LATE MIOCENE PLEISTOCENE EXTENSIONAL FAULTING, NORTHERN GULF OF CALIFORNIA, MEXICO AND SALTON TROUGH, CALIFORNIA

A belt of low-angle normal (or detachment) faults similar to 250 km lo ng extends from the northern end of the Salton Trough, California to s outhern Laguna Salada, Baja California, Mexico. The detachment system is divided into two principal segments. The northern segment, here ter med the ''west Salton detachment system,'' comprises top-to-the-east d etachment faults along the eastern Peninsular Ranges that root under t he Salton Trough. The southern segment, here termed the Laguna Salada detachment system, comprises top-to-the-west detachment faults in nort heastern Baja California and the Yuha Desert region of the southwester nmost Salton Trough. Detachments of that system root under Laguna Sala da and the Peninsular Ranges of northern Baja California. Both of thes e systems experienced a major episode of activity in late Miocene to P leistocene time, synchronous with deposition of the Imperial and Palm Spring formations, and the Laguna Salada detachment system may still b e active. Thus, their activity temporally overlapped, partly or comple tely, with activity on dextral faults of the San Andreas boundary betw een the Pacific and North American plates, and with accretion of new t ransitional crust. Some of the detachment faults in the northern segme nt may have had mid-Miocene normal slip and/or Cretaceous thrust or no rmal slip as well, although compelling evidence for either is lacking. These detachment faults are distinctly younger than detachments east of the San Andreas fault, which generally ceased activity by middle or late Miocene time and are overlapped by marine or lacustrine rocks (B ouse Formation); these units are equivalent in age to the syntectonic strata of the Salton Trough but are much thinner and essentially undef ormed.