This study quantified the vertical distributions of 294 taxa of phytoplankton from 112 samples in a vertical section across the California Current system off Southern California. The goal was to examine the relationship between coastal and offshore floras throughout the euphotic zone. The two associations were distinct throughout the upper 140 m. The coastal flora was found in water adjacent to and east of the Santa Rosa Ridge. The offshore flora occurred west of the California Current, and also at the station immediately east of the current, presumably the result of upstream entrainment across it. Both coastal and offshore floras were similar to the analogous floras described from the mixed layers in the springs of 1993 and 1995, in spite of different ENSO conditions prevailing during the three years.There were two unexpected results. Although the hydrographic characteristics of offshore water had been strongly modified by mixing with California Current water, the offshore flora remained similar to that of a central Pacific study site, 3000 km to the west. Clearly, the maintenance of this species association is not directly dependent upon temperature or salinity. In contrast, even though the temperature-salinity relationship of the California Current fell within the envelop of T-S relationships of source water to the north, the floristic analyses identified no flora unique to the California Current. Absence of oceanic subarctic species in the Current may be related to upstream depletion of nutrients.