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At least 667 records · Page 37Linked to original sources
USGS2016

Hydrogeology and hydrologic conditions of the Ozark Plateaus aquifer system

The hydrogeology and hydrologic characteristics of the Ozark Plateaus aquifer system were characterized as part of ongoing U.S. Geological Survey efforts to assess groundwater availability across the Nation. The need for such a study in the Ozark Plateaus physiographic province (Ozark Plateaus) is highlighted by increasing demand on groundwater resources by the 5.3 million people of the Ozark Plateaus, water-level declines in some areas, and potential impacts of climate change on groundwater availability. The subject study integrates knowledge gained through local investigation within a regional perspective to develop a regional conceptual model of groundwater flow in the Ozark Plateaus aquifer system (Ozark system), a key phase of groundwater availability assessment. The Ozark system extends across much of southern Missouri and northwestern and north-central Arkansas and smaller areas of southeastern Kansas and northeastern Oklahoma. The region is one of the major karst landscapes in the United States, and karst aquifers are predominant in the Ozark system. Groundwater flow is ultimately controlled by aquifer and confining unit lithologies and stratigraphic relations, geologic structure, karst development, and the character of surficial lithologies and regolith mantle. The regolith mantle is a defining element of Ozark Plateaus karst, affecting recharge, karst development, and vulnerability to surface-derived contaminants. Karst development is more advanced—as evidenced by larger springs, hydraulic characteristics, and higher well yields—in the Salem Plateau and in the northern part of the Springfield Plateau (generally north of the Arkansas-Missouri border) as compared with the southern part of the Springfield Plateau in Arkansas, largely due to thinner, less extensive regolith and purer carbonate lithology. Precipitation is the ultimate source of all water to the Ozark system, and the hydrologic budget for the Ozark system includes inputs from recharge, losing-stream sections, and groundwater inflows and losses of water to gaining-stream sections, groundwater withdrawals, and surface-water and groundwater outflows to neighboring systems. Groundwater recharge, estimated by a soil-water-balance model, represents about 24 percent, or 11 inches, of 43.9 inches annual precipitation. Recharge is spatially variable, being greater in the northern Springfield Plateau and Salem Plateau than in the southern Springfield Plateau (generally south of the Arkansas border) because of differences in regolith mantle extent and thickness and carbonate lithology and hydraulic properties. Increased precipitation and decreased agricultural land use during the period 1951 through 2011 increased recharge by approximately 5 percent. Although all Ozark streams have losing, neutral, and gaining sections, they are dominantly gaining and are a net sink for groundwater with nearly 90 percent of groundwater recharge returned to springs and streams. Groundwater pumping is a small but important loss of water in the Ozark system hydrologic budget; water-level declines and local cones of depression have been observed around pumping centers and strong concerns exist over potential effects on stream and spring flow. Data indicate that societal needs for freshwater resources in the Ozark Plateaus will continue to increase and will do so in the context of changing climate and hydrology. Groundwater will continue to be an important part of supporting these societal needs and also local ecosystems. The unique character and hydrogeologic variability across the Ozark system will control how the system responds to future stress. Groundwater of the Ozark system in the northern study area is more dynamic, has greater storage and larger flux, and has greater potential for further development than in the part of the study area south of the Arkansas-Missouri border. Further south in Arkansas, a line exists, roughly defined as 5 miles south of the Springfield Plateau-Boston Mountains boundary, beyond which further extensive municipal or commercial development appears unlikely under current economic and resource-need conditions. A small part of the Ozark system groundwater budget is currently drafted for use, leaving an apparently large component available for further development and use—particularly in the northern Springfield Plateau and Salem Plateau; however, the effects of increased pumping on groundwater’s role in maintaining ecosystems and ecosystem services are not quantitatively well understood, and the close relation between groundwater and surface water highlights the importance of further quantitative assessment.

