If the bedrock surface is indented, as it is in hollows, groundwater from upslope will flow toward the center of the depression causing higher pore pressures in the axis of the hollow than in the surrounding planar hillslope (Hack and Goodlett 1960; ฆwanston 1967, 1970; Pierson 1977, 1980; Anderson and Burt 1978). Field observations suggest that colluvial wedges mantle spoon-shaped bedrock hollows, and thus have a concave upward longitudinal profile. For example, the hollows studied by Pierson (1977) in the Oregon Coast Range appear to have concave upward profiles and to saturate in their downstream portions during major storms. Humphrey (1982) has developed a finite-element subsurface flow model which predicts that the spoon-shaped geometry will cause the thickness of the perched groundwater to increase rapidly downslope, leading in large rainstorms to saturation of the colluvium at the downslope end of the wedge and, perhaps, to landsliding. Quantification of the geometry of bedrock depressions is thus very important: the stability of the colluvium is largely controlled by concentration of groundwater flow.