Future climatic changes associated with the enhanced greenhouse effect are expected to bring about an intensification of the hydrologic cycle and subsequent changes in extreme weather events. Several past studies have focused on the evidence for such changes in observational records at local to continental scales. Such research often involves relatively short records, small trends, and large natural variability. In this presentation, we focus on the climatology of “extreme” precipitation and streamflow in Southern California based on the 57-year period from 1948 through 2004. The region extends from the northern county lines of San Luis Obispo, Kern, and San Bernardino counties southward to the Mexican border. The region is characterized by a strong seasonal cycle in precipitation and streamflow along with high sensitivity to climatic oscillations such as ENSO. For this analysis, a total of 132 daily precipitation station records and 84 hourly precipitation stations records were used. For the analysis of streamflow, we focused primarily on the cismontane region extending from the Transverse and Peninsular Mountain Ranges to the Pacific Ocean. Heavy or “extreme” precipitation and streamflow are defined based on the frequency distributions at each station (for example the upper 25% or 15% precipitation or streamflow with given return period). In addition to the characterization of the regional climatology of precipitation and streamflow, we examine the occurrence of heavy precipitation and high streamflow and present attributes of this occurrence over the 57-year period of analysis and for the study region.