Arkansas, Kansas, Missouri, Oklahoma↗
USGS2011

Estimated hydrologic budgets of kettle-hole ponds in coastal aquifers of southeastern Massachusetts

Kettle-hole ponds in southeastern Massachusetts are in good hydraulic connection to an extensive coastal aquifer system that includes the Plymouth-Carver aquifer system on the mainland and aquifers underlying Cape Cod. The ponds receive water from, and contribute water to, the underlying glacial aquifer; ponds also receive water from precipitation and lose water to evaporation from the pond surface. Some ponds are connected to surface-water drainage systems and receive water from or contribute water to streams or adjacent wetlands. The Massachusetts Department of Environmental Protection currently (2011) is developing Total Maximum Daily Loads of phosphorus for the freshwater ponds in the region to maintain the health of pond ecosystems; the amounts and sources of water fluxes into and out of the ponds are important factors in determining the amount of phosphorus that can be assimilated into a pond. To assist in this effort, the U.S. Geological Survey used groundwater-flow models of the coastal aquifer system to estimate hydrologic budgets-including inflows and outflows from the aquifer system and adjacent streams and wetlands, and recharge from precipitation-for 425 ponds in southeastern Massachusetts. Water fluxes through the ponds are a function of several factors, including the size, shape, and bathymetry of the pond, orientation of the pond relative to the regional hydraulic gradient, and hydrologic setting relative to the proximity of groundwater divides and discharge boundaries. Total steady-state fluxes through the ponds range from more than 3,300,000 to less than 2,000 cubic feet per day. For ponds without surface-water inlets or outlets, groundwater inflow accounts for 98 to 3 percent of total inflow; conversely, recharge onto the pond surface accounts for the remainder of inflow (between 2 and 97 percent). All natural flows from these ponds are through recharge from the pond into the aquifer. In one pond, about 94 percent of the total outflow is removed for water supply. For ponds that are connected to surface-water drainages, most inflow and outflow are through streams. Ponds that receive water from streams receive most (58 to 89 percent) of their water from those streams. Ponds that are drained by streams lose between 5 and 100 percent of their water to those streams.

Scientific Investigations Report↗
USGS1978

A geological and geochemical reconnaissance of the Tathlith one-degree quadrangle, sheet 19/43, Kingdom of Saudi Arabia

The Tathlith one-degree quadrangle occupies an area of 11,620 sq km in the northeastern Asir region of the Kingdom of Saudi Arabia, in the southeastern part of the Precambrian shield. In the eastern part of the quadrangle the Precambrian rocks are covered by exposures of easterly-dipping sandstone of Cambrian or Ordovician age. A well-developed and highly integrated drainage system trending northward is worn into the Precambrian rocks, but for most of the year the wadis are dry. The Precambrian rocks of the quadrangle consist of an old, non-metamorphosed to variably metamorphosed sequence of volcanic and sedimentary rocks intruded by three main successions of plutonic and hypabyssal igneous rocks. The interlayered volcanic and sedimentary rocks occupy arcuate, north-trending fold belts in which old, rather tight north-trending folds have been refolded at least once by open folds with nearly east-trending axes. Old, north-trending left-lateral faults are associated with the fold belts and are themselves intersected by younger, northwest-trending faults. Motion on both sets of faults has been reactivated several times. The interlayered volcanic and sedimentary rocks are an eugeosynclinal sequence of graywacke and andesite with sparse marble, quartzite, and rhyolite. Andesite is the dominant component of the sequence. Plutonic or hypabyssal equivalents of the andesite intrude the volcanic-sedimentary sequence. In many places these rocks are essentially non-metamorphosed, but elsewhere they are faintly to strongly metamorphosed, or even polymetamorphosed. Dynamothermal metamorphism associated with the northerly folding, and contact metamorphism are the principal kinds of metamorphism. The metamorphic grade is mostly greenschist facies or albite-epidote amphibolite facies. The largest intrusive in the area is a batholith of regional dimension, the east side of which intrudes and divides the fold belts. Granite gneiss and granodiorite gneiss are the main components of the batholith. Biotite granite of calc-alkaline composition, and somewhat younger than the granite gneiss and granodiorite gneiss, forms northerly elongate to subcircular plutons in the gneisses and the rocks of the volcanic-sedimentary sequence.

