The factor of safety of slopes underlain by thick landslides is apparently consistent with laboratory measurements of strength. We back-calculated the stability of the slope that we studied on the downhill side of Delhi Pike, using the same properties as for the thin slides. The computed effective residual friction angles necessary for equilibrium range from 23° for a slope saturated to the ground surface to 12° for a slope with the water level below the failure surface. Both extreme values appear to be unrealistic. We measured saturated conditions to a level of 1 m above the failure surface at the toe and noted the presence of springs locally within the failed mass. On the other hand, near the middle of the landslide, we did not find saturated conditions in the colluvium anywhere above the bedrock; the failure surface in the colluvium was at least 2 m above the bedrock-colluvium contact. Thus, an estimated average residual friction in the range of 16° to 20° would be consistent with field and
laboratory data.