Land use around the larger cities in California has changed as agriculture has given way to urbanization. From 1950 to 1970 this change was especially rapid in the Berkeley hills, which lie to the east of San Francisco Bay. Streamflow characteristics in the hills have changed significantly as a result. Since knowledge of these changes is important for responsible water planning and aquatic wildlife management, this report summarizes the results of a preliminary study of the impact of urbanization on periodicity of streamflow.