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Brief Report for Black Mountains fault zone, Mustard Hills transition zone (Class A) No. 142a

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Compiled in cooperation with the California Geological Survey

citation for this record: Machette, M.N., Klinger, R.E., and Piety, L.A., compilers, 2001, Fault number 142a, Black Mountains fault zone, Mustard Hills transition zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website,, accessed 04/18/2014 12:59 PM.

Synopsis General: The Black Mountains fault zone is marked by prominent Holocene and late Pleistocene scarps that are more-or-less coincident with strongly uplifted western margin of the Black Mountains in central Death Valley and their northward continuation as low hills cored by upper Tertiary sedimentary rocks. The fault zone is part of the much longer Death Valley fault system, which extends from Fish Lake Valley (Nevada) in the north, to the Garlock fault [69] in the south. The Black Mountains fault zone is characterized by primarily normal to normal-oblique along its length, and its footwall block is a spectacular example of active tectonic uplift. The fault zone is somewhat irregular in map plan, strikes roughly north-south (on average). It joins the northwest-striking Northern Death Valley fault zone [141] and the predominately pre-Quaternary Furnace Creek fault zone on the north, and the northwest-striking Southern Death Valley fault zone [143] on the south to form a nearly continuous 300-km-long feature that is one of the most active fault systems in the region. Detailed studies of offset alluvial fans along the Black Mountains suggest normal-dip slip rates of 1-3 mm/yr as recorded by near vertical scarps as much as 10 m high on Holocene alluvium at Willow Wash, east of Mormon Point. Recurrent Holocene movement characterizes the entire fault zone, and some portions may have been active as recently as 200 years ago. Continuous scarps associated with the Black Mountains fault range from 2 to 13 km in length, and although the majority of the range front is fault controlled, active sedimentation has obscured some traces of the fault. Although no trenching studies have been conducted on the fault zone, the entire trace is well mapped, and morphometric studies suggest potentially different times of movement along the fault zone and amount of offsets in a variety of Holocene to late Pleistocene deposits.

Sections: This fault has 4 sections. In general, the Black Mountains fault zone strikes shows little evidence for major steps or potential section or segment boundaries (Machette and others, 2001 #4773). The exceptions are a large embayment in the range north of Mormon Point (Mormon Point Turtleback), a 12-13 km-long gap in terms of scarp continuity north of Natural Bridge (Klinger and Piety, 1996 #3873), and the lack of fault continuity north of Furnace Creek). Very little substantial paleoseismic work has been done to support potential subdivision of this roughly 70-km long fault zone. Various schemes have been proposed, the most recent being two sections for the south half of the fault based on scarp morphometric data (Frankel and others, 2001 #4776), six sections based on topical studies by Knott and others (2001 #4772), and eleven sections based on geometric considerations (Brogan and others, 1991 #298). Knott (1998 #5116) subdivided the range front into six distinct geometric segments based on variations in the mountain front sinuosity, mountain front-piedmont intersection profiles, range crest profile, the strike of the fault, and several other factors. For purposes of estimating the potential magnitude of future earthquakes on the Black Mountains fault zone, Knott (1998 #5116) recombined his six segments into three longer segments with lengths similar to the shorter historical ground ruptures reported by Wells and Coppersmith (1994 #546). The most distinct geomorphic boundaries (or anomalies) along the range, Mormon Point and Natural Bridge, separate each of these three longer segments. This is consistent with a 3-part segmentation scheme of the range-front fault based solely on scarp morphology (Klinger and Piety, 1996 #3873)). For this database, we divided the Black Mountains fault zone into three subequal length sections and include the transition zone (modified from Machette and others, 2001 #4773). This subdivision is based primarily on fault trend, structural features (bedrock salients and asperities), fault continuity, location of the fault relative to the range, and apparent recency of movement. From north to south, these are defined as the 1) Mustard Hills transition zone, 2) Artists Drive section, 3) Copper Canyon section, and 4) Smith Mountain section. Each of these are named for prominent geographic features with the section
County(s) and State(s) INYO COUNTY, CALIFORNIA
Physiographic province(s) BASIN AND RANGE
Length (km) This section is 8 km of a total fault length of 70 km.
Average strike N34°W (for section) versus N17°W (for whole fault)
Sense of movement Normal
Dip Direction W; SW; NE
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)
Slip-rate category Less than 0.2 mm/yr
Date and Compiler(s) 2001
Michael N. Machette, U.S. Geological Survey
Ralph E. Klinger, U.S. Bureau of Reclamation
Lucy A. Piety, U.S. Bureau of Reclamation