Tectonic geomorphology and soil chronology of the Frazier Mountain area, western Transverse Ranges, California

The western Transverse Ranges is a tectonic and physiographic province characterized by highlands dominated by uplift, erosion and strike-slip faulting and flanked by fold-and-thrust belts. Uplift of the Frazier Mountain originated on thrust faults 2-4 million years before present. These faults and accompanying relic mountain fronts have not been active since the late Pleistocene, and most recent uplift is due to thrust-faulting on the northern and southern flanks of the ranges.;A slip rate of 30-60 mm/yr at Mesa Valley Farm is determined from offset drainage, ;Late-Pleistocene to Holocene stratigraphy is established from soil geomorphic work. The Frazier Mountain soil chronosequence contains four members (Q1-Q4) that range in age from about 1,000 ybp to late Pleistocene.;Evaluation of alluvial fans on the northwestern flank of Frazier Mountain suggest that the fans are segmented. The oldest fan segments are adjacent to the mountain front suggesting that since late Pleistocene time the mountain front has been relatively stable. That is, the rate of uplift at the mountain front has been less than or equal to the rate of downcutting by the streams that drain the mountain.;Regional geomorphic relationship are determined in part by evaluating the Stream-Gradient Index. In general a large part of the central highlands is characterized by relatively low SL indices. However, there are notable exceptions in areas of particular resistant rocks and possible points of stream capture. Areas of relatively high indices are located along the northern and southern fronts of the western Transverse Ranges and are related to active reverse faults. In general, the pattern of the SL indices supports the hypothesis of block uplift of the central part of the Transverse Ranges due to active thrust-faulting on the flanks.;Evaluation of drainage history of the central highlands and particularly Piru Creek suggests a complex history that hypothetically is related to uplift and stream capture. I believe that the complex drainage history is due in part to base level lowering that produced headward entrenchment and migrating knickpoints resulting in significant drainage adjustments.