Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region

Four of the mountain ranges near Death Valley, California, display exhumed, low-angle normal faults on their flanks, features originally referred to a s turtleback structures. These fault surfaces are smooth, planar to curvipl anar, and defined by faceted spurs and coincident interfluve crests. The lo west parts of these faults are overlain in tectonic contact by poorly indur ated fanglomerate, and locally by Quatenary volcanic rocks. Steep fault sca rps in alluvium are present at the foot of each turtleback-type flank. Although these may be examples of active low-angle normal faults, it is dif ficult to establish the dip histories of these faults. The problem with con straining the dip histories is one of missing and concealed information, be cause the exposed hanging-wall rocks are some of the youngest material cut and displaced by the (currently) shallow-dipping faults. Another important relationship along these range flanks is the intersection between the low-a ngle faults and steep, scarp-forming faults that cut alluvium at the range fronts. Although this relationship remains unconstrained ill most of the ra nges, a shallow-dipping fault is cut by one of the steep faults in Panamint Valley, suggesting that, in one area at least, the low-angle faults are no t active. The low-angle faults, and not the steep neotectonic faults, are probably re sponsible for most of the opening of the present valleys, because each low- angle fault intersects the valley floor at the range front. None of the low -angle faults are perched high in the ranges, as would be the case if the s teep Faults had uplifted them significantly. Therefore, even if there has b een a geologically recent transition from low-angle normal faulting to stee p normal (with or without strike slip) faulting, the modern topography stil l reflects the former regime. Strictly speaking, the Death Valley region ma y not be an example of active low-angle normal faults and supra-detachment basins.