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Hudson U.S. Geological Survey Professional Paper 1608 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Bruce Babbitt, Secretary U.S. Geological Survey Charles G. Groat Director First printing December 1999 For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225 This publication is also available online at: http://greenwood.cr.usgs.gov/pub/ppapers/p1608 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data Geophysical framework of the southwestern Nevada volcanic field and hydrogeologic implications / by V.J.S. Grauch .... (et. al.). p. cm.—(U.S. Geological Survey professional paper ; 1608) Includes bibliographical references. 1. Geology, Structural—Nevada. 2. Hydrogeology— Nevada. I. Grauch, V.J.S. II. Series. QE627.5.N3 G46 2000 551.8'09793—dc21 99-054705 Contents Abstract......................................................................................................................................... 1 Introduction .................................................................................................................................. 1 Regional Setting ........................................................................................................................... 2 Hydrogeologic Background ....................................................................................................... 3 Regional Hydrology........................................................................................................... 3 Hydrogeologic Units.......................................................................................................... 3 Geophysical Background ........................................................................................................... 5 Gravity Data ....................................................................................................................... 5 Aeromagnetic Data ........................................................................................................... 7 Geophysical-Structural Domains............................................................................................... 7 Timber Mountain Domain ........................................................................................................... 11 Calderas and Caldera-Related Features ....................................................................... 11 Faults at Pahute Mesa ..................................................................................................... 13 North-Northeast-Trending Structures........................................................................... 15 Oasis Valley Basin ............................................................................................................ 15 Other Domains .............................................................................................................................. 17 Western Domain ............................................................................................................... 17 Southwestern Domain....................................................................................................... 17 Southern Domain .............................................................................................................. 31 Eastern Domain ................................................................................................................. 32 Southeastern Domain ....................................................................................................... 33 Hydrogeologic Implications........................................................................................................ 33 Regional Hydrologic and Geophysical Features .......................................................... 33 Hydrogeologic Implications West of the Nevada Test Site ....................................... 33 Acknowledgments........................................................................................................................ 35 References Cited.......................................................................................................................... 35 Figures 1. Map showing approximate extent of the southwestern Nevada volcanic field .... 2 2. Map showing major aquifer systems ............................................................................ 4 3. Map of isostatic residual gravity using a reduction density of 2,400 kg/m3 ........... 6 4. Map of reduced-to-pole aeromagnetic data ............................................................... 12 5. Map of magnetic potential data ..................................................................................... 14 6. Map showing the six geophysical-structural domains .............................................. 16 7. Map showing outlines of interpreted subsurface features ...................................... 18 8. Reduced-to-pole magnetic map of the Pahute Mesa area ....................................... 19 9. Magnetic profile model, northeast of Black Mountain .............................................. 31 10. Geologic map of Oasis Valley basin area ....................................................................