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At least 325 records · Page 18Linked to original sources
USGS1955

Geology of the northern Black Hills bentonite mining district

Extensive deposits of bentonite are present in the Cretaceous sedimentary rock strata cropping out on the northern flank of the Black Hills. These deposits have been the subject of a study by the U.S. Geological Survey as part of the program of the Department of the Interior for appraisal of natural resources of the Missouri River Basin. This report contains information concerning the geology of the bentonite deposits of the Northern Black Hills district. An attempt is made to explain some of the relations that exist between the physical properties and the mineralogical characteristics of the bentonite. Consideration is given to the occurrence of bentonite deposits and different types of sedimentary rocks and to depositional and post-depositional conditions which these rocks reveal. Evidence for sources of ancestral materials and conditions of alteration are discussed.

Black Hills↗
USGS1999

Archive of 15 cubic inch water gun data collected during USGS Cruise ALPH98013, New York Bight, 10-22, September, 1998

Background This CD-ROM contains copies of the navigation and field water gun subbottom data collected aboard the F/V Alpha & Omega II. The USGS Cruise ALPH98013 was conducted from 10-22 September, 1998, and is a collaborative involving the U.S Army Corps of Engineers, New York District and the United States Geological SurveyCoastal and Marine Geology Program, Woods Hole Field Center. In 1995, the USGS, in cooperation with the U.S Army Corps of Engineers (USACOE), New York District, began a program to generate reconnaissance maps of the sea floor offshore of the New York-New Jersey metropolitan area, one of the most populated coastal regions of the United States. The goal of this mapping program is to provide a regional synthesis of the sea-floor environment, including a description of sedimentary environments, sediment texture, sea-floor morphology, and geologic history to aid in understanding the impacts of anthropogenic activities, such as ocean dumping. This mapping effort differs from previous studies of this area by obtaining digital, sidescan sonar images that cover 100 percent of the sea floor. This investigation was motivated by the need to develop an environmentally acceptable solution for the disposal of dredged material from the New York - New Jersey Port, by the need to identify potential sources of sand for renourishment of the southern shore of Long island, and by the opportunity to develop a better understanding of the transport and long-term fate of contaminants by investigations of the present distribution of materials discharged into the New York Bight over the last 100+ years (Schwab and others, 1997). Sidescan-sonar data collected during USGS Cruises Seax95007 and Seax96004 (May 1995 and May 1996, respectively) were digitally mosaicked to provide a base suitable for use in Geographic Information Systems of the New York Bight Apex region. During USGS Cruise Alph98013, supplemental sidescan sonar and seismic reflection data were collected within the New York Bight Apex region, primarily to augment the seismic reflection portion of the mapping project. Additional sidescan sonar and seismic reflection data were collected east of the Seax95007 and Seax96004 survey areas. These data abut sidescan sonar and seismic reflection data collected off the Southern Long Island shoreline during USGS Cruises Dian96040, Dian97011, and Dian97032 (September 1996, May 1997, October 1997, respectively).

Open-File Report↗
USGS2000

A paleolatitude approach to assessing surface temperature history for use in burial heating models

Calculations using heat flow theory as well as case histories show that over geologic time scales (10 6 years), changes in mean annual surface temperature (T s ) on the order of 10°C penetrate kilometers deep into the crust. Thus, burial heating models of sedimentary basins, which typically span kilometers in depth and persist over geological time frames, should consider T s history to increase their accuracy. In any case, T s history becomes important when it changes enough to be detected by a thermal maturation index like vitrinite reflectance, a parameter widely used to constrain burial heating models. Assessment of the general temperature conditions leading to petroleum generation indicates that changes in T s as small as 6°C can be detected by vitrinite reflectance measurements. This low temperature threshold indicates that oil and gas windows can be significantly influenced by T s history. A review of paleoclimatic factors suggests the significant and geologically resolvable factors affecting T s history are paleolatitude, long-term changes between cool and warm geological periods (climate mode), the degree to which a basin is removed from the sea (geographic isolation), and elevation or depth relative to sea level. Case studies using geologically realistic data ranges or different methods of estimating T s in a burial heating model indicate a significant impact of Ts when: (1) continental drift, subduction, tectonism and erosion significantly change paleolatitude, paleoaltitude, or paleogeography; (2) strata are at, or near, maximum burial, and changes in T s directly influence maximum burial temperature; and (3), when a significant change in T s occurs near the opening or closing of the oil or gas windows causing petroleum generation to begin or cease. Case studies show that during the burial heating and petroleum generation phase of basin development changes in climate mode alone can influence T s by about 15°C. At present, T s changes from the poles to the equator by about 50°C. Thus, in extreme cases, continental drift alone can seemingly produce T s changes on the order of 50°C over a time frame of 107 years.

