El Ni¿o--driven storms triggered widespread slope failures on Santa Cruz Island (SCI), California, during the 1997--1998 winter. After 120 years of intensive grazing, sheep had been removed from the western 90% of SCI in the 1980s. The contrast between sheep-free western SCI and heavily grazed eastern SCI created a natural laboratory for studying the effects of grazing and postgrazing recovery. Logistic regression was used to identify factors that exerted significant control upon slope failure and to test the hypothesis that land use and vegetation were the dominant controls on failure occurrence in 1997--1998. High-resolution air photos were shot immediately before and after the storm season and were precisely orthorectified using a custom-generated 10 m digital elevation model. The before and after orthoimages were used to map 1922 discrete slope failures across the island, of which 720 were measured in the field and 202 were precisely surveyed. Although sheep-grazed land comprised just 10% of the island, 80% of all slope failures occurred in those areas. Additional controls on soil slip occurrence included bedrock lithology, slope aspect, slope curvature, and elevation. The predominate influence of land use on the 1997--1998 slope failures reflects the dramatic vegetative change on SCI in the ~25 years since sheep removal on western SCI. On the basis of the best-fit logistic regression model, slope failures were 67 times less likely with each unit increase in Normalized Difference Vegetation Index. Increases in vegetation density and variety appear to have added significant strength to the soil, reinforcing the surface against widespread slope failures during precipitation events with return times as high as 100 years. Heavy rainfall also occurred in the study area during the 2004--2005 winter, 4 years after removal of the last sheep from all areas of the island in 2001. Field reconnaissance showed that vegetation density had increased markedly, and soil slippage was virtually absent in 2005 in areas heavily impacted in 1997--1998.