Southern California and the northern part of the peninsula of Baja California form a common region affected by a number of regional-scale active faults, all constituting part of the San Andreas-Gulf of California fault system. The Cerro Prieto-Imperial fault is located in the Mexicali-Imperial Valley, and the Cucapa and the Laguna Salada faults constitute the southern extension of the Elsinore fault. South of the Laguna Salada are two lineaments, the El Chinero and the San Felipe. The second extends southward, connecting with an extensional region near Puertecitos. West of the two lineaments, the San Pedro Martir fault and the Sierra de Juarez fault constitute part of the Main Gulf Escarpment. In the peninsula of Baja California, two main active fault systems are recogniz d--the Agua Blanca fault, which is oriented anomalously counterclockwise to the general trends of the southern San Andreas fault system, and the San Miguel-Vallecitos faults, which extend from the Sierra de Juarez escarpment toward the Tijuana-San Diego

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area. Both the Agua Blanca and San Miguel-Vallecitos faults extend offshore and connect with active faults in the Continental Borderland.

All these faults are seismically active to different degrees as a result of the interaction between the Pacific-North American plates in the Gulf of California region. Although in the northern Gulf the amount of displacement measured between plates is less than in the southern Gulf, the difference in movement (2.5 to 3.0 cm/yr) can be spread along the strike-slip faults on the peninsula and those on the Continental Borderland. A structural relationship should exist between the Guaymas lineament and the Puertecitos extensional region, which is the conduit where movement is induced to the onshore peninsular faults.