Prepared in cooperation with the Bureau of Land Management Geophysical Framework Investigations Influencing Ground-water Resources in East-central Nevada and West-central Utah By Janet T. Watt and David A. Ponce With a section on Geologic and Geophysical Basin-by-basin Descriptions By Alan R. Wallace, Janet T. Watt, and David A. Ponce Open-File Report 2007-1163 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Watt, Janet T., and Ponce, David A., 2007, Geophysical framework investigations influencing ground-water resources in east-central Nevada and west-central Utah, with a section on Geologic and geophysical basin-by-basin descriptions by Wallace, Alan R., Watt, Janet T., and Ponce David A.: U.S. Geological Survey Open-File Report 2007-1163 [http://pubs.usgs.gov/of/2007/1163]. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. ii Contents Abstract...............................................................................................................................................................................1 Introduction........................................................................................................................................................................1 Generalized Geology......................................................................................................................................................2 Gravity and Magnetic Methodology ...........................................................................................................................3 General.............................................................................................................................................................................3 Gravity Inversion – Depth to Basement .....................................................................................................................4 Boundary Analysis of Gravity and Magnetic Sources.............................................................................................5 Discussion..........................................................................................................................................................................6 Lineaments ......................................................................................................................................................................6 Extent of Plutons.............................................................................................................................................................6 Basement Features........................................................................................................................................................7 3D Geologic Model.........................................................................................................................................................8 Geologic and Geophysical Basin-by-basin Descriptions.....................................................................................9 Basin stratigraphy and tectonics ................................................................................................................................9 Basin geophysics .........................................................................................................................................................11 Little Smoky Valley .......................................................................................................................................................11 Newark Valley...............................................................................................................................................................12 Long Valley ....................................................................................................................................................................12 Butte Valley ...................................................................................................................................................................13 Jakes Valley ..................................................................................................................................................................15 “Willow Grove” Valley.................................................................................................................................................15 Steptoe Valley ...............................................................................................................................................................16 Tippett Valley.................................................................................................................................................................18 White River Valley ........................................................................................................................................................19 Cave Valley ....................................................................................................................................................................20 Lake Valley.....................................................................................................................................................................21 Spring Valley .................................................................................................................................................................23 Snake Valley..................................................................................................................................................................25 Hamlin Valley.................................................................................................................................................................25 Discussion .....................................................................................................................................................................27 Acknowledgments..........................................................................................................................................................28 References Cited............................................................................................................................................................28 Figures Figure 1. Shaded relief topographic index map.........................................................................................................34 Figure 2. Simplified geologic map ................................................................................................................................35 Figure 3. Isostatic gravity map......................................................................................................................................36 Figure 4. Aeromagnetic map.........................................................................................................................................37 Figure 5. Depth-to-basement map ...............................................................................................................................38 Figure 6. Basement gravity map...................................................................................................................................39 iii Figure 7. Simplified three-dimensional geologic model...........................................................................................40 Figure 8. Stratigraphic column of general basin stratigraphy ................................................................................41 Plate 1. Isostatic gravity map and geophysical lineaments...................................................................................... Plate 2. Depth-to-basement map and geologic structures ....................................................................................... iv Geophysical Framework Investigations Influencing Ground-water Resources in East-central Nevada and West-central Utah By Janet T. Watt and David A. Ponce Abstract A geophysical investigation was undertaken as part of an effort to characterize the geologic framework influencing ground-water resources in east-central Nevada and west-central Utah. New gravity data were combined with existing aeromagnetic, drill-hole, and geologic data to help determine basin geometry, infer structural features, estimate depth to pre-Cenozoic basement rocks, and further constrain the horizontal extents of exposed and buried plutons. In addition, a three-dimensional (3D) geologic model was constructed to help illustrate the often complex geometries of individual basins and aid in assessing the connectivity of adjacent basins. In general, the thirteen major valleys within the study area have axes oriented