International Journal of Coal Geology↗
USGS2017

A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Española Basin, Rio Grande rift, New Mexico

A comprehensive survey of geologic structures formed in the Earth’s brittle regime in the eastern Española Basin and flank of the Rio Grande rift, New Mexico, reveals a complex and protracted record of multiple tectonic events. Data and analyses from this representative rift flank-basin pair include measurements from 53 individual fault zones and 22 other brittle structures, such as breccia zones, joints, and veins, investigated at a total of just over 100 sites. Structures were examined and compared in poorly lithified Tertiary sediments, as well as in Paleozoic sedimentary and Proterozoic crystalline rocks. Data and analyses include geologic maps; field observations and measurements; orientation, kinematic, and paleostress analyses; statistical examination of fault trace lengths derived from aeromagnetic data; mineralogy and chemistry of host and fault rocks; and investigation of fault versus bolide-impact hypotheses for the origin of enigmatic breccias found in the Proterozoic basement rocks. Fault kinematic and paleostress analyses suggest a record of transitional, and perhaps partitioned, strains from the Laramide orogeny through Rio Grande rifting. Normal faults within Tertiary basin-fill sediments are consistent with more typical WNW-ESE Rio Grande rift extension, perhaps decoupled from bedrock structures due to strength contrasts favoring the formation of new faults in the relatively weak sediments. Analyses of the fault-length data indicate power-law length distributions similar to those reported from many geologic settings globally. Mineralogy and chemistry in Proterozoic fault-related rocks reveal geochemical changes tied to hydrothermal alteration and nearly isochemical transformation of feldspars to clay minerals. In sediments, faulted minerals are characterized by mechanical entrainment with minor secondary chemical changes. Enigmatic breccias in rift-flanking Proterozoic rocks are autoclastic and isochemical with respect to their protoliths and exist near shatter cones believed to be related to a previously reported pre-Pennsylvanian impact event. A weak iridium anomaly is associated with the breccias as well as adjacent protoliths, thus an impact shock wave cannot be ruled out for their origin. Major fault zones along the eastern rift-flank mountain front are discontinuous and unlikely to impede regional groundwater flow into Española Basin aquifers. The breccia bodies are not large enough to constitute aquifers, and no fault- or breccia-related geochemical anomalies were identified as potential contamination sources for ground or surface waters. The results of this work provide a broad picture of structural diversity and tectonic evolution along the eastern flank of the central Rio Grande rift and the adjacent Española Basin representative of the rift as a whole and many rifts worldwide.

New Mexico↗
USGS1993

Characterizing the hydrogeologic framework of the Death Valley region, Southern Nevada and California

Three-dimensional (3-D) hydrogeologic modeling of the complex geology of the Death Valley region requires the application of a number of Geoscientific Information System (GSIS) techniques. This study, funded by United States Department of Energy as a part of the Yucca Mountain Project, focuses on an area of approximately 100,000 square kilometers (three degrees of latitude by three degrees of longitude) and extends up to ten kilometers in depth. The geologic conditions are typical of the Basin and Range province; a variety of sedimentary and igneous intrusive and extrusive rocks have been subjected to both compressional and extensional deformation. GSIS techniques allow the synthesis of geologic, hydrologic and climatic information gathered from many sources, including satellite imagery and published maps and cross-sections. Construction of a 3-D hydrogeological model is possible with the combined use of software products available from several vendors, including traditional GIS products and sophisticated contouring, interpolation, visualization, and numerical modeling packages.

Conference Paper↗
USGS2022

The dynamic floor of Yellowstone Lake, Wyoming, USA: The last 14 k.y. of hydrothermal explosions, venting, doming, and faulting

