TECTONIC GEOMORPHOLOGY, STREAM CAPTURE AND ALLUVIAL FAN/BASIN AREA RELATIONS ALONG THE BLACK MOUNTAINS, DEATH VALLEY, CALIFORNIA

The Death Valley half graben in the southwestern Basin and Range of California has long been a focal point of tectonic geomorphology especially with respect to alluvial fans, drainage basin and fault zone interactions. Pioneering work here established the logarithmic relations between basin area and fan area along with the observation that smaller alluvial fans and basins form along the active fault whereas larger fans and basins are found on the passive side of the basin. The Black Mountain fault zone (BMFZ), the active normal fault on the east side of Death Valley, is divided into five segments based on variations in mountain front sinuosity, mountain front/piedmont intersection profile, range crest profile, fault zone strike, basin area and basin concavity index. Much of the previous work on alluvial fan/basin relations has focused on a single-strand, uncomplicated segment of the BMFZ segment that produces a linear relationship between basin area and fan area. The basin/fan area relation is more complicated when the entire BMFZ is considered. At Mormon Point, an en-echelon step in the BMFZ is related to northward propagation of one segment, basinward stepping of another and abandonment of a third. This results in a smaller fan area relative to the adjoining basin. Another smaller fan/larger basin relation is found at Coffin Canyon, which has captured part Copper Canyon. At Artists Drive, the west-dipping normal fault includes an east-dipping antithetic fault that developed in the late Pliocene. This resulted in alluvial fan deposition in a graben near the mountain front, capture, and larger alluvial fans compared to the basin size. As has been noted by several studies, the final alluvial fan/basin are disequilibrium is the man-made capture of the Furnace Creek basin into Gower Gulch. This has resulted in increased scour within the basin due to the ~66 m base level drop and initiation of the enlargement of the Gower Gulch alluvial fan. Outside of anthropogenic drivers, anomalies noted in the original fan/basin area studies are explainable within the framework of subsequent studies in basin and range geomorphology related to changes in the BMFZ.