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At least 1,207 records · Page 67Linked to original sources
USGS2026

Preliminary bedrock geologic map of the Port Henry quadrangle, Essex County, New York, and Addison County, Vermont

Introduction The bedrock geology of the 7.5-minute Port Henry quadrangle consists of deformed and metamorphosed Mesoproterozoic gneisses of the Adirondack Highlands unconformably overlain by weakly deformed lower Paleozoic sedimentary rocks of the Champlain Valley. The Mesoproterozoic rocks occur on the eastern edge of the Adirondack Highlands and represent an extension of the Grenville Province of Laurentia. Mesoproterozoic paragneiss, marble, and amphibolite hosted the emplacement of an anorthosite-mangerite-charnockite-granite (AMCG) suite, now exposed mostly as orthogneiss, at approximately 1.18–1.15 Ga (giga-annum). In the Port Henry quadrangle, the AMCG metaigneous rocks (Yhg, Ygb, Yanw) intruded older, mostly metasedimentary rocks of the Grenville Complex during the middle to late Shawinigan orogeny (~1,160–1,150 Ma [mega-annum]). All rocks were subsequently metamorphosed to upper amphibolite to granulite facies conditions during the 1,080–1,050 Ma Ottawan orogeny. New mapping reveals four periods of deformation: (1) D1 produced rarely preserved isoclinal folds in the paragneiss and marble and predates AMCG magmatism. (2) Subsequent D2 deformation produced the dominant gneissic fabric preserved in the rock, recumbent folding, and deformed all the Proterozoic units in the map area. Syn- to late-D2 felsic magmatism resulted in the regionally extensive Lyon Mountain Granite Gneiss, which hosts numerous magnetite ore bodies. (3) Mylonitic extensional shear zones and core complex formation marked the beginning of D3 deformation. Protracted D3 deformation resulted in F3 upright folding, dome and basin formation, pegmatite intrusion, reactivation of the S2 foliation, partial melting, metamorphism, metasomatism, iron-ore remobilization, and intrusion of magnetite-bearing pegmatite both as layer-parallel sills and crosscutting dikes. (4) D4 created northeast- and northwest-trending local high-grade ductile shear zones and boudinage, northwest-trending regional kilometer (km)-wide ductile shear zones, and crosscutting granitic pegmatite dikes. The development of the late-stage regional shear zones (D4) was likely due to the continuation of extensional doming and uplift from upper amphibolite facies conditions at the end of the Ottawan orogeny. The majority of iron-ore deposits in the Port Henry and adjacent Witherbee quadrangles are in the hanging wall of these extensional shear zones. In the Port Henry quadrangle, the km-wide Cheney Mountain shear zone is the result of D4 deformation. Kilometer-scale lineaments readily observed in lidar data are Ediacaran mafic dikes and Phanerozoic brittle faults. The Paleozoic rocks are part of the Early Cambrian to Late Ordovician carbonate bank on the ancient margin of Laurentia. The approximately 1-km-thick Cambrian to Ordovician stratigraphy records a transition from synrift clastics to passive-margin peritidal carbonate buildups to gradually deeper-water subtidal- to shelf-carbonates during foreland basin development associated with the Taconic orogeny. The Paleozoic rocks are weakly folded and block faulted. Large areas of the Champlain Valley are covered by undifferentiated glacial deposits, some of which contain mapped landslides. The map also shows waste rock piles and tailings from historical mining operations. This study was undertaken to improve our understanding of the bedrock geology in the Adirondack Highlands, establish a modern framework for 1:24,000-scale bedrock geologic mapping in the Adirondacks, provide a context for historical iron mines in the eastern Adirondacks, and update the stratigraphy of the Champlain Valley in New York and Vermont. This Open-File Report includes a bedrock geologic map; a description of map units; a correlation of map units; and a geographic information system database that includes bedrock geologic units, faults, outcrops, and structural geologic information.

