 An originally fresh to brackish water lake probably persisted through much of the Pleistocene during which coastal California was wetter and cooler than now.Diminished Holocene precipitation and a higher evaporation rate led to shrinkage of the ancestral lake and associated increased salinity which set the stage for clay dune formation.About 30% of the closed or endorheic drainage basin is to the north of the lake and 70% is south of it.