IN SEARCH OF TECTONIC BOUNDARY STRUCTURES THAT ACCOMMODATED LARGE VERTICAL-AXIS ROTATION OF THE WESTERN TRANSVERSE RANGES IN SOUTHERN CALIFORNIA

New paleomagnetic, stratigraphic, and structural data were used to determine the structural framework and fault kinematics that allowed the western Transverse Ranges to rotate more than 90 degrees during Late-Cenozoic time. This study was conducted along the north edge of the rotated region where the western Transverse Ranges abut non-rotated crust to the north. Paleomagnetic declinations and Late-Tertiary depositional environments contrast sharply across the west-striking western Big Pine- Pine Mountain fault indicating that this fault defines the north boundary of the rotated terrain. The western Big Pine- Pine Mountain fault dips to the north from 45 to 80 degrees and exhibits primarily dip-slip displacement which increases westward away from the pole of rotation for the western Transverse Ranges block. This fault has accommodated approximately 60 to 70 degrees of rotation, whereas the remaining amount was distributed across a westward–opening zone of smaller reverse faults and folds south of the major boundary fault. These new observations help refine previous models of vertical-axis rotation in southern California, and provide previously lacking geologic and structural data needed along the northern edge of the western Transverse Ranges to document rotation.