EOCENE ORIGIN OF OWENS VALLEY, CALIFORNIA

Bedrock apatite and zircon (U-Th)/He data reveal an Eocene exhumation difference greater than four kilometers athwart Owens Valley, California near the Alabama Hills. This difference is localized at the eastern fault-bound edge of the valley between the Owens Valley Fault and the Inyo-White Mountains Fault. Time-temperature modeling of published data reveal a major phase of tectonic activity circa 54 Ma of a magnitude equivalent to the total modern bedrock relief of Owens Valley. Exhumation of the Inyo Mountains in early Eocene time at a rate of circa 1000 m/m.y. was contemporaneous with exhumation of the high Sierra Nevada immediately to the west at a much lower rate, roughly 50 m/m.y. in the vicinity of Mt Whitney. This difference was most likely accommodated by one or both of the Owens Valley and Inyo-White Mountains fault zones, requiring an Eocene structural origin of Owens Valley, 40 million years earlier than previously estimated.