ORIGIN OF THE POVERTY HILLS, OWENS VALLEY, CALIFORNIA, AND IMPLICATIONS FOR THE TECTONIC EVOLUTION OF THE OWENS VALLEY BASIN

The Eastern California Shear Zone (ECSZ) between the Sierra Nevada and the Great Basin is a transtensional zone of right-lateral distributed shear along NW-oriented strike-slip faults. This zone of active deformation defines an oblique rift zone behind the NW-moving Sierra microplate. In the southern ECSZ, this translation is accommodated by en-echelon faults including the dextral Owens Valley Fault (OVF). The Poverty Hills (PH), an isolated structure located at a left stepover along OVF, consists of basement rocks in tectonic contact with Quaternary volcanic rocks of the Big Pine volcanic field.

Structural field data indicate a complex tectonic origin for the Poverty Hills. The NW-trending elliptical body of PH is composed of deformed granodiorite in the eastern and fossiliferous Paleozoic sandstone-siltstone with a White-Inyo Mountains origin in the western half. The granodiorite is intrusive into the metasedimentary rocks that are folded around NW-trending fold axes. Pyroclastic rocks and lava flows produced by isolated volcanic eruptive centers within PH are tectonically intercalated with the basement rocks both in the east and the SW. NW-striking, NE-directed en-echelon reverse faults form duplexes within the granodiorite in the east. These structures collectively represent a positive flower structure in a transpressive regime at a left stepover along OVF. At the NW edge of PH occurs a N-S running oblique normal fault zone with top-to-the west sense of movement, uplifting basement rocks and the Quaternary fluvial deposits of the Tinemaha Creek in the footwall. This fault zone represents a local transtensional regime around the NW edge of PH. We interpret PH as a tectonic fault block that was isolated from the White-Inyo Mountains during the extensional evolution of the Owens Valley graben. Establishment of OVF within this graben system as part of ECSZ in the late Quaternary caused the uplift of PH and deformation of the lava flows. These structural relations provide important chronological and kinematic constraints for the tectonic evolution of the Owens Valley and ECSZ.