In the Rosarito Beach area, tilted Early Cretaceous metavolcanic rocks of the Alisitos Formation are overlain with angular unconformity by essentially flat-lying mudstones and sandstones of the Rosario Formation. Faunal analysis indicutes that the Rosario Formation is of Upper Cretaceous age (Campanian to Early Maestrlchtin) and was deposited in a cold, deepwater marine environment. Disconformity separates the Rosario Formation from Later Cretaceous-Early Tertiary conglomerate of Formatlon A. A paleosol developed on Formatjon A is overlain by Eocene(?) sandstone and conglomerate of Formation B. A series of interbedded Tertiary basalts and sandstones overlie Formatlon Band arc :tn turn unconformably overlain by Pleistocene terrace deposits.