Quaternary Deformation of the Hog Ranch-Naneum Anticline Region, Northeast Kittitas Valley, Washington

Abstract

Geomorphic evaluation of the northeastern Kittitas Valley and Hog Ranch-Naneum Anticline (HRNA) region provides new insight into the recent deformation and uplift by Quaternary faults along the northern range front of Kittitas Valley. I conducted LiDAR and landform mapping as well as a suite of geomorphic analyses to assess recent faulting in northeastern Kittitas Valley potentially linked to Quaternary deformation of the HRNA area. Upon generation of normalized channel steepness (Ksn) maps, the northeastern basin front was identified as a starting point for additional geomorphic analyses, LiDAR mapping and focused field truthing/mapping. I identified a flight of six strath river terraces near the entrance of Coleman Creek into Kittitas Valley. I also identified knickpoints and knickzones along the southern basin front which I was able to correlate to the knickpoint groupings along Coleman Creek. Based on geomorphic evidence and LiDAR mapping two fault scarps were identified; the Facet fault located at the base of the range front and the Dead Coyote fault located ~2 km south of the range front. Regional geologic mapping and aeromagnetic data suggests that initial tectonic uplift along the HRNA predates the Yakima folds. Exact ages of newly identified faults are unknown. The presence of uplifted strath surfaces within Kittitas Valley suggests a more recent deformation history based on the premise that the landscape within the fold province and HRNA was reset to relatively level relief ~15.6 Ma following the emplacement of the Grand Ronde Basalt member of the CRBG; deformation seems to have continued into the Quaternary (Kelsey et al., 2017 and Reidel, 1989).