New York, Vermont↗
USGS2002

Geologic Map of the Diana Chasma Quadrangle (V-37), Venus

Introduction The Diana Chasma quadrangle (V-37), an equatorial region between 0° to 25° S. and 150° to 180° E. that encompasses ~8,400,000 km 2 , is broadly divided into southern Rusalka Planitia in the north, eastern Aphrodite Terra in the central region, and unnamed regions to the south. Geologic mapping constrains the temporal and spatial relations of the major features, which include a tessera inlier, Markham crater, six large coronae (300-675 km diameter), four smaller coronae (150-225 km diameter), Diana and Dali chasmata, a large fracture zone, and southern Rusalka Planitia. Eastern Aphrodite Terra, marked here by large coronae, deep chasmata, and an extensive northeast-trending fracture zone, extends from Atla Regio to Thetis Regio. The large coronae are part of a chain of such features that includes Inari Corona to the west-southwest and Zemina Corona to the northeast. V-37 quadrangle is bounded on the north by Rusalka Planitia and on the south by Zhibek Planitia. International Astronomical Union (IAU) approved and provisional nomenclature and positions for geographic features within Diana Chasma quadrangle are shown on the geologic map. [Note: Atahensik Corona was referred to as Latona Corona in much previously published literature.] Diana Chasma quadrangle hosts some of the steepest topography on Venus. Altimetry measurements range from -2.5 to 4.7 km (0.0 = mean planetary radius), with a surface mean of 0.6 km. Fractures and faults within the central fracture/rift zone create large blocks of down-dropped material, especially along the east-central edge of the map area. The Dali and Diana chasmata display slopes of >30°, the steepest and deepest trenches on Venus. Both chasmata host landslide deposits presumably sourced from the steep chasmata walls. The tessera inlier, coronae, and ridge belts sit topographically above Rusalka and Zhibek planitiae. Rusalka Planitia topography describes broad undulations having northwest-trending ridges spaced ~200 km apart. The most distinctive ridge, Vetsorgo Dorsum, centered at 6.5° S., 163° E., is a Class I ridge belt owing to its simple arch morphology. The central interior of Markham crater sits topographically lower than the surrounding region, which slopes downward to the east.

IMAP↗
USGS1952

Geology and hydrology of dam sites on the island of St. Croix, Virgin Islands

The Virgin Islands Corporation plans to build a series of small earth dams along some of the streams on the island of St. Croix, and field studies involving the selection and hydrology of possible sites was carried on by the Geological Survey during the months of August and September 1951. The island of St. Croix is the largest of the three principal islands of the Virgin. Islands group owned by the United States. It is about 21 miles long and 6 miles wide near the center and has an area of about 84 square miles. The northwestern part of the island contains mountains that reach a maximum altitude of 1,165 feet; the eastern half of the island is submountainous, containing some hills 600 to 800 feet in altitude. A coastal lowland area containing a few east-west trending marl and limestone hills characterizes the southwestern part of the island. The streams in the east half of the island and along the northwest coast are relatively short and are dry during most of the year. The streams draining the mountains from the south cross the coastal lowland in narrow and shallow ditches. The southeastward drainage from the eastern part of the mountainous area is diverted by Salt River and enters the sea on the north coast of the island. In the headwaters of some streams there is a small flow of water during most of the year that disappears below the surface upstream from or near the foot of the mountains. During most of the year the streams are essentially dry, flowing only after periods of heavy rainfall. In the coastal lowland near Bethlehem the average annual rainfall is about 46 inches. The east end of the island is relatively dry and the precipitation is estimated to be approximately 20 inches annually; the northwestern end of the island receives the most rainfall, probably more than 50 inches annually. Records show that from 1861 to 1876 there was deficient rainfall and the accumulated departure below normal was about 56 inches (fig. 2). From 1876 to 1920 there were numerous years of above -normal precipitation and the departure curve rose nearly 100 inches, to more than 40 inches above normal. From 1936 to 1950 there has been a more or less continuous decline in rainfall, amounting to a net deficiency of 72 inches, or from 44 inches above to 28 inches below normal. These changes in rainfall have a direct effect on the volume of stream flow an island. There are two general rock types on the island. The Mount Eagle volcanics and the intruded diorite are hard, dense crystalline rocks; the rock's underlying the coastal lowland and belt of hills between Salt River and Christiansted are sedimentary rocks, such as marl, limestone, sand, gravel, and clay. The permeability of the crystalline rocks and of the gray clay and basal conglomerate of the Jealousy formation is low and they are water bearing in few places. The Kingshill formation is composed of light-gray clay and light-yellow marl and included beds of limestone. In places the limestone contains solutional openings that yield water to wells. The alluvial sand, gravel, and clay that unconformably overlie the Kingshill marl include permeable beds that yield relatively large quantities of water to wells in a few places. It is evident from the small stream flow that by far the greatest part of the 46-inch average annual precipitation on the island is returned to the atmosphere through evaporation and transpiration. There are no records of stream flaw or ground-water flow from the drainage basins, but it is estimated that in some years the amount of water lost through evaporation and transpiration may be more than 90 percent of the total water available. It is proposed that a program be started and continued to collect and evaluate data on the hydrology of the island. The purpose of the dam-building program is to retain on the land a part of the water that formerly flowed to the sea and was of no beneficial use. Owing to the lack of hydrologic data, the maximum number of dams needed is not known; consequently, practically all possible sites on publicly owned land and sites that would benefit those lands were studied. Thus, 3 sites were selected in the valley near Little Grange that is a source of supply to the public-supply well field of Frederiksted; 19 sites were selected on or near property owned by the Virgin Islands Corporation; and 4 sites were selected along the Salt River above the public-supply well field of Christiansted. During most of the year the water table is at or below the beds of the streams; consequently, if permeable rocks underlie a pond or dam it is possible that there may be leakage from the pond to the water table. In general, leakage from dam sites underlain by crystalline rocks of the fount Eagle volcanics or clay of the Kingshill marl will be negligible, but leakage from sites underlain by limestone in the Kingshill marl or sand and gravel of the alluvium may be great. Potential leakage at each site selected is discussed.

