In 1973 Artim and Pinckney proposed two new formations in southwestern San Diego County in strata that was previously thought ·to be part of the Pliocene San Diego Formation. The upper unit which they named the Otay Formation was thought to be comparable to the Miocene Rosarito Beach Formation in northwestern Baja California, Mexico. In the area studied a postive correlation was made between the Otay Formation of San Diego County and the tuffaceous, fine-grained sandstones and siltstones of the Las Glorias and Los Buenos Members of the Rosarito Beach Formation. It is recommended that the Otay Formation be removed from the geologic literature in deference to the formation name, Rosarito Beach Formation, as established in 1970 by John Minch. The Rosarito Beach Formation thins northward from 76 (+) meters in the area mapped just east of Tijuana to zero meters just north of Sweetwater Valley in Southwestern San Diego County, where it pinches out. In the area mapped the horizontal strata of the Rosarito Beach Formation rests disconformably upon the Sweetwater Formation.
