Geologic and Geophysical Maps of the Las Vegas 30′ × 60′ Quadrangle, Clark and Nye Counties, Nevada, and Inyo County, California By William R. Page,1 Scott C. Lundstrom,1 Anita G. Harris,1 Victoria E. Langenheim,2 Jeremiah B. Workman,1 Shannon A. Mahan,1 James B. Paces,1 Gary L. Dixon,3 Peter D. Rowley,4 B.C. Burchfiel,5 John W. Bell,6 and Eugene I. Smith7 Prepared in cooperation with the Southern Nevada Water Authority Pamphlet to accompany Scientific Investigations Map 2814 1U.S. Geological Survey, Denver, CO 2U.S. Geological Survey, Menlo Park, CA 3Southwest Geology, Inc., Blackfoot, ID 4Geologic Mapping, Inc., New Harmony, UT 5Massachussetts Institute of Technology, Cambridge, MA 6Nevada Bureau of Mines and Geology, Reno, NV 7University of Nevada, Las Vegas, NV U.S. Department of the Interior U.S. Geological Survey Contents CHAPTER A GEOLOGY OF THE LAS VEGAS 30′ × 60′ QUADRANGLE Introduction ................................................................................................................................................... 1 Methods ......................................................................................................................................................... 2 Description of Map Units............................................................................................................................. 2 Quaternary and Tertiary Rocks.......................................................................................................... 2 Gravelly Alluvium, Predominantly of Alluvial Fans ................................................................ 2 Footslope Colluvium and Alluvium ........................................................................................... 7 Fine-grained Deposits ................................................................................................................ 7 Basin-fill Deposits..................................................................................................................... 10 Volcanic Rocks .......................................................................................................................... 11 Mesozoic, Paleozoic, and Proterozoic Rocks ............................................................................... 12 Stratigraphy of the Las Vegas 30′ × 60′ Quadrangle............................................................................. 21 Proterozoic Rocks.............................................................................................................................. 21 Paleozoic Rocks ................................................................................................................................. 21 Mesozoic Rocks ................................................................................................................................. 25 Tertiary Rocks..................................................................................................................................... 26 Quaternary .......................................................................................................................................... 26 Structure of the Las Vegas 30′ × 60′ Quadrangle .................................................................................. 27 Introduction ........................................................................................................................................ 27 Mesozoic Thrust Faults..................................................................................................................... 27 Spring Mountains ..................................................................................................................... 27 Wheeler Pass Thrust....................................................................................................... 27 Lee Canyon and Macks Canyon Thrusts ..................................................................... 28 Deer Creek Thrust............................................................................................................ 28 Keystone and Red Spring Thrusts................................................................................. 28 Bird Spring Thrust............................................................................................................ 30 Sheep Range and Las Vegas Range...................................................................................... 30 Gass Peak and Valley Thrusts ....................................................................................... 30 Correlation of Thrusts .............................................................................................................. 31 Age of Thrusts ........................................................................................................................... 31 High-angle Normal and Strike-Slip Faults ..................................................................................... 32 Spring Mountains ..................................................................................................................... 32 Trough Spring Fault.......................................................................................................... 32 La Madre Fault ................................................................................................................. 32 Griffith Fault ...................................................................................................................... 32 Wheeler Graben............................................................................................................... 32 Sheep and Las Vegas Ranges ................................................................................................ 33 Las Vegas Valley Shear Zone.................................................................................................. 33 State Line and West Spring Mountains Fault Zones........................................................... 34 Cenozoic Landslide Deposits ........................................................................................................... 34 Quaternary Faults .............................................................................................................................. 35 iii Introduction ............................................................................................................................... 35 Las Vegas Valley ....................................................................................................................... 36 Pahrump Valley ......................................................................................................................... 37 References Cited ........................................................................................................................................ 37 CHAPTER B GEOPHYSICAL FRAMEWORK OF THE LAS VEGAS 30′ × 60′ QUADRANGLE Introduction ................................................................................................................................................. 45 Aeromagnetic Data .................................................................................................................................... 45 Isostatic Gravity Data................................................................................................................................. 45 Basins .......................................................................................................................................................... 47 Las Vegas Valley ................................................................................................................................ 47 Corn Creek Springs............................................................................................................................ 48 Pahrump Valley .................................................................................................................................. 48 Pre-Cenozoic Basement ............................................................................................................................ 49 Spring Mountains .............................................................................................................................. 49 Frenchman Mountain ........................................................................................................................ 49 Las Vegas Range................................................................................................................................ 49 Conclusions ................................................................................................................................................. 54 References Cited ........................................................................................................................................ 54 Figures 1. Map Sheet 1 (Index of Geologic Mapping) 2. Map Sheet 1 (Paleozoic Correlations in major thrust sheets) 3A. Map Sheet 1 (Major structures) 3B. Map Sheet 1 (Eastern Spring Mountains Structural Model 1) 3C. Map Sheet 1 (Eastern Spring Mountains Structural Model 2) 4. Pamphlet page 46, Chapter B (Index Map) 5. Map Sheet 2 (Residual Aeromagnetics) 6A. Map Sheet 2 (Basin Thickness of Las Vegas Valley) 6B. Map Sheet 2 (Basin Thickness of Pahrump Valley) 7. Map Sheet 2 (Basement Gravity with Aeromagnetic Contours) 8. Pamphlet Page 50, Chapter B (Magnetic Model) 9A. Pamphlet Page 51, Chapter B (Cross Section D–D’) 9B. Pamphlet