Virgin Islands↗
USGS2009

The Longview/Lakeview barite deposits, southern National Petroleum Reserve, Alaska (NPRA) — Potential-field models and preliminary size estimates

Longview and Lakeview are two of the larger stratiform barite deposits hosted in Mississippian Akmalik Chert in the Cutaway Basin area (Howard Pass C-3 quadrangle) of the southern National Petroleum Reserve, Alaska (NPRA). Geologic studies for the South NPRA Integrated Activity Plan and Environmental Impact Statement process included an attempt to evaluate the possible size of barite resources at Longview and Lakeview by using potential-field geophysical methods (gravity and magnetics). Gravity data from 227 new stations measured by the U.S. Geological Survey, sparse regional gravity data, and new, high-resolution aeromagnetic data were forward modeled simultaneously along seven profiles perpendicular to strike and two profiles along strike of the Longview and Lakeview deposits. These models indicate details of the size and shape of the barite deposits and suggest thicknesses of 15 to 24 m, and 9 to 24 m for the Longview and Lakeview deposits, respectively. Two groups of outcrops span 1.8 km of strike length and are likely connected below the surface by barite as much as 10 m thick. Barite of significant thickness (>-5 m) is unlikely to occur north of the presently known exposures of the Longview deposit. The barite bodies have irregular (nonplanar) bases suggestive of folding; northwest-trending structures of small apparent offset cross strike at several locations. Dip of the barite is 10 to 25 degrees to the southeast. True width of the bodies (the least certain dimension) is estimated to be 160 to 200 m for Longview and 220 to 260 m for Lakeview. The two bodies contain a minimum of 4.5 million metric tons of barite and more than 38 million metric tons are possible. Grades of the barite are relatively high, with high specific gravities and low impurities. The potential for the Cutaway Basin to host economically minable quantities of barite is uncertain. Heavy-mineral concentrate samples from streams in the area, trace-element analyses, and physicalproperty measurements of bulk samples derived from trenching or drilling would be valuable for future assessment work.

Alaska↗
USGS2022

Attribution of monotonic trends and change points in peak streamflow across the conterminous United States using a multiple working hypotheses framework, 1941–2015 and 1966–2015

The U.S. Geological Survey has a long history of leading flood-frequency analysis studies. These studies play a critical role in the assessment of risk, protection of lives, and planning and design of flood protection infrastructure. Standard flood-frequency analysis is based on the assumption of stationarity—that is, that the distribution of floods at a given site varies around a particular mean within a particular envelope of variance (and skew) and that these parameters of the underlying statistical distribution representative of the floods do not vary over time. Gradual or abrupt changes in one or more of the distributional parameters are called nonstationarities and violate the underlying assumptions of current U.S. Federal Government guidelines for flood-frequency analysis. Uncertainty exists as to what degree of violations calls for the use of a modified method for flood-frequency analysis and what the modified method(s) should be. When deciding whether to perform nonstationary flood-frequency analysis and choosing a method for such analysis, it is important to understand the causes of the nonstationarity. Gradual or abrupt changes in distributional properties of floods may be the result of numerous factors, such as regulation, diversion, land-use change, or climate change. In the interest of developing a cohesive national approach for better understanding the causes of nonstationarities and incorporating potential or observed changes into flood-frequency estimates, subject-matter experts from the U.S. Geological Survey and cooperators worked together to develop a multiple working hypotheses framework for making attributions and a common vocabulary for making provisions of confidence. Seven regional teams of these experts used ancillary datasets and institutional knowledge to evaluate plausible causes for monotonic trends and change points in annual peak-streamflow data for the conterminous United States that had been identified in an earlier phase of the project. The first chapter of this professional paper describes the development of a list of the potential attributions, presents a literature review of the potential attributions, describes the regional approach, summarizes insights obtained from the attribution process, and suggests future research. The other chapters provide the methods used for attribution in the seven regions—Pacific Northwest, Upper Plains, Midwest, Northeast, Southwest, South-Central, and Southeast—and summarize the regional patterns of nonstationarities.

