Prior to the late 1960s almost all prehistoric cultural remains known in the northern end of the Sacramento Valley and surrounding mountains were assigned to a single cultural complex and dated within the past 1,000 years. A considerable accumulation of archaeological data within the past 25 years has led to an extensive elaboration of regional prehistory which is divided into 5 temporally and/or spatially discrete patterns spanning the past 8,000 years. This paper, one of a group of regional summaries presented on the occasion of the 25th anniversary of the Society for California Archaeology, reviews archaeological investigations and describes the cultural patterns and chronology as they are presently interpreted.