We investigated short-term effects of ski-run development on the dynamics of small mammal populations at Vail Ski Area, Colorado. We compared a new ski run, an experimental ski run with added woody debris, a forest adjacent to a new ski run, and a control forest outside ski development by estimating density and survival of common small mammals using Pollock's robust design. In 4 summers (1998–2001), 16,800 trap nights resulted in 1,276 captures of 668 individuals. Before ski-run development, Clethrionomys gapperi was most abundant in forested areas, but after, density was greatest in the forested site adjacent to a new ski run and next highest on the experimental ski run. C. gapperi survival was similar across sites and years. Peromyscus maniculatus and Tamias minimus densities were greatest on the ski run without woody debris and lowest on the forested control site. Estimated survival of T. minimus varied more by year than by site. Greatest densities of Phenacomys intermedius occurred on the 2 ski runs in years following development, and densities were low on forested sites. Peromyscus maniculatus and Phenacomys intermedius captures were insufficient to estimate survival. Our results suggest that C. gapperi, in the short term, will inhabit ski runs with tree islands and woody debris. Additional studies on impacts of ski-run development are needed to understand small mammal responses and to promote effective management strategies for maintaining populations of forest-dwelling animals.