Conterminous United States↗
USGS2010

Thermal Imaging of the Waccasassa Bay Preserve: Image Acquisition and Processing

Thermal infrared (TIR) imagery was acquired along coastal Levy County, Florida, in March 2009 with the goal of identifying groundwater-discharge locations in Waccasassa Bay Preserve State Park (WBPSP). Groundwater discharge is thermally distinct in winter when Floridan aquifer temperature, 71-72 degrees F, contrasts with the surrounding cold surface waters. Calibrated imagery was analyzed to assess temperature anomalies and related thermal traces. The influence of warm Gulf water and image artifacts on small features was successfully constrained by image evaluation in three separate zones: Creeks, Bay, and Gulf. Four levels of significant water-temperature anomalies were identified, and 488 sites of interest were mapped. Among the sites identified, at least 80 were determined to be associated with image artifacts and human activity, such as excavation pits and the Florida Barge Canal. Sites of interest were evaluated for geographic concentration and isolation. High site densities, indicating interconnectivity and prevailing flow, were located at Corrigan Reef, No. 4 Channel, Winzy Creek, Cow Creek, Withlacoochee River, and at excavation sites. In other areas, low to moderate site density indicates the presence of independent vents and unique flow paths. A directional distribution assessment of natural seep features produced a northwest trend closely matching the strike direction of regional faults. Naturally occurring seeps were located in karst ponds and tidal creeks, and several submerged sites were detected in Waccasassa River and Bay, representing the first documentation of submarine vents in the Waccasassa region. Drought conditions throughout the region placed constraints on positive feature identification. Low discharge or displacement by landward movement of saltwater may have reduced or reversed flow during this season. Approximately two-thirds of seep locations in the overlap between 2009 and 2005 TIR night imagery were positively re-identified in 2009. These results indicate a 33 percent chance of feature omission in the 2009 imagery. This assessment of seep location and distribution contributes to an understanding of the underlying geology, the role of fault and fracture patterns, and the presence of both interconnected and constrained flow paths in the region. The maps and evaluations will enhance Park management efforts, interpretation of Park resources, and increase understanding of the combined effects of land and water use on the coastal lowlands, estuarine habitats, and natural resources of WBPSP.

Open-File Report↗
USGS2006

Geologic map of the Valle 30' x 60' quadrangle, Coconino County, northern Arizona

The geologic map of the Valle 30' x 60' quadrangle is the result of a cooperative effort between the U.S. Geological Survey and the National Park Service to provide geologic information for regional resource management and visitor information services for Grand Canyon National Park, Arizona. The map area encompasses approximately 1,960 sq.mi. within Coconino County, northern Arizona and is bounded by long 112 deg to 113 deg W. and lat 35 deg 30 min to 36 deg N. and lies within the southern Colorado Plateaus geologic province (herein Colorado Plateau). The map area is locally subdivided into four physiographic parts; (1) the Grand Canyon (Cataract Canyon and extreme northeast corner of the map area), (2) the Coconino Plateau, (3) the Mount Floyd Volcanic Field, and (4) the San Francisco Volcanic Field as defined by Billingsley and others, 1997. Elevations range from 7,460 ft (2,274 m) on the Coconino Plateau along State Highway 64 northeast corner of the map area, to about 4,200 ft (1,280 m) at the bottom of Cataract Canyon. Settlements within the map area include Tusayan and Valle, Arizona. State Highway 64 and U.S. Highway 180 provide access to the Tusayan and Valle areas. Indian Route 18 is a paved highway in the northwest corner of the map area that is maintained by the Hualapai and Havasupai Indian Tribes and leads from State Route 66 about 7 mi (11 km) east of Peach Springs, Arizona to Hualapai Hilltop, a parking lot just north of the map area at the rim of Cataract Canyon where visitors begin an 8 mi (13 km) hike into Havasupai, Arizona. Other remote parts of the map are accessed by two dirt roads, which are maintained by Coconino County, and by several unmaintained local ranch roads. Weather conditions restrict travel within the area and visitors must obtain permission to access a few local ranch lands in the south-central edge of the map area. Extra water and food are highly recommended when traveling in this remote region. Access into Cataract Canyon is restricted to horse or foot travel and visitors must obtain permission from the Havasupai Tribe to hike within the Havasupai Indian Reservation. In the central part of the map area, most of the land is privately owned and managed by the Babbitt Ranches Inc. in conjunction with the Nature Conservancy and the Navajo Tribe. In the southern half of the map, land alternates between privately owned land and State land forming a checkerboard pattern. The National Park Service manages land in Grand Canyon National Park (extreme northeast edge of map area), the U.S. Forest Service manages lands in the Kaibab National Forest, the Hualapai Tribe manages lands in the northwest quarter of the map area, and the Havasupai Tribe manages lands within Cataract Canyon and adjacent parts of the Coconino Plateau.