Open-File Report↗
USGS2022

Selenium in the Kootenai River Basin, Montana and Idaho, United States, and British Columbia, Canada

Selenium entering the 90-mile long transboundary Koocanusa Reservoir (also called Lake Koocanusa) in southeastern British Columbia, Canada, and northwestern Montana, United States, has been measured at concentrations above State and Federal water-quality and aquatic life standards. The reservoir is within the international Kootenai (or “Kootenay” in Canada) drainage basin, which contains critical habitat for native fish species and is impounded by Libby Dam 16 miles upstream from Libby, Montana. Since 1984, selenium concentrations have ranged from below detection to greater than 8 micrograms per liter in the Elk River, measured 2.2 miles above its discharge into Koocanusa Reservoir at a British Columbia environmental monitoring station (site 0200016). Selenium is a required micro-nutrient, but elevated concentrations in water bioaccumulate in egg-laying fish and birds, causing various sublethal effects and death. One possible source of selenium in the Kootenai River Basin is the excavation of bedrock in the Elk River Valley to access coal seams for metallurgical steelmaking and coal production. Five open-pit coal mines are operating in this region of southeastern British Columbia that produce about 21 million tons of metallurgical coal annually. Site-specific selenium standards were established for the reservoir in 2020 following collaborative work by the U.S. Geological Survey, Montana Department of Environmental Quality, the British Columbia Ministry of Environment and Climate Change Strategy, the Lake Koocanusa Monitoring and Research Working Group, and the Selenium Technical Subcommittee. The standards of 0.8 microgram per liter for dissolved selenium in the water column and 15.1 milligrams per kilogram dry weight for fish egg (ovary) tissue (in addition to the muscle and wholebody standards) were adopted into Montana State law in 2020 and approved by the U.S. Environmental Protection Agency in 2021.

British Columbia, Idaho, Montana↗
USGS1975

Water resources of the Mississippi and Sauk Rivers Watershed, central Minnesota

A variety of glacial landforms (moraines, till plains, drumlin fields and outwash plains) characterized the 3,890-square mile Mississippi and Sauk Rivers watershed. Underlying the glacial drift are Cambrian and Precambrian sedimentary rocks in the southeastern part of the watershed and Precambrian igneous and metamorphic rocks elsewhere. Surface drainage is entirely to the Mississippi River, the largest tributary being the Sauk River, which drains an area of about 970 square miles. The Mississippi follows a regional topographic low and transects the watershed from north to south. Greatest relief is in the morainal area in the west-central part of the watershed. The outwash plain in the southeastern part of the watershed and associated terrace deposits along the Mississippi River form a large area of relatively low relief. Details of topography are shown on 7 ½ and 15’ U.S. Geological Survey quadrangle maps, as indexed. Agriculture is the major economic activity. Small communities are scattered throughout the watershed; most larger municipalities and related development are concentrated along the Mississippi River. Lakes and streams offer good recreational opportunities.

Minnesota↗
USGS2005

Lithology, hydraulic properties, and water quality of the Sandstone Aquifer in the northwestern part of the Bad River Indian Reservation, Wisconsin, 1998-1999

The Precambrian sandstone aquifer in the northwestern part of the Bad River Band of Lake Superior Tribe of Chippewa Indians Reservation, Ashland County, Wisconsin, provides much of the drinking water to area residents. A study was undertaken in cooperation with the Bad River Tribe to provide specific information about the lithology, hydraulic properties, and water quality of the sandstone aquifer. During 1998 and 1999, the U.S. Geological Survey installed three monitoring wells, collected and analyzed lithologic and water samples, and conducted geophysical logging and aquifer tests to characterize the sandstone aquifer. The two monitoring wells in the southeastern part of the study area, the Diaperville Monitoring Well #1 (Diaperville MW #1) and the Tolman Monitoring Well #1 (Tolman MW #1) , are believed to have encountered older Middle Proterozoic Oronto Group sandstones. The sandstone encountered in the Ackley Monitoring Well #1 (Ackley MW #1) is believed to be Chequamegon Sandstone of the Late Proterozoic Bayfield Group. This interpretation is based on previous studies, as well as thin- section analysis of sandstone core recovered from the Ackley Monitoring Well #1. Results of aquifer tests conducted in the Diaperville Monitoring Well #1 and the Tolman Monitoring Well #1 provide ranges for hydraulic param - eter values in the sandstone aquifer: transmissivity ranges from 83 to 509 square feet per day; hydraulic conductivity ranges from 1.6 to 4.5 feet per day; storativity ranges from 0.00019 to 0.00046; and specific capacity ranges from 0.22 to 0.67 gallons per minute per foot. Though high- and low-angle fractures are present in Ackley Monitoring Well #1 core, the hydraulic properties of the bedrock appear to be due largely to the matrix porosity measured in thin section (16–21 percent) and permeability of the sandstone. The aquifer test for the Diaperville Monitoring Well #1 resulted in observed drawdown in nearby glacial wells, evidence of a hydraulic connection between the sandstone aquifer and the glacial deposits. Major ion analyses indicate that the water sampled from the sandstone aquifer at the Ackley site is of the calcium-magnesium-sodium- bicarbonate type. Based on a single sampling set, volatile organic constituents were not detected in water samples from the Diaperville Monitoring Well #1 or the Ackley Monitoring Well #1.

