Recreational use of vehicles, mainly motorcycles, off constructed roads and trails has been heavy in Ballinger Canyon, Los Padres National Forest, California, for the past 8 yr. The vegetation and shallow soils of this arid area have proved sensitive to such use. In the heaviest-use zones, soil and bedrock losses from individual vehicle trails average 600 kg · m−2. Erosion rates in those trails over a period of 8 yr are as high as 250 kg · m−2 · yr−1, and total mass losses from hill-slopes adjacent to the campground average 19,000 t · km−2 · yr−1(t = metric tons). These average annual erosion rates exceed Soil Conservation Service soil-loss tolerances by a factor of 86 and exceed the already very high natural denudation rate of the Transverse Ranges by a factor greater than 5.