Redefinition of Cenozoic Stratigraphic Column in Split Mountain Gorge, Imperial Valley, California: GEOLOGIC NOTES

Abstract

This paper proposes some modifications of the stratigraphic terminology as it presently is applied throughout the southwestern Imperial Valley. The Split Mountain Formation is redefined and its stratigraphic limits restricted to include beds critical to its recognition in the original typological sense. Lithologically distinctive lower strata are defined formally as a new stratigraphic unit, the Anza Formation. The Alverson Andesite has been assigned anomalous positions within the stratigraphic column, either above or below the Split Mountain Formation. The formation predates the Split Mountain Formation and is in part a volcanic lithofacies of the Anza Formation. Andesite boulders are a minor component of conglomerate lenses within the upper Anza Formation. No change in efinition of the younger Neogene formations is necessary. Biostratigraphic evidence indicates that the Imperial Formation is of Pliocene age, and that the overlying Palm Spring Formation accumulated throughout late Pliocene to middle Pleistocene time. Marine connection between the Imperial Valley and the Gulf of California was maintained intermittently until the middle Pleistocene.