UCLA

The Searles Valley region of southeastern California exhibits a series of northeasterly trending folds that are anomalously oriented when viewed in the context of the current regional stress field, where the principal compressive stress is oriented from the northeast and southwest. This region also marks a complex zone of deformation, as the Blackwater fault of the Eastern California Shear Zone (ECSZ) appears to terminate at its intersection with the Browns Valley/Ranch fault zone, 5 km south of the Garlock fault. The presence of the northeasterly trending Christmas Canyon anticline near the junction of these three fault systems has led to the inference that regional compression directed from the northwest and southeast may have occurred during the last 640,000 years. To assess the style of deformation associated with the interaction of these three fault zones, a geologic survey consisting of geologic mapping, remote sensing and absolute-dating techniques was conducted within the northeastern Lava Mountains, immediately south of the Garlock fault. The study area, informally designated as western Christmas Canyon, exhibits a series of northeasterly trending structures that have deformed and offset lacustrine deposits of the middle Pleistocene Christmas Canyon Formation. These northeasterly striking faults, exhibit displacements suggestive of sinistral shear, and are oriented on average 22 degrees counterclockwise to the trace of the Garlock fault in southern Searles Valley. The orientation and mode of deformation attributed to these faults implies that they may have formed as Riedel shears to the sinistral Garlock fault zone, and thus likely formed during a period of northeast-southwest directed regional compression. Conversely, a single northeast-trending synclinal structure within western Christmas Canyon implies regional compression nearly orthogonal to the adequate orientation for driving sinistral shear along the Garlock fault zone. The results obtained from the geologic survey of the western Christmas Canyon region imply that the Garlock fault has sinistrally offset two alluvial fan surfaces from their source drainage during the late Holocene, and that a period of northwest-southeast directed compression most likely did not occur since the deposition of the middle Pleistocene Christmas Canyon Formation. As a result, the formation of northeasterly trending folds within the Christmas Canyon Formation is inferred to be attributed to deformation associated with slip along Riedel shears of the Garlock fault zone, or as a result of distributed deformation associated with the termination of northwesterly striking dextral faults of the Eastern California Shear zone or P' shears to the Garlock fault.