The northwest flank of the Ruby–East Humboldt Range is bounded by a 73-km-long normal fault that is composed of three distinct sections, each separated by a 3- to 5-km-wide left step in fault trace. Stratigraphic, structural, and soil relations observed in a trench across the northern section of the fault at Reed Creek indicate the last surface rupture occurred between 4800 and 7600 cal yr B.P., preceded by tens of thousands of years of tectonic quiescence on the fault. Morphologic analyses of single-event scarp profiles suggest that the length of the range front ruptured during a relatively short period of time in the Holocene and allow that the last rupture was synchronous along the entire range front. Offset of a late Pleistocene glacial moraine along the central section of the fault places a maximum bound on the vertical separation rate of the fault at between 0.06 and 0.2 mm/yr.

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