Wisconsin↗
USGS2023

Sampling and analysis plan for the Koocanusa Reservoir and upper Kootenai River, Montana, water-quality monitoring program, 2021

In 2021, the U.S. Geological Survey will collect water-quality samples and environmental data from 3 sites in Koocanusa Reservoir and from 1 site in the Kootenai River. The transboundary Koocanusa Reservoir is in southeastern British Columbia, Canada, and northwestern Montana, United States, and was formed with the construction of Libby Dam on the Kootenai River 26 kilometers upstream from Libby, Montana. Two of the reservoir sites and the Kootenai River site, in the Libby Dam tailwater (the outflow of the reservoir flow into the Kootenai River), are equipped with automated, high-frequency ServoSipper water samplers. At the two reservoir sites, these samplers are mounted to pontoon platforms and automatically collect samples from multiple depths; a ServoSipper sampler was deployed at one site in 2019, and another ServoSipper sampler will be deployed at a second site in 2021. Discrete water-quality samples will be collected monthly at two depths at the river site and at two of the reservoir sites. The goal of this project is to collect multidepth, high-frequency vertical and temporal water-quality samples and data to understand the limnological and biological processes that control variations and trends in selenium concentrations and loads throughout Koocanusa Reservoir and in the Libby Dam tailwater at the southern end of the reservoir. This sampling and analysis plan documents the organization, sampling and data-collection scheme and design, pre- and post-collection processes, and quality-assurance and quality-control procedures.

Montana↗
USGS1987

Surface-water quality in Pequea Creek basin, Pennsylvania, 1977-79

A study of the Pequea Creek basin was conducted by the U.S. Geological Survey, in cooperation with the Susquehanna River Basin Commission and the EPA from February 1977 through March 1979. Pequea Creek drains an intensive agricultural area of 154 sq mi in southeastern Pennsylvania, and enters the Susquehanna River 30 mi north of the Chesapeake Bay. The study included measurement of streamflow and collection of water and bottom material samples from seven sites in the basin during selected base flows and storms. Water samples were collected daily at a site near the mouth of Pequea Creek, and analyzed for suspended sediment, nitrogen and phosphorus species, organic carbon, and pesticides. Some groundwater samples also were collected and analyzed for nitrate. Annual yields measured from the basin during the study period were 1,950 ton/sq mi for suspended sediment, 13.8 ton/sq mi for total nitrogen, and 1.8 ton/sq mi for phosphorus. These yields are five times higher than any previously measured in the Susquehanna River basin. The discharges of all constituents monitored increased with increasing flow, indicated that a large amount of material in the basin is available for transport to streams during storms. The large yields of nitrogen and phosphorus are probably caused by the intensive agriculture in the basin coupled with large applications of fertilizer and manure to farm fields. Chemical analyses of rainfall samples indicate that precipitation was not a significant source of nitrogen and phosphorus. Excluding nitrate, all constituents measured were transported mainly during storms. Nitrate concentrations during base flow were as high as 10 mg/L as N--the Environmental Protection Agency standard for domestic water supplies. Groundwater sampled from farm wells had nitrate concentrations up to 28 mg/L as N. The largest concentrations of herbicides detected in Pequea basin were for 2,4-D, atrazine, and simazine. The maximum concentrations observed during storms were 1.2, 24, and 5.4 micrograms/L, respectively. The insecticides chlordane and DDT had mean concentrations of 0.02 and 0.01 micrograms/L, respectively. Lindane, PCB, and heptachlor slightly exceed maximum limits during storms.

