Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Southeastern Geology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources
USGS1989

Geology of the Zambales ophiolite, Luzon, Philippines

The Zambales ophiolite of western Luzon, Philippines, exposes a typical succession of basalt flows, diabasic dikes, gabbro and tectonized harzburgite. The age established by limiting strata is late Eocene. Lack of evidence of thrust faulting and the general domal disposition of the lithologie units indicate that the ophiolitic rocks are exposed by uplift. Highly complex internal layered structures within the complex are related to processes developed during formation of the ophiolite and the Zambales ophiolite may be one of the least disturbed (by emplacement) ophiolitic masses known. The exposed mass trends north and the upper surface plunges at low angles (a few degrees) to the north and south. The chemistry and composition of the rocks in the northwest part of the Zambales area (Acoje block) is distinct from that in the southeastern segment (Coto block). The Acoje block, according to Evans (1983) and Hawkins and Evans (1983), resembles (on a chemical basis) arc-tholeiite series rocks from intra-island arcs and the rocks in the Coto block are typical back-arc basin rock series. The present writer believes that the ophiolite composes a single genetic unit and that the changes in composition are the result of changes that took place during the initial formation. The gabbro probably formed below a spreading center in an elongate, in cross section, V-shaped, magma chamber. The gabbro is estimated by the writer to be less than 2 km thick and may be less than 1 km in places. Numerous erosional windows through the gabbro in the northern and eastern side of the Zambales area show that the gabbro remaining in those areas is likely to be only a few hundred meters thick. Harzburgite is exposed to a depth of about 800 m in the Bagsit River area and this may be the deepest part of the ophiolite accessible for study on which there is any control on depth. A transitional zone, about 200 m thick lying between the gabbro and harzburgite, is composed of serpentinized dunite. Commonly the dunite contains disseminated sulfide minerals and at the Acoje Mines, platinum-group elements. A compositional layering within the gabbro is in places cumulate in the lower part of the unit but may have formed by nucleation higher up on the relatively steep sides of the magma chamber. A widespread gneissic banding in the gabbro forms large mappable structures which are many times more complex than is the disposition of the major rock units. These structures are believed to be the result of extensive slumping in the magma chamber. The structure produced by the cumulate layering merges with the gneissic banding, commonly without discernible change in attitude. This tectonic layered structure crosses the gabbro-peridotite boundary at any angle without seeming to disturb the original rock distribution. At greater depths below the boundary (ca. 800 m), the harzburgite contains low dipping banding, which probably reflects the result of differential movement within the mantle. Chromite occurs almost exclusively in a zone that generally lies no more than 200–300 m below the gabbro-peridotite boundary. Refractory-grade chromite is found in this zone below the olivine gabbro in the Goto block and as low-grade metallurgical grade chromite below norite in the Acoje block. At Acoje Mines the chromite is present in layers in dunite, which the writer interprets as being distributed in a zone along the gently dipping (ca. 25°) gabbro-peridotite boundary. The steeply dipping (ca. 60–80 ° ) individual layers lie en echelon along the boundary at an angle (ca. 50 ° ) to the contact. At Coto the chromite forms large discontinuous masses in the lowest dunite and in the uppermost harzburgite. Except for the chromite present as layers at Acoje, the regional tectonic layering crosses the chromite deposits without structural deviation. The chromite deposits and associated peridotite may be cumulate in origin, but have been modified to such an extent that cumulate textures are generally obliterated. The angle of repose of cumulate layers in the Acoje area and in the Coto block dip towards each other raising the possibility that the Zambales area may contain the relics of a spreading center. Initial emplacement of the Zambales ophiolite took place by uplift and the ultramafic portion was exposed to erosion in the earliest Miocene or late Oligocene. Submergence of some of the ophiolite followed the previous uplift and on the west side of the Zambales Range submergence of several kilometers is indicated. Final emergence appears to have taken place in Pliocene or Pleistocene time by block uplift and areas of greatest uplift closely conform to the present topographic surface.

