Search USGS⌕ Search

Geology topics

Robert P. Dickerson

Publications and source records attributed to Robert P. Dickerson.

9 recordsLinked to original sources
USGS2004

Geologic map of south-central Yucca Mountain, Nye County, Nevada

New 1:6,000-scale geologic mapping in a 20-square-kilometer area near the south end of Yucca Mountain, Nevada, which is the proposed site of an underground repository for the storage of high-level radioactive wastes, substantially supplements the stratigraphic and structural data obtained from earlier, 1:24,000-scale mapping. Principal observations and interpretations resulting from the larger scale, more detailed nature of the recent investigation include: (1) the thickness of the Miocene Tiva Canyon Tuff decreases from north to south within the map area, and the lithophysal zones within the formation have a greater lateral variability than in areas farther north; and (2) fault relations are far more complex than shown on previous maps, with both major (block-bounding) and minor (intrablock) faults showing much lateral variation in (a) the number of splays and (b) the amount, distribution, and width of anastomosing breccia and fracture zones.

Nevada↗
USGS2002

Geologic map of the Yucca Mountain region, Nye County, Nevada

Yucca Mountain, Nye County, Nev., has been identified as a potential site for underground storage of high-level radioactive waste. This geologic map compilation, including all of Yucca Mountain and Crater Flat, most of the Calico Hills, western Jackass Flats, Little Skull Mountain, the Striped Hills, the Skeleton Hills, and the northeastern Amargosa Desert, portrays the geologic framework for a saturated-zone hydrologic flow model of the Yucca Mountain site. Key geologic features shown on the geologic map and accompanying cross sections include: (1) exposures of Proterozoic through Devonian strata inferred to have been deformed by regional thrust faulting and folding, in the Skeleton Hills, Striped Hills, and Amargosa Desert near Big Dune; (2) folded and thrust-faulted Devonian and Mississippian strata, unconformably overlain by Miocene tuffs and lavas and cut by complex Neogene fault patterns, in the Calico Hills; (3) the Claim Canyon caldera, a segment of which is exposed north of Yucca Mountain and Crater Flat; (4) thick densely welded to nonwelded ash-flow sheets of the Miocene southwest Nevada volcanic field exposed in normal-fault-bounded blocks at Yucca Mountain; (5) upper Tertiary and Quaternary basaltic cinder cones and lava flows in Crater Flat and at southernmost Yucca Mountain; and (6) broad basins covered by Quaternary and upper Tertiary surficial deposits in Jackass Flats, Crater Flat, and the northeastern Amargosa Desert, beneath which Neogene normal and strike-slip faults are inferred to be present on the basis of geophysical data and geologic map patterns. A regional thrust belt of late Paleozoic or Mesozoic age affected all pre-Tertiary rocks in the region; main thrust faults, not exposed in the map area, are interpreted to underlie the map area in an arcuate pattern, striking north, northeast, and east. The predominant vergence of thrust faults exposed elsewhere in the region, including the Belted Range and Specter Range thrusts, was to the east, southeast, and south. The vertical to overturned strata of the Striped Hills are hypothesized to result from successive stacking of three south-vergent thrust ramps, the lowest of which is the Specter Range thrust. The CP thrust is interpreted as a north-vergent backthrust that may have been roughly contemporaneous with the Belted Range and Specter Range thrusts. The southwest Nevada volcanic field consists predominantly of a series of silicic tuffs and lava flows ranging in age from 15 to 8 Ma. The map area is in the southwestern quadrant of the southwest Nevada volcanic field, just south of the Timber Mountain caldera complex. The Claim Canyon caldera, exposed in the northern part of the map area, contains thick deposits of the 12.7-Ma Tiva Canyon Tuff, along with widespread megabreccia deposits of similar age, and subordinate thick exposures of other 12.8- to 12.7-Ma Paintbrush Group rocks. An irregular, blocky fault array, which affects parts of the caldera and much of the nearby area, includes several large-displacement, steeply dipping faults that strike radially to the caldera and bound south-dipping blocks of volcanic rock. South and southeast of the Claim Canyon caldera, in the area that includes Yucca Mountain, the Neogene fault pattern is dominated by closely spaced, north-northwest- to north-northeast-striking normal faults that lie within a north-trending graben. This 20- to 25-km-wide graben includes Crater Flat, Yucca Mountain, and Fortymile Wash, and is bounded on the east by the 'gravity fault' and on the west by the Bare Mountain fault. Both of these faults separate Proterozoic and Paleozoic sedimentary rocks in their footwalls from Miocene volcanic rocks in their hanging walls. Stratigraphic and structural relations at Yucca Mountain demonstrate that block-bounding faults were active before and during eruption of the 12.8- to 12.7-Ma Paintbrush Group, and significant motion on these faults continued unt