Hydrothermal explosions are significant potential hazards in Yellowstone National Park, Wyoming, USA. The northern Yellowstone Lake area hosts the three largest hydrothermal explosion craters known on Earth empowered by the highest heat flow values in Yellowstone and active seismicity and deformation. Geological and geochemical studies of eighteen sublacustrine cores provide the first detailed synthesis of the age, sedimentary facies, and origin of multiple hydrothermal explosion deposits. New tephrochronology and radiocarbon results provide a four-dimensional view of recent geologic activity since recession at ca. 15–14.5 ka of the >1-km-thick Pinedale ice sheet. The sedimentary record in Yellowstone Lake contains multiple hydrothermal explosion deposits ranging in age from ca. 13 ka to ~1860 CE. Hydrothermal explosions require a sudden drop in pressure resulting in rapid expansion of high-temperature fluids causing fragmentation, ejection, and crater formation; explosions may be initiated by seismicity, faulting, deformation, or rapid lake-level changes. Fallout and transport of ejecta produces distinct facies of subaqueous hydrothermal explosion deposits. Yellowstone hydrothermal systems are characterized by alkaline-Cl and/or vapor-dominated fluids that, respectively, produce alteration dominated by silica-smectite-chlorite or by kaolinite. Alkaline-Cl liquids flash to steam during hydrothermal explosions, producing much more energetic events than simple vapor expansion in vapor-dominated systems. Two enormous explosion events in Yellowstone Lake were triggered quite differently: Elliott’s Crater explosion resulted from a major seismic event (8 ka) that ruptured an impervious hydrothermal dome, whereas the Mary Bay explosion (13 ka) was triggered by a sudden drop in lake level stimulated by a seismic event, tsunami, and outlet channel erosion.

Wyoming↗
USGS1979

Stratigraphy and depositional environments of Baltimore Canyon Trough

The Baltimore Canyon Trough, lying offshore from the United States Middle Atlantic States, contains a thickness of at least 14 km of marine and nonmarine sedimentary rocks. One deep offshore stratigraphic test (COST B-2 well), several wells on the coastal plain, 18 shallow core holes (Deep Sea Drilling Project, Atlantic Slope Project, and Atlantic Margin Coring Project) on the continental shelf and slope, and scattered oceanographic cores and dredgings provide rich foraminiferal assemblages from which the geologic age and depositional environments have been determined. The oldest sedimentary rocks penetrated are Upper Jurassic terrigenous sandstone and shale, which are interspersed with shallow-marine limestone. Lower Cretaceous rocks, where penetrated, are also chiefly terrigenous sandstone and shale, but Upper Cretaceous rocks are progressively more marine. Paleogene strata reflect even deeper marine conditions (bathyal carbonate deposits in the B-2 well). In the Neogene, terrigenous clastic deposits replaced the Paieogene carbonate sequences throughout the trough. Deposition began with thick (>800 m) deltaic beds in the Miocene and Pliocene and culminated in sandy and, in many places, nonfofesiHferous strata of the Pleistocene shelf. Surprisingly thick (>300 m) silty and sandy clay composes the Pleistocene section on the continental slope. These stratigraphic and paleoecologic relations are graphically illustrated in eight geologic cross sections parallel with and perpendicular to the axis of the trough.

Mid-Atlantic United States↗
USGS2006

Digital database of the geologic map of the Island of Hawai'i

This online publication (DS 144) provides the digital database for the printed map by Edward W. Wolfe and Jean Morris (I-2524-A; 1996). This digital database contains all the information used to publish U.S. Geological Survey Geologic Investigations Series I-2524-A (available only in paper form; see http://pubs.er.usgs.gov/pubs/i/i2524A ). The database contains the distribution and relationships of volcanic and surficial-sedimentary deposits on the island of Hawai‘i. This dataset represents the geologic history for the five volcanoes that comprise the Island of Hawai'i. The volcanoes are Kohala, Mauna Kea, Hualalai, Mauna Loa and Kīlauea. This database of the geologic map contributes to understanding the geologic history of the Island of Hawai‘i and provides the basis for understanding long-term volcanic processes in an intra-plate ocean island volcanic system. In addition the database also serves as a basis for producing volcanic hazards assessment for the island of Hawai‘i. Furthermore it serves as a base layer to be used for interdisciplinary research. This online publication consists of a digital database of the geologic map, an explanatory pamphlet, description of map units, correlation of map units diagram, and images for plotting. Geologic mapping was compiled at a scale of 1:100,000 for the entire mapping area. The geologic mapping was compiled as a digital geologic database in ArcInfo GIS format.