Scientific Investigations Map↗
USGS1986

Catastrophic flooding and eruption of ash-flow tuff at Medicine Lake volcano, California

Catastrophic flooding has eroded a discontinuous network of oversized anastomosing channels on the northwest flank of the Medicine Lake volcano. Most of these previously unrecognized channels were cut into an andesitic ash-flow tuff; boulders as large as 2 m in intermediate diameter were moved in terrain where little rain falls today and stream erosion is nonexistent or minimal. The flooding was probably triggered by eruption of andesite tuff through a late Pleistocene ice cap on the volcano, about 60,000 to 70,000 or about 130,000 B.P.

Geology↗
USGS1992

Evidence from Cd/Ca ratios in foraminifera for greater upwelling off California 4,000 years ago

UPWELLING of nutrient-rich Pacific deep water along the North American west coast is ultimately driven by the temperature difference between air masses over land and over the ocean. The intensity of upwelling, and biological production in the region, could therefore be affected by anthropogenic climate change. Examination of the geological record is one way to study the link between climate and upwelling. Because Pacific deep water is enriched in cadmium, dissolved cadmium concentrations in coastal water off central California reflect the intensity of upwelling. By demonstrating that the Cd/Ca ratio in the shell of a benthic foraminifer, Elphidiella hannai, is proportional to the Cd concentration in coastal water, we show here that foraminiferal Cd/Ca ratios can be used to detect past changes in mean upwelling intensity. Examination of a sediment core from the mouth of San Francisco Bay reveals that foraminiferal Cd/Ca decreased by about 30% from 4,000 years ago to the present, probably because of a reduction in coastal upwelling. This observation is consistent with predictions of atmospheric general circulation models that northwesterly winds, which drive upwelling, became weaker over this period as summer insolation of the Northern Hemisphere decreased.

Nature↗
USGS2015

California State Waters Map Series: Offshore of Refugio Beach, 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 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 Offshore of Refugio Beach map lies within the western Santa Barbara Channel region of the Southern California Bight. 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 is in the southern 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 province, and geodetic studies indicate that the region is presently undergoing north-south shortening. Uplift rates (as much as 0.5 mm/yr) that are based on studies of onland marine terraces provide further evidence of significant shortening. The coastal zone of this map area lies at the steep flank of the Santa Ynez Mountains. The crest of the range, which lies about 8 km from the shoreline (north of the map area), has a maximum elevation of about 780 m. This area is largely open space, partly used for livestock grazing, with no significant towns or population centers. Highway 101 crosses the map area, adjacent to and within a few hundred meters of the shoreline. The most significant developments are the recreational state beaches at El Capitan Beach and Refugio Beach. The beaches are subject to erosion each winter during storm-wave attack, and then they undergo gradual recovery or accretion during the more gentle wave climate of the late spring, summer, and fall months. The Offshore of Refugio Beach map area lies in the west-central part of the Santa Barbara littoral cell, which is characterized by west-to-east transport of sediment from Point Arguello on the northwest to Hueneme and Mugu Canyons on the southeast. Longshore drift rates have been reported to range from about 160,000 to 800,000 tons/yr, averaging 400,000 tons/yr. Sediment supply to the western and central part of the littoral cell, including the map area, is mainly from relatively small coastal watersheds. Within the map area, these coastal watersheds include (from east to west) Cañada del Capitan, Tajiquas Creek, Arroyo Hondo, Cañada del Molino, and several unnamed canyons and creeks. The Santa Ynez and Santa Maria Rivers, the mouths of which are 80 to 120 km northwest of the map area, are not considered significant sediment sources because Point Conception and Point Arguello provide obstacles to downcoast sediment transport and also because much of their sediment load is trapped in dams. The Ventura and Santa Clara Rivers, the mouths of which are about 70 km to the southeast of the map area, are not sediment sources for the map area. The offshore part of the map area consists of relatively flat and shallow continental shelf, which dips gently seaward (about 0.8° to 1.0°) so that water depths at the shelf break, roughly coincident with the California’s State Waters limit, are about 80 to 100 m. This part of the Santa Barbara Channel is relatively well protected from large Pacific swells from the north and northwest by Point Conception and from the south and southwest by offshore islands and banks. The shelf is underlain by variable amounts of upper Quaternary marine and fluvial sediments deposited as sea level fluctuated in the late Pleistocene. In the map area, the shelf break is at depths of about 90 m and lies about 5.6 to 6.4 km offshore. Beyond the shelf break, the slope is steep (as much as about 7°) and unstable. Several submarine landslides, including the large (130 km 2 ) Goleta landslide complex, have been documented offshore of Goleta, a few kilometers east of the map area. This compound slump complex may have been initiated more than 200,000 year ago, but it also includes three recent failures that may have been generated 8,000 to 10,000 years ago. A local, 10-m-high tsunami may have been generated from these failure events. Small folds related to local faulting are superimposed on the homocline that makes up the south flank of the Santa Ynez Mountains. One of these superimposed anticlines hosts the Molino gas field, which was discovered in 1962 and subsequently developed through directional drilling from onshore wells. The Oligocene Sespe and Vaqueros Formations are the reservoirs in the Molino gas field, and the map area includes numerous seafloor hydrocarbon seeps. Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with 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 Offshore of Refugio Beach map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats, which lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats, primarily are composed of soft sediment interrupted by a few carbonate mounds. This homogeneous seafloor of sediment and low-relief bedrock provides promising habitat for groundfish, crabs, shrimp, and other marine benthic organisms.

