Map showing recently active breaks along the Hayward fault zone and the southern part of the Calaveras fault zone, California

This map is one of a set that shows the traces of the inferred most recently active faults of the San Andreas and related fault zones of the San Andreas fault systems (Cromwell, 1962.) It was compiled primarily to provide information for those concerned with land use and development on or near these fault zones. The map shows the locations of all known or suspected fault traces formed by recent tectonic displacements of the ground surface along the Hayward and the southern part of the Calaveras fault zones. The displacements may have been due to violent rupture during earthquakes, to imperceptible movement not accompanied by felt earthquakes (slippage or "creep"), or to some combination of both. Map users should keep in mind that the lines shown on the map are primarily guides for locating fault traces on the ground and are not necessarily located with the precision needed for every engineering or land-use project.