In Revision, GEOMORPHOLOGY

Late Quaternary offset on the Big Pine fault, southern California

Stephen B. DeLong Department of Geosciences, University of Arizona, 1040 E 4th

Street, Tucson AZ 85721, USA

Scott A. Minor United States Geological Survey, Denver CO 80225, USA

Lee J. Arnold Oxford Luminescence Research Group, School of Geography and the

Environment, University of Oxford, Mansfield Rd, Oxford OX1 3TB,

UK

Keywords: landscape development; neotectonics; optical dating; Big Pine fault

ABSTRACT

Determining late-Quaternary offset rates on specific faults within the dense structural array of the western Transverse Ranges requires the identification of offset and datable geomorphic or stratigraphic markers. Here we report an estimate of fault-slip rate on the Big Pine fault in the Upper Cuyama Valley, California, and the geomorphology related to the fault. Deposition of coarse alluvium and debris sourced from the Pine Mountain massif occurred near the southern margin of the Cuyama structural basin at or near the elevation of the Cuyama River between 25 and 14 ka. This alluvial deposit was subsequently offset ~10 m vertically by the Big Pine fault after termination of deposition, providing a latest Quaternary vertical slip-rate estimate of ~0.7 m/ky for the Big Pine fault in the upper Cuyama Valley. The Big Pine fault has no confirmed record of historic rupture; however based on our results, we suggest the likelihood of multiple reverse-slip rupture events since ~14 ka.

Email: sdelong@geo.arizona.edu