GSA Connects 2021 in Portland, Oregon

Paper No. 195-5
Presentation Time: 2:30 PM-6:30 PM


BURKEY, Jordan D., Earth and Ocean Sciences, University of North Carolina at Wilmington, Wilmington, NC 28403, HAPROFF, Peter J., Earth and Ocean Sciences, University of North Carolina Wilmington, 601 S College Rd, Wilmington, NC 28403-3201 and HOOKER, Julian, 913A Bryan Ave, Wilmington, NC 28403-4217

We present new detailed and regional-scale Quaternary surficial geologic maps of the Eureka Valley fault and other normal faults located along the margins of Eureka Valley in eastern California. The ~30-km-long, N- to NE-striking and W- to NW-dipping Eureka Valley fault, located between the Horse Thief Hills to the north and Steel Pass to the south, is the dominant structure in the region that juxtaposes the Eureka Valley graben to the west from the Last Chance Range horst block to the east. The Eureka Valley fault consists of ~1-5, closely spaced, subparallel fault strands that are expressed as: (1) mostly W- to NW-facing scarps with heights and lengths up to ~15 m and ~2 km, respectively, mostly within early Holocene(?) (abbr. Qfyo) and older alluvial fan deposits, and (2) exposed fault surfaces along the contact between footwall Paleozoic bedrock strata and hanging-wall Quaternary and Neogene alluvial fan deposits. Few strands of the Eureka Valley fault displace late Holocene(?) alluvial fan deposits (abbr. Qfy) as ~1-m-high and <1-km-long scarps. Exposed fault surfaces along bedrock-alluvium contacts form triangular facets and contain slickenlines indicative of dip-slip motion. Series of more widely spaced brittle normal faults were mapped cutting Paleozoic bedrock within the footwall of the main Eureka Valley fault trace. Near the axis of Eureka Valley, west of the main Eureka Valley fault trace, we identified several subsidiary normal faults as <1-km-long, W- and E-facing scarps within early Holocene(?) (abbr. Qfyo) and middle Pleistocene(?) (Qfo) alluvial fan deposits. In addition, we mapped segments of two ~5-10-km-long, NE-striking and NW-dipping normal faults located along the western margin of Eureka Valley, oblique to the N-trending basin-Saline Range interface. These two faults are expressed as ~1-3, <10-m-high and ~3-5-km-long, NW-facing scarps within late Holocene(?) (abbr. Qfy) and older alluvial fan deposits. Near the interior of the Saline Range, the normal faults are mostly buried beneath active alluvial drainages (abbr. Qa) and sand deposits (abbr. Qs) and are inferred to parallel the margins of Mesozoic and Paleozoic bedrock exposures. Neither these normal faults nor the Eureka Valley fault display evidence of recent strike-slip motion. Furthermore, segments of the Eureka Valley fault truncate brittle strike-slip faults that cut through the Last Chance Range. These observations suggest that the most recent phase of deformation in the Eureka Valley region was purely extensional.