On and Off Shore Studies of the Trench Canyon Fault Zone, Mono Lake, Northeastern California

The northern Mono Basin, located on the California-Nevada border, lies geographically within the tectonically active central Walker Lane fault system (figure 1), a region currently responsible for accommodating ∼ 10 mm/yr of right lateral slip produced by relative motion between the Pacific and North American plates. I conducted studies on a previously hypothesized but unexamined ∼ 20 km long fault zone (the Trench Canyon Fault Zone (TCFZ)) spanning from Cedar Hill Volcano northeast of Mono Lake to Negit Island within the lake. Onshore studies of the lineament include intensive analysis of: aerial imagery, relict shorelines and their elevations, scarp profiles and field observations. We also conducted seismic surveys of the lake bottom with the aid of the United States Geologic Survey, and side scan sonar surveys were conducted by Dr. Milene Cormier and Hal Johnson from the University of Missouri - Columbia.;Onshore studies reveal that the northern most lineaments in the study area (which was deemed the northern TCFZ) are not in fact fault induced scarps, but rather wave cuts incised during the desiccation of ancient Lake Russell (the parent body of modern day Mono Lake) onto a topographic high. Additionally, no positive evidence of faulting could be discerned spanning from the present day shoreline of Mono Lake northward on land for approximately 4.5 kilometers. Constrained within these northern and southern brackets are sets of discontinuous, en echelon fault induced lineaments, with a known component of normal faulting. Spanning a total of ~6.5 km at an approximate strike of N40E, I propose the onshore component of the TCFZ has been active within the last 3500 -- 12000 years.;Offshore studies and seismic analysis revealed a significant number of faults within Mono Lake. I identified twenty-one potential fault features on 5 of the 9 traverses conducted and analyzed in the study area, revealing dip slip components of offset ranging from ∼ 0.5 meters to greater than 2 meters. However, due to shallow water, natural lake hazards, distances between seismic survey lines, and the discontinuity of interpreted faulting events, I found linear correlation between individual faulting events to be difficult and therefore speculative, as was any association between offshore faulting and the onshore culmination of the TCFZ.;The TCFZ can be positively and confidently identified as a ∼ 6.5 km long set of discontinuous onshore faults, a fraction of the originally proposed ∼ 20 km lineament theorized to span onshore from Cedar Hill Volcano near the California- Nevada border offshore into modern day Mono Lake.