Pennsylvania↗
USGS1996

Environmental setting of benchmark streams in agricultural areas of eastern Wisconsin

This report describes the environmental setting of 20 benchmark streams in agricultural areas of eastern Wisconsin that are part of the Western Lake Michigan Drainages, National Water-Quality Assessment Program. Benchmark streams are defined as those that show minimal adverse effects from human activity, and they were selected on the basis of field reconnaissance and the following criteria: (1) available invertebrate or fisheries data that indicated good to excellent water quality, (2) instream habitat restoration for fisheries enhancement, and (3) land management to protect riparian vegetation. Information gathered from these benchmark sites can be used as a standard of reference to compare the health of other streams in agricultural areas on the basis of aquatic-biota communities, habitat, and water-quality characteristics. The information included in this report serves as background information that will be useful for a series of studies at these benchmark-stream sites in the Western Lake Michigan Drainages study unit as part of the National Water-Quality Assessment Program. Four relatively homogeneous units (RHU's) in agricultural areas that differed in bedrock and surficial geology were selected for study. RHU 1 (clayey surficial deposits over carbonate bedrock) and RHU 3 (sandy-till surficial deposits over carbonate bedrock) are in adjacent agricultural areas in the Southeastern Wisconsin Till Plains ecoregion. RHU 20 (sandy/sand and gravel surficial deposits over igneous and metamorphic bedrock) and RHU 26 (sandy/sand and gravel surficial deposits over sandstone bedrock) are in adjacent areas of agriculture and mixed forests in the North Central Hardwood Forests ecoregion. Differences in land use/land cover, and riparian vegetation and instream habitat characteristics are presented. Summaries of field measurements of water temperature, pH, specific conductance and concentrations of dissolved oxygen, total organic plus ammonia nitrogen, dissolved ammonium, nitrate plus nitrte as nitrogen, total phosphorus, dissolved orthophosphate, and atrazine are listed. Concentrations of dissolved oxygen for the sampled streams ranged from 6 A to 14.3 and met the standards set by the Wisconsin Department of Natural Resources (WDNR) for supporting fish and aquatic life. Specific conductance ranged from 98 to 753 u,Scm with values highest in RHU's 1 and 3, where streams are underlain by carbonate bedrock. Median pH did not vary greatly among the four RHU's and ranged from 6.7 to 8.8 also meeting the WDNR standards. Concentrations of total organic plus ammonia nitrogen, dissolved ammonium, total phosphorus, and dissolved orthophosphate show little variation between streams and are generally low, compared to concentrations measured in agriculturally-affected streams in the same RHU's during the same sampling period. Concentrations of the most commonly used pesticide in the study unit, atrazine, were low in all streams, and most concentrations were below trn 0.1 u,g/L detection limit. Riparian vegetation for the benchmark streams were characterized by lowland species of the native plant communities described by John T. Curtis in the "Vegetation of Wisconsin." Based on the environmental setting and water-quality information collected to date, these streams appear to show minimal adverse effects from human activity.

Wisconsin↗
USGS2024

State of science, gap analysis, and prioritization for southeastern United States water-quality impacts from coastal storms—Fiscal year 2023 program report to the Water Resources Mission Area from the Water Availability Impacts of Extreme Events Program—Hurricanes

Tropical cyclones (coastal storm events that include tropical depressions, tropical storms, and hurricanes) cause landscape-scale disturbances that can lead to impaired water quality and thus reduce water availability for use. Stakeholders and scientists at local and national scales have illustrated a need for understanding these risks to water quality. A regional and comprehensive understanding of the impacts of tropical storms and hurricanes on surface-water and groundwater quality—and thus water availability—is lacking for potentially impacted coastal and inland areas. As the U.S. Geological Survey considers development of tools to predict the extent to which water-quality impacts of hurricanes affect water availability, an assessment of the state of the science of hurricane impacts is needed, including a gap analysis and prioritization of data and science needs. This assessment focuses on the southeastern coastal States.

southeastern United States↗
USGS2017

Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown

The risk posed by intensification of North Atlantic hurricane activity remains controversial, in part due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Here we present a record of storm-triggered turbidite deposition offshore the Dry Tortugas, south Florida, USA, that spans abrupt transitions in North Atlantic sea-surface temperature and Atlantic Meridional Overturning Circulation (AMOC) during the Younger Dryas (12.9–11.7 ka). Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at that time, our record and numerical experiments suggest that strong hurricanes may have regularly affected Florida. Less severe surface cooling at mid-latitudes (∼20°–40°N) than across much of the tropical North Atlantic (∼10°–20°N) in response to AMOC reduction may best explain strong hurricane activity during the Younger Dryas near the Dry Tortugas and possibly along the entire southeastern coast of the United States.

