PRELIMINARY DIGITAL GEOLOGIC MAP OF THE LOS ANGELES 30' X 60' QUADRANGLE, SOUTHERN CALIFORNIA

The Los Angeles 30’ x 60’ quadrangle covers nearly 5,000 km2 including some of the most densely populated urban and suburban areas of southern California. It extends 90 km E-W and 55 km N-S, from Fillmore and Thousand Oaks in the west to Vincent in the northeast and Montebello in the southeast. Urban and suburban areas include the San Gabriel Valley and San Gabriel Mountain foothill west of Monrovia, Pasadena, Glendale, downtown Los Angeles, Hollywood, Santa Monica, Malibu, and all the communities in the San Fernando Valley, Simi Valley, and the upper Santa Clara River Valley. The population of these areas totals approximately 5.6 million, and estimates of property value total hundreds of $billions. Residents and transient visitors are subject to potential hazards from earthquakes, debris flows and other landslides, floods, wildfires, subsidence from ground water and petroleum withdrawal, and swelling soils; and coastal areas are exposed to flooding and erosion by storm and tsunami waves.

The quadrangle includes significant areas of wilderness in the Angeles and Los Padres National Forests, the Santa Monica Mountains National Recreation Area, and the Sespe Condor Sanctuary. Relief ranges from a few hundred meters sub sea in Santa Monica Bay to more than 2,000 meters above sea level at Pacifico Mountain in the high San Gabriel Mountains. The map shows the general distribution of the rocks and engineering soils of the area and their structural and stratigraphic relations to one another, and provides a regional geologic framework to aid evaluations of the potential for hazard from active earth processes. It is a synthesis of the work of many scientific studies by many workers. We have not attempted to resolve many problems of stratigraphic correlation and nomenclature; in most cases, the unit designations of source-map authors have been retained. We hope that the map will stimulate further work to describe and correlate the many units into a more coherent, more accurate geologic history.