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U.S. DEPARTMENT of the INTERIOR U.S. GEOLOGICAL SURVEY GEOLOGIC MAP of the YUCCA MOUNTAIN REGION, NYE COUNTY, NEVADA by Christop

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U.S. DEPARTMENT of the INTERIOR U.S. GEOLOGICAL SURVEY GEOLOGIC MAP of the YUCCA MOUNTAIN REGION, NYE COUNTY, NEVADA by Christop U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY GEOLOGIC MAP OF THE YUCCA MOUNTAIN REGION, NYE COUNTY, NEVADA By Christopher J. Potter1 , Robert P. Dickerson2 , Donald S. Sweetkind1 , Ronald M. Drake II1, Emily M. Taylor1, Christopher J. Fridrich1 , Carma A. San Juan1, and Warren C. Day1 1U.S. Geological Survey 2S.M. Stoller Corp. 2002 Prepared in cooperation with the U.S. DEPARTMENT OF ENERGY NATIONAL NUCLEAR SECURITY ADMINISTRATION NEVADA OPERATIONS OFFICE, Interagency Agreement DE-AI08-97NV12033 Pamphlet to accompany GEOLOGIC INVESTIGATIONS SERIES I–2755 CONTENTS Abstract ..................................................................................................................... ......................1 Introduction .....................................................................................................................................1 Previous mapping ............................................................................................................. ...........4 Methods ....................................................................................................................................5 Surface geologic mapping .....................................................................................................5 Geophysical interpretation of buried structures beneath large basins ...................................... 5 Construction of cross sections ............................................................................................5 Borehole designations ................................................................................................................7 Regional geologic setting .................................................................................................................7 Stratigraphic notes ........................................................................................................................10 Proterozoic and Paleozoic stratigraphy .....................................................................................10 Tertiary stratigraphy ........................................................................................................ ........11 Quaternary stratigraphy ...................................................................................................... .....17 Caldera geology .............................................................................................................. ...............18 Claim Canyon caldera ......................................................................................................... ......18 Other calderas in the map area ............................................................................................... ...19 Structural geology .........................................................................................................................19 Late Paleozoic to Mesozoic contractional structures .................................................................19 Thrust faults in and near the map area ................................................................................19 Subsurface interpretation of thrust faults beneath the map area ........................................... 20 Striped Hills interpretation ................................................................................................. .22 Neogene structural patterns .....................................................................................................24 Structural patterns in and near the Claim Canyon caldera ...................................................24 Neogene fault patterns south of the caldera complexes ........................................................ 24 Amargosa Desert ...............................................................................................................27 Timing of Neogene deformation .......................................................................................... 28 Description of map units .................................................................................................................29 References cited .............................................................................................................................39 i FIGURES Figure 1. Map showing location of map area and selected Neogene geologic features in the surrounding area ..........................................................................................................................2 Figure 2. Shaded relief map of the geologic map area, showing place names referred to in text............. 3 Figure 3. Map showing areas covered by geophysical studies used to infer concealed structures in the map area................................................................................................................ .............6 Figure 4. Map showing location of thrust faults in the map area and the surrounding region................ 9 Figure 5. Diagrammatic geologic section along cross section D–D' showing hypothetical configuration of thrust faults and inferred detachment surface within the Wood Canyon Formation ................................................................................................................................21 Figure 6. Diagram showing sequential development of thrust faults in a hypothetical stacked-ramp geometry .................................................................................................................................23 TABLES Table 1. Borehole designations used on the geologic map of the Yucca Mountain region, Nevada........ 8 CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS Multiply by To obtain millimeter (mm) 0.03937 inch centimeter (cm) 0.3937 inch meter (m) 3.281 foot kilometer (km) 0.6214 mile Sea level: In this report sea level refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum derived from a general adjustment of the first-order-level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. The following terms and abbreviations also are used in this report: ka thousands of years before present Ma millions of years before present ii ABSTRACT steeply dipping faults that strike radially to the caldera and bound south-dipping blocks of volcanic rock. Yucca Mountain, Nye County, Nev., has been South and southeast of the Claim Canyon identified as a potential site for underground storage caldera, in the area that includes Yucca Mountain, the of high-level radioactive waste. This geologic map Neogene fault pattern is dominated by closely compilation, including all of Yucca Mountain and spaced, north-northwest- to north-northeast-striking Crater Flat, most of the Calico Hills, western Jackass normal faults that lie within a north-trending graben. Flats, Little Skull Mountain, the Striped Hills, the This 20- to 25-km-wide graben includes Crater Flat, Skeleton Hills, and the northeastern Amargosa Yucca Mountain, and Fortymile Wash, and is Desert, portrays the geologic framework for a satu- bounded on the east by the “gravity fault” and on rated-zone hydrologic flow model of the Yucca the west by the Bare Mountain fault. Both of these Mountain site. Key geologic features shown on the faults separate Proterozoic and Paleozoic sedimentary geologic map and accompanying cross sections in- rocks in their footwalls from Miocene volcanic rocks clude: (1) exposures of Proterozoic through Devo- in their hanging walls. nian strata, inferred to have been deformed by re- Stratigraphic and structural relations at Yucca gional thrust faulting and folding, in the Skeleton Mountain demonstrate that block-bounding faults Hills, Striped Hills, and Amargosa Desert near Big were active before and during eruption of the 12.8– Dune; (2) folded and thrust-faulted Devonian and 12.7 Ma Paintbrush Group, and significant motion on Mississippian strata, unconformably overlain by these faults continued until after the 11.6 Ma Rainier Miocene tuffs and lavas and cut by complex Neogene Mesa Tuff was deposited. North of Crater Flat, in fault patterns, in the Calico Hills; (3) the Claim and near the Claim Canyon caldera, most of the tilt- Canyon caldera, a segment of which is exposed ing of the volcanic section predated the 11.6 Ma north of Yucca Mountain and Crater Flat; (4) thick, Rainier Mesa Tuff. In contrast, geologic relations in densely welded to nonwelded ash-flow sheets of the central and southern Yucca Mountain indicate that Miocene southwest Nevada volcanic field exposed in much of the stratal tilting there occurred after 11.6 normal-fault-bounded blocks at Yucca Mountain; (5) Ma, probably synchronous with the main pulse of upper Tertiary and Quaternary basaltic cinder cones vertical-axis rotation that occurred between 11.6 and and lava flows in Crater Flat and at southernmost 11.45 Ma. Yucca Mountain; and (6) broad basins covered by Beneath the broad basins, such as Crater Flat, Quaternary and upper Tertiary surficial deposits in Jackass Flats, and the Amargosa Desert, faults are in- Jackass Flats, Crater Flat, and the northeastern ferred from geophysical data. Geologic and geo- Amargosa Desert, beneath which Neogene normal physical data imply the presence of the large-offset, and strike-slip faults are inferred to be present on the east-west striking Highway 95 fault beneath surficial basis of geophysical data and geologic map patterns. deposits along the northeast margin of the Amargosa A regional thrust belt of late Paleozoic or Desert, directly south of Yucca Mountain
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