California↗
USGS1972

Reconnaissance geology of the Precambrian rocks in the Bi'r Ghamrah quadrangle, Kingdom of Saudi Arabia

Three sequences of volcanic and sedimentary rocks are identified in the Precambrian rocks of the Bi'r Ghamrah quadrangle at the eastern edge of the Precambrian Shield in central Saudi Arabia. The oldest sequence is called the Bi'r Khountina Group. It consists of conglomerate marble, andesite, and graywacke. Unconformably overlying this group is a sequence of graywacke with minor lava called the Murdama Group. In a small area in the southern part of the quadrangle, these rocks are unconformably overlain by rhyolitic tuff and rhyolite tentatively correlated with the Shammar Rhyolite. The older of these sedimentary and volcanic rocks were intruded by diorite and gabbro and by a large pluton of alkalic granite. A contact metamorphic aureole was formed in the Bi'r Khountina and Murdama Groups adjacent to the granite, and feeder dikes of the Sbmmmar Rhyolite(?) intrude the granite. The Bi'r Khountina Group is folded into a south-plunging asymmetrical anticlinorium, the west limb of which is repeated across northwest-trending faults. The Murdama Group appears to have been folded along the same axes, but the contact aureole against the alkalic granite and the imprint of the west-northwest striking Najd fault zone cause the rocks of the Murdama Group to appear to trend westward. Results of spectrographic and chemical analyses of wadi sand, heavy-mineral concentrates, and detrital magnetite show small anomalies. The ultramafic rocks intruded prior to the deposition of the Murdama Group are the source of anomalous chromium and lanthanum and of threshold nickel, scandium, and vanadium. The intrusive rocks younger than the Murdama Group are sources for anomalous lead and threshold silver, boron, barium, beryllium, zirconium, lanthanum, and tin. One small ancient working, probably opened for gold, is present, and at least four places in the Precambrian part of the quadrangle ere potentially favorable for gold, silver, and lead. Chromite is a potential resource in the northeastern part of the quadrangle.

Open-File Report↗
USGS1988

Geology of an area near Brentwood, Williamson County, Tennessee

The lithology and geologic structure of an area near Brentwood, Williamson County, Tennessee, were studied to define the potential aquifers and confining units of the ground-water flow system. Four formations were identified. They are, in descending order, the Bigby-Cannon Limestone, the Hermitage Formation, the Carters Limestone, and the Lebanon Limestone. The Bigby-Cannon Limestone and the Carters Limestone are potential aquifers. The Hermitage Formation and the Lebanon Limestone are confining units. The Bigby-Cannon Limestone and the Hermitage Formation have been affected by recent erosion. Any variation of the Carters Limestone is controlled by pre-Carters erosion of the top of the Lebanon Limestone. The thickness of the Carters Limestone ranges from 65 to 79 feet. Structurally, the area reflects the regional northwest dip. A small scale anti-cline-syncline pair also is evident. This feature is not a result of erosion and also occurs in the T-3 bentonite bed in the Carters Limestone.

Tennessee↗
USGS1981

Geochemical survey of Shining Rock Wilderness, Heywood County, North Carolina

The U.S. Geological Survey (USGS) made a reconnaissance geochemical survey of the Shining Rock Wilderness (fig. 1) to test for unidentified or unexposed mineral deposits that might be recognized by their geochemical halos. Similar geochemical survey based on trace-element analyses have been credited with the discovery of many types of mineral deposits (Hawkes and Webb, 1962). Although no metallic mineral deposits are known in the study area, the same sequence of rocks that is exposed there contains small deposits of copper-bearing sulfides 10-18 mi (16-28 km) west and southwest of the wilderness (Gair and Slack, 1979). Keith (1907, p. 8) reports minor amounts of copper sulfides and iron sulfides in schist and in quartz veins cutting schist near Retreat, 4 mi (6.5 km) northwest of the wilderness. An old gold mine, the Boylston mine, on Forge Mountain 10 mi (16 km) east of the wilderness (Nitze and Hanna, 1896, p. 181-191) is in metasedimentary rocks of the Great Smoky Group (Hadley and Nelson, 1971) which are probably younger than the rocks exposed in the wilderness.