Florida↗
USGS1938

Some mineral deposits of Glacier Bay and vicinity, Alaska

Prospecting in the Glacier Bay National Monument has been confined so far to granitic rocks near contacts with Paleozoic sediments, which they intrude.Near Reid Glacier thin veins, a few of which are traceable for about 300 feet both horizontaliy and vertically, trend northerly and carry sphalerite, galena, and pyrite. Gold was panned from some of the better looking material.Near Sandy Cove, 30 miles away, more irregular, but locally thicker, veins appear to carry only pyrite. Here pyrite also occurs along the contact between the granitic rocks and the intruded limestone.Sparse ore minerals have been seen at other places in and near the monument. As yet, no large mineral deposits have been found there, but many miles of igneous contacts have not been prospected. In southeastern Alaska, as elsewhere, such contacts are considered favorable places in which to search for mineral deposits.

Alaska↗
USGS1981

Surficial geologic map of the eastern Snake River Plain and adjacent areas, 111° -115° W., Idaho and Wyoming

This map portrays the distribution of surficial materials that cover most of the landscape of the eastern Snake River Plain and adjoining areas in a larger part of southeastern Idaho and a very small area in western Wyoming (fig. 1). Almost 350,000 people or 40 percent of Idaho's (estimating 1979 population from Rand McNally (1979)) live in the area, which constitutes about 30 percent of Idaho's land area. The great majority of this population resides in the major irrigated agricultural areas along the Snake River between American Falls and Ashton and between Bliss and Lake Walcott, which contain the important and growing commercial centers of Rexberg, Idaho Falls, Blackfoot, Pocatello, Burley-Rupert, Twin Falls, and Jerome. These areas encompass almost two-thirds of Idaho's irrigated croplands, and, along with water, are the region's most important resource. Major products include potatoes, sugar beets, alfalfa, small grains, and other crops. Along the margins of the Plain and in adjacent basins, smaller areas of irrigated farming and population are present, such as Teton Basin, Mud Lake area, Big and Little Lost River Valleys, Big and Little Wood River Valleys, and Raft River Valley. In several of these basins and in nearby upland areas, dry farming of grains is important. Some of these lands are now being converted to irrigated croplands. Grazing is the dominant economic use of grasslands on the Plain in adjacent basins and uplands. At present, industry assumes a minor role in the region's economy, although food processing and nuclear research at the Idaho National Engineering Laboratory (INEL) locally or important.

Idaho, Wyoming↗
USGS1982

Geology of the Jabal Riah area, Kingdom of Saudi Arabia

The Jabal Riah area is in the southern part of the Jibal al Hamdah quadrangle (lat 19?00'00'' to 19?07'S0'' N., long 45?37'30'' to 43?45'00' E.) in the southeastern Precambrian Shield, Asir Province, Kingdom of Saudi Arabia. The Jabal Mahanid group of ancient gold mines, which is part of the Jabal Ishmas-Wadi Tathlith gold belt, is in the west-central part of the area. Rocks in the Jabal Riah area consist of Precambrian layered metasedimentary and metavolcanic rocks intruded by Precambrian igneous rocks. The metamorphic rocks are, from oldest to youngest, interlayered hornblende and biotite schist, quartz-biotite schist, hornblende schist, serpentinite, and chlorite schist. The igneous rocks are, from oldest to youngest, diorite-gabbro including dikes, granodiorite, monzogranite-granodiorite, leucocratic quartz porphyry, rhyolite, and aplite and pegmatite dikes. A large area of jasper replaces serpentinite. On the valley floors, recent alluvium and pediment deposits overlie the bedrock. The structure of the area is dominated by a dome centered over the eastern border of the area; leucocratic quartz porphyry forms the core of the dome. Minor folds and faults are present. The Jabal Mahanid group of ancient gold mines is on a northwest-trending vein system, and major ancient mine areas are found where the system splits or changes direction. The veins consist of zones of brecciated and crushed rock, which are generally less than 0.5 m wide but may be as wide as 1 m. These zones contain quartz and calcite stringers and commonly are along hornblende schist-serpentinite contacts; however, they also cut both units. Most aplite, pegmatite, and quartz dikes in the area are thin and discontinuous and are intruded along the vein trend. Similar veins, at the same stratigraphic interval, have been found beyond the northeastern part of the map area. The veins contain detectable gold and silver (median gold, approximately 0.14 ppm; median silver, approximately 1 ppm). Gold and silver are most abundant in calcium-rich rocks and veins; silver was not detected in igneous rocks. Altered wall-rock zones are mineralized as much as 10 m away from the veins. Away from the Jabal Mahanid vein-system, silver was detected in the jasper. Gold and silver were detected in minor brecciated and sheared structures and in metasedimentary rocks. Gold was detected in sericitized margins of the leucocratic quartz porphyry, in unaltered rhyolite, and in aplite dikes. The presence of unusual amounts of gold and silver over a wide area is indicated by the ancient gold mines along veins at or near the hornblende schist-serpentinite contact in the map area and to the south in the Hajrah-Hamdah area and by the widespread evidence of precious metals in igneous rocks and other vein structures. A domed-shaped area, approximately 30 km in diameter, is outlined by the hornblende schist-serpentinite contact and has leucocratic quartz prophyry in the middle. Additional study of this area might reveal economic concentrations of gold and silver.

