Abstract

The Poverty Hills are a 5 km2, 300-m-high mass of plutonic and meta-sedimentary rocks exposed along the axis of the alluviated Owens Valley graben in eastern California. Two models have been proposed for the origin of the hills. One model suggests the hills represent a transpressional uplift along a 3-km left-step in the right-lateral Owens Valley fault zone, and the other proposes that the hills are a long-runout rock-avalanche deposit. This article argues that the rock-avalanche hypothesis best fits the geology. The transpressional model is problematic because the fault segment to which right-lateral displacement is purportedly transferred has been shown to have pure dip-slip displacement. The rock-avalanche model is based primarily on lithologic evidence. Throughout the hills are scattered outcrops displaying mosaic, jigsaw, and crackle breccia textures, all of which are characteristic of rock-avalanche deposits. Also, well-exposed roadcut outcrops display preserved source-rock bedding within the matrix-poor breccia framework. Though preserved, the bedding has been contorted and distorted by cataclastic flow of the breccia, another common characteristic of rock-avalanche deposits created during emplacement. The landslide is younger than 3 Ma, the age of inception of the Owens Valley graben, and older than 640 ± 50 ka, the age of a basalt flow that post-dates the landslide. An area in the Inyo Mountains southeast of the hills appears to be the most likely source. Interpretation of the Poverty Hills as a landslide mass suggests an alternative model for the Owens Valley fault-zone kinematics.

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