Tectonophysics↗
USGS1964

Geology and ground-water resources of Rock County, Wisconsin

Rock County is in south-central Wisconsin adjacent to the Illinois State line. The county has an area of about 723 square miles and had a population of about 113,000 in 1957 ; it is one of the leading agricultural and industrial counties in the State. The total annual precipitation averages about 32 inches, and the mean annual temperature is about 48 ? F. Land-surface altitudes are generally between 800 and 00 feet, but range from 731 feet, where the Rock River flows into Illinois, to above 1,080 feet, at several places in the northwestern part of the county. The northern part of Rock County consists of the hills and kettles of a terminal moraine which slopes southward to a flat, undissected outwash plain. The southeastern part of the county is an area of gentle slopes, whereas the southwestern part consists of steep-sided valleys and ridges. Rock County is within the drainage basin of the Rock River, which flows southward through the center of the county. The western and southwestern parts of ,the county are drained by the Sugar River und Coon Creek, both of which flow into the Pecatonica River in Illinois and thence into the Rock River. The southeastern part of the county is drained by Turtle Creek, which also flows into Illinois before joining the Rock River. Nearly all the lakes and ponds are in the northern one-third of the county, the area of most recent glaciation. The aquifers in Rock County are of sedimentary origin and include deeply buried sandstones, shales, and dolomites of the Upper Cambrian series. This series overlies crystalline rocks of Precambrian age and supplies water to all the cities and villages in the county. The St. Peter sandstone of Ordovician age underlies all Rock County except where the formation has been removed by erosion in the Rock and Sugar River valleys, and perhaps in Coon Creek valley. The St. Peter sandstone is the principal source of water for domestic, stock, and small industrial wells in the western half of the county. This sandstone also yields some water to uncased wells that tap the deeper rocks of the Upper Cambrian series. East of the Rock River the Platteville, Decorah, and Galena formations undifferentiated, or Platteville-Galena unit, is the principal source of water for domestic and stock wells. Unconsolidated deposits of glacial origin cover most of Rock County and supply water to many small wells. In the outwash deposits along the Rock River, wells of extremely high capacity have been developed for industrial and municipal use. The most significant feature of the bedrock surface in Rock County is the ancestral Rock River valley, which has been filled with glacial outwash to a depth of at least 396 feet below the present land surface. East of the buried valley the bedrock has a fiat, relatively undissected surface. West of the valley the bedrock surface is rugged and greatly dissected. Ground water in Rock County occurs under both water-table and artesian conditions; however, because of the interconnection and close relation of all ground water in the county, the entire system is considered to be a single groundwater body whose surface may be represented by one piezometric map. Recharge occurs locally, throughout the county. Nearly all recharge is derived directly from precipitation that percolates downward to become a part of the groundwater body. Natural movement of water in the consolidated water-bearing units is generally toward the buried Rock and Sugar River valleys. Movement of water in the sandstones of Cambrian age was calculated to be about 44 million gallons a day toward the Rock River. Discharge from wells in Rock County in 1957 was about 23 million gallons a day. Nearly 90 percent of this water was drawn from the area along the Rock River. Drilled wells, most of which were drilled by the cable-tool method, range in diameter from 3 to 26 inches, and in depth from 46 to 1,225 feet. Driven wells in alluvium and glacial drift are usually 1? to 2? in

