TECTONIC GEOMORPHOLOGY OF THE WESTERN BLACK MOUNTAINS AND BLACK MOUNTAINS FAULT ZONE, DEATH VALLEY, CALIFORNIA

Morphometric indices are used to describe the tectonic geomorphology of the Black Mountains, Death Valley, California. The Black Mountains are bound by the normal slip Black Mountain fault zone (BMFZ) along its northernmost 60 km with the strike-slip and is divided into 5 sections based on variations in mountain front sinuosity, mountain front/piedmont intersection profile, range crest profile, fault strike, basin concavity index and basin area/fan area. The BMFZ section from Natural Bridge south to Willow Wash is a simple normal fault zone (spatially confined relatively). Similarly, the BMFZ from Desolation Canyon north to Furnace Creek is also a simple normal fault zone that formed during the Quaternary as the BMFZ propagated 6 km north along strike (lengthening). The BMFZ west of Mormon Point is also simple and extended about 2.5 km north along strike during the Quaternary as well. North extension at the Mormon Point salient resulted in basinward stepping of the east-west trending section to the north and uplift of Pleistocene alluvial fan deposits there. Denny explained that the alluvial fans along the BMFZ are small relative to fans on the west side of Death Valley due to the downdropping basin with the alluvial fan area/basin area relations for both piedmonts following power law functions. Willow Wash was an exception to the function with a fan area disproportionally small relative to the basin area. The underfit alluvial fan is explained by the basinward stepping of the east-west trending section north of Mormon Point. Another inconsistency was the disproportionally large alluvial fan at Copper Canyon, which is explained by capture of part of Copper Canyon by Coffin Canyon. Denny did not include in his study the piedmont from Natural Bridge north to Desolation Canyon known as the Artists Drive structural block. Here, the BMFZ consists of a west-dipping normal main fault trace and an east-dipping antithetic normal fault. During the Pleistocene, slip on the antithetic fault uplifted Neogene sedimentary and volcanic rocks defeating streams across the uplifting horst and trapping alluvial fan deposition in the intervening graben. The diffuse BMFZ at Artists Drive has produced fan areas of 6.3-28 km², which are comparable to the alluvial fans on the west, tectonically inactive, side of Death Valley.