Hawai'i↗
USGS2018

2018 report on incorporating sedimentary basin response into the design of tall buildings in Seattle, Washington

On March 22, 2018, the Seattle Department of Construction and Inspections (SDCI) and the U.S. Geological Survey (USGS) convened a workshop of engineers and seismologists to provide guidance on incorporating sedimentary basin response into the design of tall buildings in Seattle. This workshop provided recommendations that build on those from a March 2013 workshop (Chang and others, 2014), primarily based on new results from 3-D simulations of magnitude (M) 9 Cascadia earthquakes (The M9 Project). Susan Chang, a geotechnical engineer with the Seattle Department of Construction and Inspections, organized and led the workshop; Art Frankel (USGS) assisted in constructing the agenda. The workshop agenda and attendees are provided in the appendix. The attendees represented a wide range of expertise, including seismologists with expertise in ground motions and basin response, geotechnical engineers, and structural engineers. Their professional experience included working on local projects related to the design of long-period structures; peer reviewing ground motions for performance-based design of high-rises in Seattle; researching basin response in academic, government and industry settings; developing ground motion models; and representing local and national structural engineering organizations. In this report, we summarize the technical presentations, key discussion points, and recommendations from the workshop.

Washington↗
USGS2011

Geologic map of the Cochiti Dam quadrangle, Sandoval County, New Mexico

The Cochiti Dam quadrangle is located in the southern part of the Española Basin and contains sedimentary and volcanic deposits that record alluvial, colluvial, eolian, tectonic and volcanic processes over the past seventeen million years. The geology was mapped from 1997 to 1999 and modified in 2004 to 2008. The primary mapping responsibilities were as follows: Dethier mapped the surficial deposits, basin-fill sedimentary deposits, Miocene to Quaternary volcanic deposits of the Jemez volcanic field, and a preliminary version of fault distribution. Thompson and Hudson mapped the Pliocene and Quaternary volcanic deposits of the Cerros del Rio volcanic field. Thompson, Minor, and Hudson mapped surface exposures of faults and Hudson conducted paleomagnetic studies for stratigraphic correlations. Thompson prepared the digital compilation of the geologic map. The mapped distribution of units is based primarily on interpretation of 1:16,000-scale, color aerial photographs taken in 1992, and 1:40,000-scale, black-and-white, aerial photographs taken in 1996. Most of the contacts on the map were transferred from the aerial photographs using a photogrammetric stereo-plotter and subsequently field checked for accuracy and revised based on field determination of allostratigraphic and lithostratigraphic units. Determination of lithostratigraphic units in volcanic deposits was aided by geochemical data, 40 Ar/ 39 Ar geochronology, aeromagnetic and paleomagnetic data. Supplemental revision of mapped contacts was based on interpretation of USGS 1-meter orthoimagery.

New Mexico↗
USGS2012

California State Waters Map Series — Hueneme Canyon and vicinity, California

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California's State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Hueneme Canyon and vicinity map area lies within the eastern Santa Barbara Channel region of the Southern California Bight. The area is part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation - at least 90° - since the early Miocene has been proposed for the Western Transverse Ranges, and the region is presently undergoing north-south shortening. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area, which is offshore of the Oxnard plain and west of and along the trend of the south flank of the Santa Monica Mountains, lies at the east end of the Santa Barbara littoral cell, characterized by west-to-east littoral transport of sediment derived mainly from coastal watersheds. The Hueneme Canyon and vicinity map area in California's State Waters is characterized by two major physiographic features: (1) the nearshore continental shelf, and (2) the Hueneme and Mugu Submarine Canyon system, which, in the map area, includes Hueneme Canyon and parts of three smaller, unnamed headless canyons incised into the shelf southeast of Hueneme Canyon. The shelf is underlain by tens of meters of interbedded upper Quaternary shelf, estuarine, and fluvial deposits that formed as sea level fluctuated in the last several hundred thousand years. Hueneme Canyon extends about 15 km offshore from its canyon head near the dredged navigation channel of the Port of Hueneme. The canyon is relatively deep (about 150 m at the California's State Waters limit) and steep (canyon flanks as steep as 25° to 30°). Historically, Hueneme Canyon functioned as the eastern termination of the Santa Barbara littoral cell by trapping all eastward littoral drift, not only feeding the large Hueneme submarine fan but acting as the major conduit of sediment to the deep Santa Monica Basin; however, recent dredging programs needed to maintain Channel Islands Harbor and the Port of Hueneme have moved the nearshore sediment trapped by jetties and breakwaters to an area southeast of the Hueneme Canyon head. Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft sediment and isolated areas of rocky habitat that support kelp-forest communities nearshore and rocky-reef communities in deep water. The potential marine benthic habitat types mapped in the Hueneme Canyon and vicinity map area are related directly to the geomorphology and sedimentary processes that are the result of its Quaternary geologic history. The two basic megahabitats in the map area are Shelf (continental shelf) and Flank (continental slope). The flat seafloor of the continental shelf in the Hueneme Canyon and vicinity map area is dynamic, as indicated by mobile sand sheets and coarser grained scour depressions. The active Hueneme Canyon provides considerable relief to the continental shelf in the map area, and its irregular morphology of eroded walls, landslide scarps, and deposits and gullies provide promising habitat for groundfish, crabs, shrimp, and other marine benthic organisms. Most invertebrates observed in the map area during camera ground-truth field operations are found on the edge of Hueneme Canyon, which may be an important area of recruitment and retention to other invertebrates and fishes. The smaller, more subtle, nonactive headless canyons located primarily on the continental slope also offer relief that provides habitat for groundfish and other organisms.

