ACTIVE INTERNAL DEFORMATION OF THE SIERRA NEVADA MICROPLATE ON THE KERN CANYON FAULT AT SODA SPRING, TULARE COUNTY, CALIFORNIA

The Kern Canyon fault (KCF) represents a major tectonic and physiographic boundary in the southern Sierra Nevada of east-central California. Previous investigations of the KCF underscore its importance as a late Cretaceous and Neogene shear zone in the tectonic development of the southern Sierra Nevada. Study of the late Quaternary history of activity, however, has been confounded by the remote nature of the KCF and deep along-strike exhumation within the northern Kern River drainage, driven by focused fluvial and glacial erosion. Recent acquisition of airborne LiDAR (light detection and ranging) topography along the ~140 km length of the KCF provides a comprehensive view of the active surface trace. High-resolution, LiDAR-derived digital elevation models (DEMs) for the northern KCF enable identification of previously unrecognized offsets of late Quaternary moraines near Soda Spring (36.345, -118.408). Predominately north-striking fault scarps developed on the Soda Spring moraines display west-side-up displacement and lack a significant sense of strike-slip separation, consistent with detailed mapping and trenching along the entire KCF. Scarp-normal topographic profiling derived from the LiDAR DEMs suggests normal displacement of at least 2.8 +0.6/-0.5 m of the Tioga terminal moraine crest. Cosmogenic ¹⁰Be exposure dating of Tioga moraine boulders yields a tight age cluster centered around 18.1 ± 0.5 ka (n=6), indicating a minimum normal-sense fault slip-rate of ~0.1-0.2 mm/yr over this period. Taken together, these results provide clear documentation of late Quaternary activity on the KCF and highlight its role in accommodating extension and internal deformation of the southern Sierra Nevada microplate.