Water resources data for the 1991 water year for California consist of records of stage, discharge, and water quality of streams; stage and contents in lakes and reservoirs; and water levels and water quality in wells. Volume 1 contains dischrage records for 171 streamflow-gaging stations, 16 crest-stage partial-record streamflow stations, and 3 miscellaneous measurement stations; stage and contents records for 24 lakes and reservoirs; water-quality records for 23 streamflow-gaging stations, 4 partial-record stations; and precipitation records for 16 stations. These data represent that part of the National Water Data System operated by the U,S. Geological Survey and cooperating State and Federal agencies in California.