Geomorphic Evidence for Late-Wisconsin and Holocene Tectonic Deformation, Death Valley, California
Eastward tilting of the Death Valley-Panamint Range structural block has resulted in segmentation of alluvial fans in south-central Death Valley. The youngest segment is generally near the fanhead on the east side and always near the toe on the west side. Six episodes of tilting have occurred, three of which postdate the last major high stand of Lake Manly, herein named the Blackwelder stand, which ended about 10,500 yrs ago. Estimates of the volume of sediment deposited after each episode of tilting suggest that distinct tectonic events occurred approximately 200, 1,000, 6,000, 17,000, 30,000, and 42,000 yrs ago. The average tilting rate appears to have increased exponentially with time. On the Black Mountains, immediately east of the structural block, deposits of tufa and of carbonate-cemented lacustrine, alluvial, and colluvial gravel of diverse age are presently perched at elevations up to 100m above present fans in positions where they could not have formed without support from older fans. On the west side of the valley, shorelines cut during the Blackwelder stand are about 30 m lower than these perched tufa and gravel deposits. Calculations based on these observations suggest that the average tilting rate doubled every 23,000 yrs during the late Wisconsin. The present rate is about 0.016 degrees/1,000 yrs.