California↗
USGS2021

The Sedimentary Geochemistry and Paleoenvironments Project

Geobiology explores how Earth's system has changed over the course of geologic history and how living organisms on this planet are impacted by or are indeed causing these changes. For decades, geologists, paleontologists, and geochemists have generated data to investigate these topics. Foundational efforts in sedimentary geochemistry utilized spreadsheets for data storage and analysis, suitable for several thousand samples, but not practical or scalable for larger, more complex datasets. As results have accumulated, researchers have increasingly gravitated toward larger compilations and statistical tools. New data frameworks have become necessary to handle larger sample sets and encourage more sophisticated or even standardized statistical analyses.

Geobiology↗
USGS2008

Precambrian basement structure map of the continental United States - An interpretation of geologic and aeromagnetic data

The Precambrian basement rocks of the continental United States are largely covered by younger sedimentary and volcanic rocks, and the availability of updated aeromagnetic data (NAMAG, 2002) provides a means to infer major regional basement structures and tie together the scattered, but locally abundant, geologic information. Precambrian basement structures in the continental United States have strongly influenced later Proterozoic and Phanerozoic tectonism within the continent, and there is a growing awareness of the utility of these structures in deciphering major younger tectonic and related episodes. Interest in the role of basement structures in the evolution of continents has been recently stimulated, particularly by publications of the Geological Society of London (Holdsworth and others, 1998; Holdsworth and others, 2001). These publications, as well as others, stress the importance of reactivation of basement structures in guiding the subsequent evolution of continents. Knowledge of basement structures is an important key to understanding the geology of continental interiors.

Scientific Investigations Map↗
USGS1988

Effects of three-dimensional velocity structure on the seismicity of the 1984 Morgan Hill, California, aftershock sequence

A three-dimensional velocity model for the area surrounding the 24 April 1984 Morgan Hill earthquake has been developed by simultaneously inverting local earthquake and refraction arrival-time data. This velocity model corresponds well to the surface geology of the region, predominantly showing a low-velocity region associated with the sedimentary sequence to the southwest of the Madrone Springs fault. This low-velocity sequence extends to a depth of approximately 5 km. Previously constructed geologic cross-sections for this region had suggested that these sediments extended to a depth of less than 2 km. Relocation of 2,179 hypocenters with the three-dimensional velocity model did not show great differences when compared to locations done with a one-dimensional velocity model with station corrections. In both cases, the Calaveras fault is steep but has a noticeable dip to the northeast and the seismicity does not intersect the surface along the trace of the Calaveras fault in the southern half of the rupture zone. The greatest differences between the two sets of locations was that the locations using the three-dimensional velocity model were deeper, and fewer earthquakes were located within the low-velocity region. The focal mechanisms were also determined for 946 earthquakes using both the one-dimensional and three-dimensional earth models. Both earth models yield similar focal mechanisms for these earthquakes.

California↗
USGS1964

Reconnaissance geochemistry of stream sediments from three areas near Juneau, Alaska

Results of a preliminary inquiry into background metal content of stream sediments near Juneau, Alaska, and whether this background is related to geologic terrane indicate that stream sediments derived chiefly from metamorphic rocks show significantly higher modal nickel, zinc, and arsenic than do sediments derived mainly from sedimentary or igneous rocks. Metal-content data that are closely related to areal geology will be required before systematic geochemical prospecting by stream-sediment sampling in southeast Alaska will be very effective.

