THE ROLE OF THE GRIZZLY VALLEY FAULT ZONE IN ACCOMMODATING SHEAR OF THE NORTHERN WALKER LANE, NE CALIFORNIA, USA

The northern Walker Lane is a zone of predominantly NW-trending right-lateral shear between the Sierra Nevada and the Basin and Range. A series of NW-trending right-lateral faults including the Pyramid Lake, Warm Springs Valley, Honey Lake, and Mohawk Valley fault zones are known to accommodate a significant portion of the NW-directed shear of the northern Walker Lane. The Grizzly Valley fault zone is subparallel to these faults and exhibits gross geomorphic features consistent with active right-lateral strike-slip motion. The fault zone extends ~55 km from near Loyalton to the NE-facing slope of Mount Ingalls. The zone shows little vertical relief across Sierra Valley where it is expressed as tonal lineaments and spring alignments that coincide with changes in drainage patterns across the valley floor. Enclosed depressions are aligned along the fault in Big Grizzly Creek canyon. The fault continues along the edge of Grizzly Valley where it apparently continues partially submerged beneath Lake Davis reservoir. The fault crosses over Bagley Pass to the NE-facing slope of Turner Ridge, where it is expressed as a continuous escarpment aligned with bedrock channels consistently offset or deflected in a right-lateral sense. The Lovejoy basalt (~16 Ma) appears to be offset right-laterally by the fault on the NE-facing slope of Turner Ridge, and apparent escarpments in undated Quaternary lateral moraines along the NE-facing slope of Mount Ingalls may reflect recent fault motion. In summary, numerous geologic and geomorphic indicators along the Grizzly Valley fault zone suggest recent right-lateral strike-slip motion, and the Grizzly Valley fault may accommodate a signficant portion of right-lateral slip in the northernmost Walker Lane.