North Carolina↗
USGS2008

Hydrogeologic Setting, Ground-Water Flow, and Ground-Water Quality at the Langtree Peninsula Research Station, Iredell County, North Carolina, 2000-2005

A 6-year intensive field study (2000-2005) of a complex, regolith-fractured bedrock ground-water system was conducted at the Langtree Peninsula research station on the Davidson College Lake Campus in Iredell County, North Carolina. This research station was constructed as part of the Piedmont and Mountains Resource Evaluation Program, a cooperative study being conducted by the North Carolina Department of Environment and Natural Resources and the U.S. Geological Survey. Results of the study characterize the distinction and interaction of a two-component ground-water system in a quartz diorite rock type. The Langtree Peninsula research station includes 17 monitoring wells and 12 piezometers, including 2 well transects along high to low topographic settings, drilled into separate parts of the ground-water-flow system. The location of the research station is representative of a metaigneous intermediate (composition) regional hydrogeologic unit. The primary rock type is mafic quartz diorite that has steeply dipping foliation. Primary and secondary foliations are present in the quartz diorite at the site, and both have an average strike of about N. 12 degree E. and dip about 60 degree in opposite directions to the southeast (primary) and the northwest (secondary). This rock is cut by granitic dikes (intrusions) ranging in thickness from 2 to 50 feet and having an average strike of N. 20 degree W. and an average dip of 66 degree to the southwest. Depth to consolidated bedrock is considered moderate to deep, ranging from about 24 to 76 feet below land surface. The transition zone was delineated and described in each corehole near the well clusters but had a highly variable thickness ranging from about 1 to 20 feet. Thickness of the regolith (23 to 68 feet) and the transition zone do not appear to be related to topographic setting. Delineated bedrock fractures are dominantly low angle (possibly stress relief), which were observed to be open to partially open at depths of as much as 479 feet below land surface. Well yields ranged from about 3 to 50 gallons per minute. The connection of fracture zones at depth was demonstrated in three bedrock wells during a 48-hour aquifer test, and drawdown curves were similar for all three wells. General findings of this study help characterize ground-water flow in the Piedmont and Mountains ground-water systems. Ground-water flow generally is from high to low topographic settings. Ground-water flow discharges toward a surface-water boundary (Lake Norman), and vertical hydraulic gradients generally are downward in recharge areas and upward in discharge areas. Dominant water types are calcium-bicarbonate and are similar in all three zones (regolith, transition zone, and bedrock) of the ground-water system. Results of continuous ground-water-quality monitoring indicate that ground-water recharge may occur seasonally over a period of several months or after heavy rainfall periods over a shorter period of a few to several weeks.

North Carolina↗
USGS1953

Carnotite resources of the Dolores bench, Montrose County, Colorado

The Dolores bench is about 2 miles northwest of Uravan, Montrose County, Colo. From 1913 to November 1952 about 95,000 short tons of ore averaging 0.40 percent U 3 O 8 and 2.0 percent V 2 O 5 was mined from the Dolores bench. The production represents three periods of activity--1913-18, 1938-43, and 1948-52. The ore deposits are in broad sandstone lenses near the top of the Salt Wash member of the Jurassic Morrison formation. The deposits are mainly impregnations of sandstone by carnotite and vanadiferous clay minerals. The deposits are irregular tabular layers which occasionally include pod-like masses called “rolls”. The rolls as well as the mineralized areas enclosing them have a poorly defined northeast trend. Between December 4, 1951, and August 1, 1952, the U.S. Geological Survey diamond-drilled 183 holes totaling 53,654 feet. The indicated and inferred reserves of carnotite-bearing material, and the pounds of contained U 3 O 8 and V 2 O 5 area summarized in table 1. At the highest thickness and grade cutoffs (1 foot thick and 0.10 percent U 3 O 8 or 1.0 percent V 2 O 5 ), indicated and inferred ore reserves total 90,000 short tons, averaging 0.33 percent U 3 O 8 and 2.11 percent V 2 O 5 . These reserves include only those discovered by U.S. Geological Survey drilling. Potential reserves, whose existence is based on geologic evidence alone, are estimated to be about 10,000 short tons, averaging about 0.30 percent U 3 O 8 and 2.00 percent V 2 O 5 . No additional exploration of the Dolores bench is planned by the Geological Survey. Diamond drilling by claim owners is recommended in several parts of the area.

