The impact of military training activities (primarily foot traffic) on soils and vegetation was assessed at the United States Air Force Academy, Colorado, USA. In May-June 1998 after 2 years of intensive training use, mean bulk densities of the top 6 cm of soil in the high-use site (1.37 g/cm(3)) and moderate-use site (1.30 g/cm(3)) were significantly different from bulk density of the reference site (1.04 g/cm(3)). Mean infiltration rates on the high use site (0.63 cm/min) and moderate use site (0.67 cm/min) were significantly different from the infiltration rate on the reference site (3.83 cm/min). Soil water holding capacities of the three sites were not significantly different. Descriptive comparisons of total aboveground biomass and litter indicated a 68% decrease in total aboveground biomass and a 91% decrease in litter when the high-use site was compared to the reference site. Using the Universal Soil Loss Equation, an estimated soil erosion rate for the reference plot (0.07 tons/ha/yr) was 30 times less than the erosion rate for the high use plot in the center of the basic cadet training encampment area (2 tons/ha/yr) and between 7 and 6 times less than the moderate use plot and the high use plot on the edge of the encampment area (0.5 and 0.4 tons/ha/yr, respectively). Therefore, training use appears to adversely affect bulk density, infiltration, total aboveground biomass, litter, and erosion. Without implementation of restoration practices, further site degradation is likely.