Upper Cretaceous Formations and Faunas of Southern California

Abstract

Rocks of Upper Cretaceous age crop out in three areas in the vicinity of Los Angeles, southern California. The section in the northern Santa Ana Mountains consists of 2,600 feet (more or less) of conglomerates, shales, and sandstones. These are divided into three formations, of which the upper two are further divisible into two members each. The rich faunas from the shales and sandstones are divisible into two major faunal assemblages that have but few species in common. The older assemblage is subdivisible into two minor faunal divisions. The younger assemblage is similarly divisible into three minor faunal divisions. The Cretaceous beds of the Santa Monica Mountains consist of more than 8,000 feet of coarse clastics. These are nearly unfossiliferous with the exception of a 300-foot sandstone bed near the top of the section. This bed contains a fauna that is correlated with the highest faunal subdivision of the Santa Ana Mountains. The Simi Hills Cretaceous consists of more than 6,000 feet of shales and sandstones. Only the lowermost 500 feet plus of this section has yielded fossils. The fossiliferous beds are correlated with the uppermost two minor faunal divisions of the Santa Ana Mountains.