Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Fig. 3: Lidar hillshade showing traces of the Buffalo Valley fault (red arrows), locations of soil pits (yellow circles) and profiles (black lines labelled P1-P5). Quaternary alluvial fans include relatively old (Qfo), intermediate (Qfi), and young (Qfy) deposits. R E S U LT S A N D D I S C U S S I O N Fault traces and Quaternary alluvial fans were mapped based on inspection of lidar hillshades and field reconnaissance (Fig. 3). Our efforts focused on an ~7- km-long section of the fault where it projects away from the range front and is expressed by multiple subparallel scarps and grabens that displace alluvial fans of various ages. Alluvial fan units were differentiated primarily based on cross cutting and inset relations, relative degree of incision, and drainage patterns. The units include relatively old (Qfo), intermediate (Qfi), and young (Qfy) alluvial fans following common stratigraphic nomenclature in the Basin and Range. The distribution of these surfaces is shown on Fig. 3. In general, Qfo surfaces are characterized by deep gully dissection and rounded interfluves. Qfi surfaces are characterized by relatively flat surfaces with moderate gully dissection that are inset into Qfo deposits. Qfy deposits are confined to active channels deeply eroded (12-20 m) into Qfo and Qfi deposits in upslope areas and spread out across the piedmont downslope of the fault where they are characterized by anastomosing distributary channels. A pluvial lake existed in Buffalo Valley in the late Pleistocene (beyond the limit of the map in Fig. 3) and reached a maximum elevation of ~1412-1416 m based on the sill elevation at the eastern side of the valley. This elevation is lower than mapped fault scarps providing confidence that they are tectonic in origin, and not shoreline features.