Alaska↗
USGS2019

On the eruption age and provenance of the Old Crow tephra

Tephrochronology is used to correlate and reconstruct geographically disparate sedimentary records of changing environment, climate, and landscape throughout geologic time. Single tephra layers represent isochronous markers across broad regions, thus accurate and precise radiometric constraints on the timing of eruption are critical to their utility. The Old Crow tephra is found throughout eastern Beringia and represents the largest preserved Pleistocene ashfall event in the region. Despite its volume and significance as a stratigraphic marker, the provenance of this tephra is debated, and the interpreted eruption age of marine isotope stage (MIS) 5 at ∼125 ka has vacillated. To investigate provenance and eruption age, we develop a geochemical fingerprint for the Old Crow tephra via titanomagnetite geochemistry, and zircon crystallization/cooling age via coupled U/Pb, U/Th, and (U Th)/He zircon geochronology. Our results indicate that Old Crow oxides are geochemically distinct from the commonly assumed source-caldera system at the Emmons Lake Volcanic Center (ELVC). Zircon crystals from the Old Crow tephra range in age from Proterozoic to Pleistocene, with concordant zircon U/Pb, U/Th, and (U Th)/He dates on the youngest population of grains suggesting crystallization in their parent magma, and in turn eruption, at 202.9 ± 9.5 ka. We discuss strengths and shortcomings of our radiogenic datasets in light of this result and review the far-reaching implications of a change in Old Crow eruption age.

Alaska↗
USGS1999

Late Cenozoic stratigraphy and tephrochronology of the western Black Mountains piedmont, Death Valley, California: Implications for the tectonic development of Death Valley

Geologic mapping combined with the tephrochronology of spatially isolated sedimentary sections along the western Black Mountains piedmont adjacent the Death Valley fault zone (DVFZ) improves the late Cenozoic stratigraphy from relative age to correlated age. Pliocene tephra layers identified in Funeral Formation conglomerates at Artist Drive and Copper Canyon include a “Nomlaki-like” tephra bed (ca. 3.4 Ma), the tuffs of Mesquite Spring (3.1–3.3 Ma), and a tuff of the lower Glass Mountain family (1.86–1.92 Ma). We informally name the early(?) to middle Pleistocene Mormon Point formation1, which contains tephra layers correlated with the upper Glass Mountain/Bishop family of tephra layers (0.76–1.2 Ma), the Lava Creek B ash bed (ca. 0.66 Ma), and the Dibekulewe ash bed (ca. 0.51 Ma). Identification of these tephra layers indicates that the maximum age of the overlying and inset lacustrine gravel and alluvial fan deposits is 0.51 Ma. The correlated age stratigraphy indicates that the dextral-oblique DVFZ has stepped basinward at Mormon Point and Copper Canyon since the late Pliocene. In contrast, during that same time the DVFZ at Artist Drive has not stepped basinward, but developed into a graben. The age of faulting on the low-angle (~19°–40°) Mormon Point turtleback fault is bracketed between 0.76 and 0.18 Ma, and the overlying Mormon Point formation shows no evidence of tilting, indicating slip on the turtleback fault was at a low-angle. Early Quaternary slip on the low-angle turtleback fault conflicts with the present versions of the pure shear, rolling-hinge, and detachment/rift models for Death Valley extension. Early Quaternary slip is most compatible with turtleback faults as folded or warped detachment fault. We propose that the warping is thermally driven and related to the Black Mountains igneous complex.

California, Nevada↗
USGS1990

Map showing drill-hole depths, lithologic intercepts, and partial isopachs of basin fill in the Winnemucca 1 degree by 2 degrees quadrangle, Nevada

The purpose of this map is to aid in the mineral-resource assessment and exploration of covered host rocks by displaying and interpreting data that can be used to estimate the depth of basin fill in the Winnemucca 1° by 2° quadrangle, Nevada. Publicly available information used in making this map includes water, petroleum, and geothermal well data, gravity data and models, seismic profiles, and geologic and geomorphic reports. Wells logs used for this map of the Winnemucca quadrangle are from the following sources: (1) logs of more than 1,000 water wells reported to the State of Nevada Division of Water Resources, which are on file with them in Reno and at the with U.S. Geological Survey in Carson City, (2) 44 petroleum wells collected by the Nevada Bureau of Mines (Lintz, 1957; Schilling and Garside, 1968; Garside and Schilling, 1977, Garside and others, 1977; 1988), and (3) Two geothermal wells reported in Zoback (1979) and Flynn and others (1982). Data from isostatic residual and Bouguer gravity maps by Wagini (1985) contributed to the interpretation of basin configuration. Gravity models of Dixie Valley (Schaefer, 1982, and Speed, 1976) and Grass Valley (Grannell and Noble, 1977) and seismic profiles of Grass and Pine Valleys (Potter and others, 1987) helped refine basis interpretations in those areas. The geologic base map of Paleozoic and Mesozoic igneous and sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Cenozoic structures was simplified from Stewart and Carlson (1976b).

Nevada↗