soil movement, was studied on the San Dimas Experimental Forest in southern California after several large storms in 1965 and 1966. The three‐part study consisted of analyzing topographic data from 200 random points measured photogrammetrically; measuring soil texture, soil depth, wettability of surface soil, and hydraulic conductivity of slip surface on slipped and stable sites; and mapping and analyzing soil slips to assess the effects of watershed variables. All slips occurred on slopes greater than 80%. The ocurrence of slips was inversely related to the size and density of vegetation. In brush areas, northerly aspects were more stable than southerly ones. Conversion from brush to grass on the experimental forest may have resulted in an additional 135 m 3 /ha of soil slip erosion during the winter of 1965–1966.