IMAP↗
USGS2001

Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado

New 1:24,000-scale geologic mapping in the Colorado National Monument Quadrangle and adjacent areas, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of and data for the stratigraphy, structure, geologic hazards in the area from the Colorado River in Grand Valley onto the Uncompahgre Plateau. The plateau drops abruptly along northwest-trending structures toward the northeast 800 m to the Redlands area and the Colorado River in Grand Valley. In addition to common alluvial and colluvial deposits, surficial deposits include Holocene and late Pleistocene charcoal-bearing valley-fill deposits, late to middle Pleistocene river-gravel terrace deposits, Holocene to middle Pleistocene younger, intermediate, and old fan-alluvium deposits, late to middle Pleistocene local gravel deposits, Holocene to late Pleistocene rock-fall deposits, Holocene to middle Pleistocene young and old landslide deposits, Holocene to late Pleistocene sheetwash deposits and eolian deposits, and Holocene Cienga-type deposits. Only the lowest part of the Upper Cretaceous Mancos Shale is exposed in the map area near the Colorado River. The Upper and Lower? Cretaceous Dakota Formation and the Lower Cretaceous Burro Canyon Formation form resistant dipslopes in the Grand Valley and a prominent ridge on the plateau. Less resistant strata of the Upper Jurassic Morrison Formation consisting of the Brushy Basin, Salt Wash, and Tidwell Members form slopes on the plateau and low areas below the mountain front of the plateau. The Middle Jurassic Wanakah Formation nomenclature replaces the previously used Summerville Formation. Because an upper part of the Middle Jurassic Entrada Formation is not obviously correlated with strata found elsewhere, it is therefore not formally named; however, the lower rounded cliff former Slickrock Member is clearly present. The Lower Jurassic silica-cemented Kayenta Formation forms the cap rock for the Lower Jurassic carbonate-cemented Wingate Sandstone, which forms the impressive cliffs of the monument. The Upper Triassic Chinle Formation was deposited on the eroded and weathered Middle Proterozoic meta-igneous gneiss, pegmatite dikes, and migmatitic gneiss. Structurally the area is deceptively challenging. Nearly flat-lying strata on the plateau are folded by northwest-trending fault-propagation folds into at least two S-shaped folds along the mountain front of the plateau. Strata under Grand Valley dip at about 6 degrees to the northeast. In the absence of local evidence, the uplifted plateau is attributed to Laramide deformation by dated analogous structures elsewhere in the Colorado Plateau. The major exposed fault records high-angle reverse relationships in the basement rocks but dissipates strain as a triangular zone of distributed microfractures and cataclastic flow into overlying Mesozoic strata that absorb the fault strain, leaving only folds. Evidence for younger, probably late Pliocene or early Pleistocene, uplift does exist at the antecedent Unaweep Canyon south and east of the map area. To what degree this younger deformation affected the map area is unknown. Several geologic hazards affect the area. Middle and late Pleistocene landslides involving the smectite-bearing Brushy Basin Member of the Morrison Formation are extensive on the plateau and common in the Redlands below the plateau. Expansive clay in the Brushy Basin and other strata create foundation stability problems for roads and homes. Flash floods create a serious hazard to people on foot in narrow canyons in the monument and to homes close to water courses downstream from narrow restrictions close to the monument boundary.

