Stratigraphic evidence suggests that the complex pattern of basins, uplifts, and major faults in southern California has resulted from three successive episodes of late Cenozoic deformation: middle Miocene, Miocene-Pliocene, and Pasadenan.

Surface exposures rimming the southeast Los Angeles basin record a middle Miocene phase of major block faulting on northwest- and north-trending faults; related widespread volcanism implies crustal extension. In late Miocene and earliest Pliocene times, the east-west-trending Transverse Range deformation dominated the northern Los Angeles basin. En echelon, northeasterly sinistral faults may have been the precursors of the east-west Santa Monica fault system, on which 6-8 mi of sinistral Miocene-Pliocene offset has occurred.

Major Pasadenan deformation, involving dextral offset on northwest-trending faults, and reverse faulting on elements of the Transverse Range system, began in late Pliocene time in the Los Angeles region and is continuing. In the Baldwin Hills, continuous deep-water sedimentation into mid-Pleistocene time has recorded several pulses of Pasadenan deformation. Latest Pliocene folding, which developed more than 2,000 ft of structural relief on the Inglewood anticline, was followed by dextral faulting which transected the anticline. Lateral displacement has totaled about 4,000 ft and has been accompanied by formation of an upthrust block on the northeast flank and a graben across the axis. During the past 30,000 years, uplift in this seismically active area has proceeded at 10 times the av rage Pleistocene rate.

In the late Cenozoic deep-water basins of California, detailed stratigraphic studies of deformation history are essential in testing alternative orogenic hypotheses, both in oil exploration and in the evaluation of fault hazards.

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