Open-File Report↗
USGS2001

Potentiometric surface, carbonate-rock province, southern Nevada and southeastern California, 1998-2000

The carbonate-rock aquifer that underlies most of southern Nevada occupies part of what is known as the carbonate-rock province, a physiographic region that encompasses the eastern two-thirds of the Great Basin. The potential for development of water resources in this aquifer has prompted Federal, State, and local authorities to seek additional information about the quality and quantity of ground water in the carbonate-rock province. Investigations of the region's hydrogeology have been ongoing since the early 1900's. U.S. Geological Survey studies dating from 1975 to 1996 used these data to identify temporal changes of water levels in wells, regional potentiometric surfaces, and the direction of regional ground-water flow in southern Nevada. In the current study, the ground-water potentiometric surface in a 20,000-square-mile section of the regional carbonate-rock aquifer in southern Nevada and southeastern California was identified based on interpretation of water-level data collected from 1998 through 2000. Also included are hydrographs that were constructed from water-level data collected from 1985 through 2000. The hydrographs and accompanying map provide a generalized picture of water levels in consolidated rocks of the southern portion of the carbonate-rock province. Interpretation of the potentiometric surface was constrained by the limited number of wells completed in the carbonate-rock aquifer.

Open-File Report↗
USGS2003

Tectonic Summaries for Web-served Earthquake Responses, Southeastern North America

This report documents the rationale and strategy used to write short summaries of the seismicity and tectonic settings of domains in southeastern North America. The summaries are used in automated responses to notable earthquakes that occur anywhere east of the Rocky Mountains in the United States or Canada. Specifically, the report describes the geologic and tectonic information, data sources, criteria, and reasoning used to determine the content and format of the summaries, for the benefit of geologists or seismologists who may someday need to revise the summaries or write others. These tectonic summaries are designed to be automatically posted on the World Wide Web as soon as an earthquake?s epicenter is determined. The summaries are part of a larger collection of summaries that is planned to cover the world.

Open-File Report↗
USGS1998

Hydrogeology and sources of recharge to the Buffalo and Wahpeton aquifers in the southern part of the Red River of the North drainage basin, west-central Minnesota and southeastern North Dakota

Declining hydraulic heads in the Buffalo and Wahpeton aquifers are of concern to the Minnesota Department of Natural Resources and local water managers because of limited groundwater resources in the southern part of the Red River of the North drainage basin. The U.S. Geological Survey, in cooperation with the Minnesota Department of Natural Resources and Moorhead Public Service, investigated the hydrogeology of and sources of recharge to the Buffalo and Wahpeton aquifers. The Buffalo aquifer is a complex, heterogeneous outwash deposit composed of medium to coarse sand and gravel. Part of the Buffalo aquifer is unconfined and part is confined. The direction of ground water flow in the Buffalo aquifer is from east to west. Water-level declines in observation wells near the Moorhead Public Service North Well Field extend beyond the eastern and western boundaries of the Buffalo aquifer. Transmissivity and storativity calculated from the drawdown part of an aquifer test ranged from 20,870 to 23,852 feet squared per day and from 3.0 x 10 -5 to 3.2 x 10 -2 , respectively. Transmissivity and hydraulic conductivity values of 29,090 and 28,450 feet squared per day and 272 and 266 feet per day were calculated from the recovery-phase data. Potential recharge from the Buffalo River and its tributaries to the Buffalo aquifer ranged from 5 to 14 cubic feet per second. Recharge from precipitation where the Buffalo aquifer is unconfined was about 1.49 x 10 5 cubic feet per day. Recharge per unit length of the Buffalo aquifer during an aquifer test near the Moorhead Public Service North Well Field ranged from 3.9 x 10 -4 to 2.0 x 10 -2 cubic feet per day. The Wahpeton Shallow Sand, the Wahpeton Sand Plain, and the Wahpeton Buried Valley aquifers comprise the Wahpeton aquifers in order of increasing depth. All the aquifers are composed of fine- to coarse-grained sand mixed with gravel. Confining units are interleaved with the Wahpeton aquifers. Ground-water-flow directions in the Wahpeton aquifers were changed by ground-water development. Before development, ground water flowed from the Wahpeton Buried Valley aquifer upward to the Wahpeton Sand Plain aquifer and the Wahpeton Shallow Sand aquifer. After development, ground water flowed from the Wahpeton Shallow Sand aquifer to the Wahpeton Sand Plain and the Wahpeton Buried Valley aquifers. The potential sources of recharge to the Wahpeton aquifers investigated were the Red River of the North, and adjacent hydro geologic units. The volume of ground water pumped from the Wahpeton aquifers provides an estimate of the upper limit for the volume of recharge to the aquifer. Based on pumpage from all of the Wapheton aquifers from 1990 to 1993, the upper limit is about 580 million gallons per year (2.4 x 10 5 cubic feet per day).

