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Orbital photographs of the Peninsular Range province of southern California and Baja California have been studied to test the concept that the Agua Bianca and Elsinore faults are transform faults, with major right-lateral displacement (Fig. 1). Field checking has been limited to short reconnaissance trips.

The Agua Bianca fault, as it appears on Gemini and Apollo photographs, is but one of several parallel faults. On the north, one of these faults—the Portrerillo fault—evidently cuts an igneous intrusion without lateral displacement. The Agua Bianca fault itself cuts several sizable canyons without visible lateral displacement. It does not extend past the east front of the Sierra de Juárez and the Sierra de San Pedro Mártir to the Gulf of California, as required by the transform-fault concept, nor is there evidence of a terminating rift northeast of Ensenada. This cumulative evidence, which requires further field checking, suggests that movement on the Agua Bianca fault has been chiefly localized dip slip and that there has not been substantial lateral movement along the fault as a whole. Field evidence for right-lateral displacement, reported by Allen et al. (1960), is probably the result of relatively recent, localized movement.

The Elsinore fault has been examined on Apollo 9 photographs and locally in the field between Lake Elsinore and the Tierra Blanca Mountains. Several previously unmapped north-east-trending fractures appear to cross the Elsionre fault without lateral displacement. The Elsinore fault does not displace the Sawtooth Range, which also crosses its trace, and there is

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