Holocene and Latest Pleistocene Oblique Dextral Faulting on the Southern Inyo Mountains Fault, Owens Lake Basin, California

Abstract

The Inyo Mountains fault (imf) is a more or less continuous range-front fault system, with discontinuous late Quaternary activity, at the western base of the Inyo Mountains in Owens Valley, California. The southern section of the imf trends ∼N20°–40° W for at least 12 km at the base of and within the range front near Keeler in Owens Lake basin. The southern imf cuts across a relict early Pliocene alluvial fan complex, which has formed shutter ridges and northeast-facing scarps, and which has dextrally offset, well-developed drainages indicating long-term activity. Numerous fault scarps along the mapped trace are northeast-facing, mountain-side down, and developed in both bedrock and younger alluvium, indicating latest Quaternary activity. Latest Quaternary multiple- and single-event scarps that cut alluvium range in height from 0.5 to 3.0 m. The penultimate event on the southern imf is bracketed between 13,310 and 10,590 cal years b.p., based on radiocarbon dates from faulted alluvium and fissure-fill stratigraphy exposed in a natural wash cut. Evidence of the most recent event is found at many sites along the mapped fault, and, in particular, is seen in an ∼0.5-m northeast-facing scarp and several right-stepping en echelon ∼0.5-m-deep depressions that pond fine sediment on a younger than 13,310 cal years b.p. alluvial fan. A channel that crosses transverse to this scarp is dextrally offset 2.3 ± 0.8 m, providing a poorly constrained oblique slip rate of 0.1–0.3 m/k.y. The identified tectonic geomorphology and sense of displacement demonstrate that the southern imf accommodates predominately dextral slip and should be integrated into kinematic fault models of strain distribution in Owens Valley.