Minnesota, North Dakota↗
USGS1956

Summary of reconnaissance for radioactive deposits in Alaska, 1945-1954, and an appraisal of Alaskan uranium possibilities

In the period 1945-1954 over 100 investigations for radioactive source materials were made in Alaska. The nature of these investigations ranged from field examinations of individual prospects or the laboratory analysis of significantly radioactive samples submitted by prospectors to reconnaissance studies of large districts. In this period no deposits of uranium or thorium that would warrant commercial exploitation were discovered. The investigations, however, disclosed that radioactive materials occur in widely scattered areas of Alaska and in widely diverse environments. Many igneous rocks throughout Alaska are weakly radioactive because of uranium- and thorium-bearing accessory minerals, such as allanite, apatite, monazite, sphene, xenotime, and zircon; more rarely the radioactivity of these rocks is due to thorianite or thorite and their uranoan varieties. The felsic rocks, for example, granites and syenites, are generally more radioactive than the mafic igneous rocks. Pegmatites, locally, have also proved to be radioactive, but they have little commercial significance. No primary uranium oxide minerals have been found yet in Alaskan vein deposits, except, perhaps, for a mineral tentatively identified as pitchblende in the Hyder district of southeastern Alaska. However, certain occurrences of secondary uranium minerals, chiefly those of the uranite group, on the Seward Peninsula, in the Russian Mountains, and in the vicinity of Kodiak suggest that pitchblende-type ores may occur at depth beneath zones of alteration. Thorite-bearing veins have been discovered on Prince of Wales Island in southeastern Alaska. Although no deposits or carnotite-type minerals have been found in Alaska, several samples containing such minerals have been submitted by Alaskan prospectors. Efforts to locate the deposits from which these minerals were obtained have been unsuccessful, but review of available geologic data suggests that several Alaskan areas are potentially favorable for carnotite-type deposits. The chief of these areas is the Alaska Peninsula-Cook Inlet area which encompasses most of the reported occurrences of the prospectors' carnotite-type samples. Alaska is also potentially favorable for the occurrence of large bodies of the very low-grade uraniferous sedimentary rocks, such as phosphorites and black shales. This type of deposit, however, has not received much study because of the emphasis on the search for bonanza-type high-grade ores. Uraniferous phosphorites similar to those of Idaho, Montana, and Wyoming occur in northern Alaska on the north flank of the Brooks Range; black shales comparable to the uraniferous shales of the Chattanooga formation of southeastern United States have been noted along the Yukon River near the international boundary. Placer deposits in Alaska have some small potential for the production of the radioactive elements as byproducts of gold- and tin-placer mining. the placer area believed to have the relatively greatest potential in Alaska lies in the Kahiltna River valley where concentrates are known to contain such commercial minerals as ilmenite, cassiterite, platinum, and gold in addition to uranothorianite and monazite. The possibilities of the natural fluids--water and petroleum--have not yet been tested in Alaska to any great extent. Studies of fluids are in progress to determine whether they may be used to discover and define areas potentially favorable for the occurrence of uraniferous lodes.

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