Colorado↗
USGS2003

The early Mesozoic Birdsboro central Atlantic margin basin in the Mid-Atlantic region, eastern United States

The early Mesozoic Birdsboro basin (new name) was a single, elongate depositional trough in the present Mid-Atlantic area of the eastern United States, extending north-eastward from central Virginia across Maryland, Pennsylvania, and New Jersey into southern New York. What now remains after erosion comprises the Barboursville, Culpeper, Gettysburg, and Newark remnants. Some 7?? km of late Triassic and early Jurassic continental sediments of varying provenances entered and spread across in the Birdsboro basin in several depositional environments. The five resulting sedimentary lithosomes include feldspathic sandstone, quartzose sandstone, red silty mudstone, gray shale, and fanglomerate. The extensive interbedding, intertonguing, and lateral gradation among these lithosomes suggest that they were contemporary and closely interrelated. The feldspathic sandstone lithosome contains sediment with a southeastern provenance that accumulated in a bajada environment extending the length of the southeastern side of the basin. Sediment in the quartzose sandstone lithosome had a northwestern provenance-the coarse-grained fraction formed regional alluvial fans at the mouths of four major input centers. The finer-grained fraction was deposited in the distal reaches of these fans and in the playa environments in the interfan areas; this fraction formed the red silty mudstone lithosome. Gray/black shales and argillites of the gray shale lithosome accumulated in lacustrine environments in the interfan areas. The fanglomerate lithosome comprises numerous small, lobate deposits of poorly sorted sediment along both basin margins. The location and time of activity of the northwest input centers largely determined the distribution and areal extent of the various depositional environments and consequent lithosome along the length and across the width of the basin. The Birdsboro basin was deformed (tilted, faulted, and folded) sometime after the deposition of the youngest preserved rocks (early Sinemurian). The deformation varied along the length of the basin, producing differences in the amount of tilting, structural elevation, and subsequent erosion. The present erosional remnants create the illusion of four originally separate depositional basins.

Geological Society of America Bulletin↗
USGS1986

Geochemical map of the North Fork John Day River Roadless Area, Grant County, Oregon

The Wilderness Act (Public Law 88-577, September 3, 1964) and related acts require the U.S. Geological Survey and the U.S. Bureau of Mines to survey certain areas on Federal lands to determine their mineral resource potential. Results must be made available to the public and submitted to the President and the Congress. This report presents the analytical results of a geochemical survey of the North Fork John Day River Roadless Area (B6253) in the Umatilla and Wallowa-Whitman National Forests, Grant County, Oregon. The North Fork John Day River Roadless Area was classified as a further planning area during the Second Roadless Area Review and Evaluation (RARE II) by the U.S. Forest Service, January 1979. The North Fork John Day River Roadless Area comprised 21,210 acres in the Umatilla and Wallowa-Whitman National Forests, Grant County, Oregon, about 30 miles northwest of Baker, Oregon. The irregularly shaped area extends for about 1 mile on both sides of a 25-mile segment of the North Fork John Day River from Big Creek on the west to North Fork John Day Campground on the east. Most of the roadless area is in the northern half of the Desolation Butte 15-minute quadrangle. The eastern end of the area is in parts of the Granite and Trout Meadows 7½-minute quadrangles.

Oregon↗
USGS2017

Modified mercalli intensities for nine earthquakes in central and western Washington between 1989 and 1999

We determine Modified Mercalli (Seismic) Intensities (MMI) for nine onshore earthquakes of magnitude 4.5 and larger that occurred in central and western Washington between 1989 and 1999, on the basis of effects reported in postal questionnaires, the press, and professional collaborators. The earthquakes studied include four earthquakes of M 5 and larger: the M 5.0 Deming earthquake of April 13, 1990, the M 5.0 Point Robinson earthquake of January 29, 1995, the M 5.4 Duvall earthquake of May 3, 1996, and the M 5.8 Satsop earthquake of July 3, 1999. The MMI are assigned using data and procedures that evolved at the U.S. Geological Survey (USGS) and its Department of Commerce predecessors and that were used to assign MMI to felt earthquakes occurring in the United States between 1931 and 1986. We refer to the MMI assigned in this report as traditional MMI, because they are based on responses to postal questionnaires and on newspaper reports, and to distinguish them from MMI calculated from data contributed by the public by way of the internet. Maximum traditional MMI documented for the M 5 and larger earthquakes are VII for the 1990 Deming earthquake, V for the 1995 Point Robinson earthquake, VI for the 1996 Duvall earthquake, and VII for the 1999 Satsop earthquake; the five other earthquakes were variously assigned maximum intensities of IV, V, or VI. Starting in 1995, the Pacific Northwest Seismic Network (PNSN) published MMI maps for four of the studied earthquakes, based on macroseismic observations submitted by the public by way of the internet. With the availability now of the traditional USGS MMI interpreted for all the sites from which USGS postal questionnaires were returned, the four Washington earthquakes join a rather small group of earthquakes for which both traditional USGS MMI and some type of internet-based MMI have been assigned. The values and distributions of the traditional MMI are broadly similar to the internet-based PNSN intensities; we discuss some differences in detail that reflect differences in data-sampling procedure, differences in the procedure used to assign intensity numbers from macroseismic observations, and differences in how intensities are mapped.

Oregon, Washington↗