During the summer, material normally slides from slopes into slope channels and areas of low relief when soil moisture and cohesion is low. During the winter, fluvial erosion scours the debris from the channels. In recent years, the amount of material moved into intermontane areas during the summer months far exceeds the amount removed from these areas during the winters. The high drainage density and lack of substantial intermontane deposits of alluvium and colluvium indicate the operation of a process other than normal erosion. A study of erosion following a fire in the San Dimas Forest shows that the fire-flood sequence has, in a short time, removed the products of 40 years of normal erosion.