SURFICIAL GEOLOGY AND QUATERNARY FAULT MAP OF THE LAS VEGAS VALLEY, NEVADA

The Las Vegas Valley is home to a fast-growing metropolitan area with more than 2 million residents. The Quaternary geology of the valley impacts land use planning initiatives, water resource management, and the characterization of both seismic and flood hazards. Our new 1:50,000 scale geologic map involved the compilation of twenty published 1:24,000 scale 7.5’ quadrangles, in conjunction with new field and desktop mapping, and geochronology. The compilation utilized a variety of digital base datasets including pre-development historical aerial imagery and lidar topographic data to validate existing geologic mapping, edge match adjacent maps, and digitize new geologic linework. To facilitate the updated mapping in the largely urbanized center of Las Vegas Valley we produced a new orthophoto mosaic and digital elevation model from 1965 aerial photos using structure from motion photogrammetric software. The map compiles 130 unique, named map units from the original source mapping into a uniform list of 20 geologic units. Linework from the existing mapping was evaluated, and wherever possible the published linework was preserved, though in many locations the original linework was modified to integrate new map units, incorporate field and remote observations, update geologic interpretations, and to preserve map style consistency. This map compilation was produced in support of a recent investigation into the seismic hazard of the Las Vegas basin, with a primary goal being the review and refinement of Quaternary fault mapping and the production of a consistent characterization of surficial units displaced by the faults. The mapping was accompanied by thirty-seven new luminescence ages collected from fine-grained ground water discharge deposits of the Las Vegas Formation and alluvial fan deposits to better constrain the age of surficial deposits and the recency of fault activity. This study was perfumed in conjunction with paleoseismic investigations of the Las Vegas Valley fault system and Frenchman Mountain fault system which have yielded new constraints on fault slip rates and the age of paleo-earthquakes in Las Vegas Valley.