STRUCTURAL NATURE OF A LARGE DISCONTINUITY IN THE SIERRA NEVADA EXTENSIONAL FAULT SYSTEM: THE COYOTE "WARP" OF NORTHERN OWENS VALLEY, CALIFORNIA

The Sierra Nevada escarpment adjacent to Owens Valley, California, forms part of the western edge of the southern Basin and Range province. High rates of recent extensional and right-lateral faulting characterize this region, focusing much attention on understanding the complex distribution of deformation in Owens Valley. Here we discuss a major discontinuity in the Sierra Range range-front known as the Coyote Warp, a sloping topographic feature at a large stepover between the Sierra Nevada frontal fault system toward the south and the Round Valley fault in the north. It also marks the region where right-lateral motion along the Sierras steps eastward across Owens Valley. Previous interpretations of the Coyote Warp range from a simple relay ramp, to a plunging anticline, to a series of slide blocks. Its subdued morphology has remained enigmatic in comparison with the steep footwall escarpments typical of the eastern Sierras.

We interpret the Coyote Warp as a fault-propagation fold at the northern tip of the Sierra Nevada frontal normal fault zone. This is based on: 1) the abundance of grabens and antithetic normal faults along the Sierra-Owens Valley margin between Big Pine and Bishop, 2) lack of evidence for a significant E-dipping range-front fault here, and 3) comparison of the strain distribution with other well-documented examples of normal fault propagation folds.

The northern end of the Coyote Warp has been disrupted by a NE-striking, NW-dipping normal fault along the west side of the Tungsten Hills, which displaces Late Pleistocene units and diverted several stream courses during the Late Pleistocene. The geometry and kinematics of the Tungsten Hills fault are not well explained by interaction between the Round Valley fault and the Sierra Nevada frontal normal faults. The Tungsten Hills fault is better interpreted as helping distribute right-lateral NNW shear in Owens Valley, as it steps eastward from the Sierran side of the valley south of the Coyote Warp to the White Mountains fault zone, north of the Coyote Warp. Thus the nature of the Coyote Warp has interesting implications for transtension in Owens Valley, in that the structural discontinuity at the Coyote Warp appears to have impeded northward propagation of right-lateral slip, forcing it to step eastward to the nearby White Mountains fault zone.