AbstractsEarth & Environmental Science

The geology of the Singleton anticline and along-strike change of the San Gorgonio Pass strand, San Andreas Fault from emergent thrust to anticline, near Calimesa, CA

by Kaitlyn Jones

Institution: California State University – Northridge
Year: 2016
Keywords: Geology Singleton Anticline; Dissertations, Academic  – CSUN  – Geological Sciences.
Posted: 02/05/2017
Record ID: 2065010
Full text PDF: http://hdl.handle.net/10211.3/178805


ABSTRACT The western terminus of the San Gorgonio Pass fault zone: Structural expression and possible linkage and slip transfer with neighboring faults By: Kaitlyn L. Jones Master of Science in Geology The San Gorgonio Pass fault zone (SGPFZ) and its eastern extension, the Garnet Hill Fault, can be traced for 75 km from Calimesa to the Indio Hills. The eastern end of the fault system merges with the Banning strand of the San Andreas Fault via a compressive left stepover in the fault system. However, the western terminus of the SGPFZ and its possible connection with nearby faults is poorly understood. This study presents the results of a large-scale mapping project and detailed evaluation of B4 LiDAR data at the western terminus near the town of Calimesa, CA. Mapping shows that the fault terminates in an asymmetric, open fold that verges south above a north-dipping blind thrust. Clast-counts conducted at five locations on the fold consist of igneous clasts, mainly felsic granites, diorites and volcanic porphyries. Secondary, up-on-the-north highangle faults reside in the hanging wall of the blind thrust. The blind thrust emerges 5 km to the east in Cherry Valley where distinct fault scarps displace old alluvium across 3-20 m scarps. The fold at Calimesa is defined two ways. Bedding in the Plio-Pleistocene San Timoteo Formation defines a gently west-plunging fold with a slightly steeper south limb. Quaternary alluvium angularly unconformably overlies the San Timoteo strata and is also asymmetrically folded, defining a gently west-plunging, south-vergent fold. The core of the fold is readily visible in color satellite images where it is bounded by the ovalix shaped limit of a distinct, poorly consolidated, red-orange soil, commonly developed atop the Quaternary alluvium. Slope maps of the B4 data also help define the fold showing relatively high-relief areas in the core of the fold and low-relief surfaces associated with the Quaternary alluvium at the fold???s margins. The SGPFZ thus appears to terminate as an asymmetric fold above a blind thrust. It is interesting to note that the Singleton Anticline is central to and lies <3 km from the down-to-the-southeast Crafton Hills and Beaumont Plain fault zones. We envision that these faults are linked to the SGPFZ and help transfer slip from San Gorgonio Pass on the east to the San Bernardino strand San Andreas and San Jacinto faults. If accurate, this may provide connections that facilitate San Andreas ruptures through San Gorgonio Pass. Advisors/Committee Members: Yule, John D (advisor), Pedone, Vicki (committee member).