A paleogeographic reconstruction of southeastern California and southwestern Arizona at 10 Ma has been made based on available geologic and geophysical data. Clockwise rotation of 39¿ has been reconstructed in the eastern Transverse Ranges, consistent with paleomagnetic data from late Miocene volcanic rocks, and with slip estimates for left-lateral faults within the eastern Transverse Ranges and NW-trending right-lateral faults in the Mojave Desert. This domain of rotated rocks is bounded by the Pinto Mountain fault on the north. The model requires that the western part of the late Miocene Pinto Mountain fault was a thrust fault, which gained displacement to the west, because of the absence of evidence for rotation of the San Bernardino Mountains or for significant right slip faults within the San Bernardino Mountains. The Squaw Peak thrust system of Meisling and Weldon (1989) may be a western continuation of this fault system. The Sheep Hole fault bounds the rotating domain on the east. East of this fault an array of NW-trending right slip faults and south-trending extensional transfer zones has produced a basin and range physiography while accumulating up to 16 km of right slip.

This maximum is significantly less than the 37.5 km of right slip required in this region by a recent reconstruction of the central Mojave Desert (Dokka and Travis, 1990a). Geologic relations along the southern boundary of the rotating domain are poorly known, but this boundary is interpreted to involve a series of curved strike slip faults and linking normal faults that accommodated noncoaxial extension. Quaternary movement on the Pinto Mountain and nearby faults is unrelated to the rotation of the eastern Transverse Ranges, and a hiatus during part of the Pliocene time followed the deformation which produced the rotation. The reconstructed Clements Well fault in the Orocopia Mountains, proposed as a major early Miocene strand of the San Andreas fault, projects eastward towards Arizona, where early Miocene rocks and structures are continuous across its trace, making large displacements on this structure unlikely. The model predicts a 14¿ clockwise rotation and 32% extension during late Miocene and early Pliocene time along a NW-trending line parallel to the present trace of the San Andreas fault. Palinspastic reconstructions of the San Andreas system based on this proposed reconstruction may be significantly modified from current models. ¿ American Geophysical Union 1993