Colorado↗
USGS1998

Bedrock geologic map of the Yucca Mountain area, Nye County, Nevada

Yucca Mountain, Nye County, Nevada, has been identified as a potential site for underground storage of high-level radioactive nuclear waste. Detailed bedrock geologic maps form an integral part of the site characterization program by providing the fundamental framework for research into the geologic hazards and hydrologic behavior of the mountain. This bedrock geologic map provides the geologic framework and structural setting for the area in and adjacent to the site of the potential repository. The study area comprises the northern and central parts of Yucca Mountain, located on the southern flank of the Timber Mountain-Oasis Valley caldera complex, which was the source for many of the volcanic units in the area. The Timber Mountain-Oasis Valley caldera complex is part of the Miocene southwestern Nevada volcanic field, which is within the Walker Lane belt. This tectonic belt is a northwest-striking megastructure lying between the more active Inyo-Mono and Basin-and-Range subsections of the southwestern Great Basin. Excluding Quaternary surficial deposits, the map area is underlain by Miocene volcanic rocks, principally ash-flow tuffs with lesser amounts of lava flows. These volcanic units include the Crater Flat Group, the Calico Hills Formation, the Paintbrush Group, and the Timber Mountain Group, as well as minor basaltic dikes. The tuffs and lava flows are predominantly rhyolite with lesser amounts of latite and range in age from 13.4 to 11.6 Ma. The 10-Ma basaltic dikes intruded along a few fault traces in the north-central part of the study area. Fault types in the area can be classified as block bounding, relay structures, strike slip, and intrablock. The block-bounding faults separate the 1- to 4-km-wide, east-dipping structural blocks and exhibit hundreds of meters of displacement. The relay structures are northwest-striking normal fault zones that kinematically link the block-bounding faults. The strike-slip faults are steep, northwest-striking dextral faults located in the northern part of Yucca Mountain. The intrablock faults are modest faults of limited offset (tens of meters) and trace length (less than 7 km) that accommodated intrablock deformation. The concept of structural domains provides a useful tool in delineating and describing variations in structural style. Domains are defined across the study area on the basis of the relative amount of internal faulting, style of deformation, and stratal dips. In general, there is a systematic north to south increase in extensional deformation as recorded in the amount of offset along the block-bounding faults as well as an increase in the intrablock faulting. The rocks in the map area had a protracted history of Tertiary extension. Rocks of the Paintbrush Group cover much of the area and obscure evidence for older tectonism. An earlier history of Tertiary extension can be inferred, however, because the Timber Mountain-Oasis Valley caldera complex lies within and cuts an older north-trending rift (the Kawich-Greenwater rift}. Evidence for deformation during eruption of the Paintbrush Group is locally present as growth structures. Post-Paintbrush Group, pre-Timber Mountain Group extension occurred along the block-bounding faults. The basal contact of the 11.6-Ma Rainier Mesa Tuff of the Timber Mountain Group provides a key time horizon throughout the area. Other workers have shown that west of the study area in northern Crater Flat the basal angular unconformity is as much as 20° between the Rainier Mesa and underlying Paintbrush Group rocks. In the westernmost part of the study area the unconformity is smaller (less than 10°), whereas in the central and eastern parts of the map area the contact is essentially conformable. In the central part of the map the Rainier Mesa Tuff laps over fault splays within the Solitario Canyon fault zone. However, displacement did occur on the block-bounding faults after deposition of the Rainier Mesa Tuff inasmuch as it is locally caught up in the hanging-wall deformation of the block-bounding faults. Therefore, the regional Tertiary to Recent extension was protracted, occurring prior to and after the eruption of the tuffs exposed at Yucca Mountain.

Nevada↗
USGS1981

Potential source for crushed granite aggregate in Heard County, Georgia

The production of crushed stone suitable for highway and general construction is a major industry in Georgia. The state ranks eighth in the nation in overall crushed stone production, and first in crushed granite production. Crushed stone production in Georgia in 1979 was 40,902,000 short tons worth $154,021,000 (D.H. White, Jr., US Bureau of Mines, personal commun., Aug. 1980). More than 3,000 people were employed by the crushed stone industry in Georgia during that year. Presently, the only active quarry in Heard County is located in an amphibolite. Amphibolite is not a conventional aggregate. It has a high specific gravity, a tendency to make elongate fragments, and varies considerably in abrasion tests. Because the nearest approved aggregate quarry is more than 25 miles from Franklin, the county seat, the purpose of this brief report is to describe a body of granite gneiss that may provide suitable aggregate for the crushed stone industry, potential quarry operators and various agencies in Heard County. This report is part of a project to study the geology and mineral resources of the Piedmont south of the Brevard Zone, and is not intended to supplant detailed site investigations by industry or consultants. The report is a joint effort between the Georgia Geologic Survey and the Office of Materials and Research of the Georgia Department of Transportation.

Georgia↗