Annual sediment yields from small (< 20 sq km) mountain watersheds in the northwestern United States are approximately log normally distributed over time. Stochastic sediment yield models, based on brief, infrequent transport events, reproduce the log normal property. Observed cumulative distributions of annual yields from several Pacific Northwest drainages also appear to be log normal. The property gives a statistical basis for interpreting annual yield data. For example, impacts of watershed disturbance should be assessed by median rather than mean annual yield.