Wisconsin↗
USGS1967

Geology and ground-water resources of Laramie County, Wyoming

Laramie County, an area of 2,709 square miles, is in the southeast corner of Wyoming. Rocks exposed there range in age from Precambrian to Recent. The most extensive aquifers in the county are the White River Formation of Oligocene age, which is as much as 500 feet thick and consists predominantly of siltstone ; the Arikaree Formation of Miocene age, which consists of as much as 450 feet of very fine grained to fine-grained sandstone; and the Ogallala Formation of Miocene and Pliocene age, which consists ,of as much as 330 feet of gravel, sand, silt, and some cobbles and boulders. These formations are capable of yielding large ,supplies of water locally. Terrace deposits of Quaternary age yield moderate .to large supplies of water in the southeastern and northeastern parts of the county. In the Federal well field, large yields of water from the White River Formation are obtained from gravel lenses. In the eastern part of the county near Pine Bluffs, large yields are obtained from openings in .the siltstone of the White River. Previous investigators reported that the large yields were obtained in areas where the formation is fractured and fissured. The authors of this report believe that .the large yields from siltstone in the White River Formation are from pipes, sometimes called natural tunnels, rather than from fractures ,or fissures. Little is known about the water-bearing properties of the pro-Tertiary aquifers in the county, but water derived from the pro-Tertiary formations would probably be of poor quality, except in the vicinity of the outcrop near the western edge of the county. Precipitation is the principal source of recharge to the ground-water reservoirs. About 5 percent of the annual precipitation, or about 108,400 acre-feet per year, is estimated to be recharged. Only a small amount of additional recharge is from streams. The general movement of ground water is eastward, and the average gradient of the water table is about 40 feet per mile. The total amount ,of ground water pumped from wells in Laramie County during 1964 is estimated to be 28,000 acre-feet; about 6,000 acre-feet was used for municipal and industrial supplies, about 17,000 acre-feet was used for irrigation in the Pine Bluffs-Carpenter area, and about 5,000 acre-feet was used for other purposes. The balance of the recharge (80,400 acre-feet) is estimated to be discharged by the following means: 20 percent by underflow, 20 percent by streamflow, and 60 percent by evapotranspiration. The coefficient of transmissibility of the Ogallala Formation, determined by averaging data from 28 pumping tests made in the Cheyenne municipal well field, is about 16,000 gallons per day per foot. However, this figure is an average of the more permeable zones, and the average coefficient of transmissibility of the Ogallala in the county is probably much less because of the heterogeneous character of the formation. A coefficient of transmissibility of 3,800 gallons per day per foot was calculated for the Ogallala, in the same vicinity that the pumping tests were made, by using a regional method of analysis. Although the average transmissibility of the Ogallala is considered to be low, large yields are obtained from gravel stringers and lenses in the formation. The maximum perennial yield from the Cheyenne well field is estimated to be about 1.6 billion gallons per year. Moderate to large yields of water can be obtained in the north-central part of the county where the saturated thickness of the Arikaree Formation, or combined Arikaree and Ogallala Formations, is 200 feet or more. Ground water has been developed throughout the county, but development has been intensive only in the Cheyenne municipal well fields near Cheyenne and Federal and in the Pine Bluffs lowland. The water level has been lowered as much as 40 feet in the Cheyenne well field and somewhat less in the Federal well field.

Wyoming↗
USGS2007

Unique deep-water ecosystems off the southeastern United States

If nothing else, research in deep-sea environments teaches us how little we know about such important and productive habitats. The relatively recent discovery of hydrothermal-vent and cold-seep ecosystems illustrates this paucity of knowledge, and the subsequent explosion of research on these systems is a good example of the impact such concentrated efforts can have on marine sciences (see the March 2007 special issue of Oceanography on InterRidge, and Levin et al., 2007). The recent surge of interest in deep-sea corals is another example of how focused research on a particular subject can result in new perspectives on continental slope biotopes. Although deep-sea corals have been known for over 200 years, they were viewed as somewhat of a novelty, and research on them was sporadic, typically geologic, and usually only documented their occurrences (e.g., Stetson et al., 1962; Neumann et al., 1977; Paull et al., 2000).

Georgia;Florida;North Carolina;South Carolina↗
USGS2006

Early Cretaceous terrestrial ecosystems in East Asia based on food-web and energy-flow models

In recent years, there has been global interest in the environments and ecosystems around the world. It is helpful to reconstruct past environments and ecosystems to help understand them in the present and the future. The present environments and ecosystems are an evolving continuum with those of the past and the future. This paper demonstrates the contribution of geology and paleontology to such continua. Using fossils, we can make an estimation of past population density as an ecosystem index based on food-web and energy-flow models. Late Mesozoic nonmarine deposits are distributed widely on the eastern Asian continent and contain various kinds of fossils such as fishes, amphibians, reptiles, dinosaurs, mammals, bivalves, gastropods, insects, ostracodes, conchostracans, terrestrial plants, and others. These fossil organisms are useful for late Mesozoic terrestrial ecosystem reconstruction using food-web and energy-flow models. We chose Early Cretaceous fluvio-lacustrine basins in the Choyr area, southeastern Mongolia, and the Tetori area, Japan, for these analyses and as a potential model for reconstruction of other similar basins in East Asia. The food-web models are restored based on taxa that occurred in these basins. They form four or five trophic levels in an energy pyramid consisting of rich primary producers at its base and smaller biotas higher in the food web. This is the general energy pyramid of a typical ecosystem. Concerning the population densities of vertebrate taxa in 1 km2 in these basins, some differences are recognized between Early Cretaceous and the present. For example, Cretaceous estimates suggest 2.3 to 4.8 times as many herbivores and 26.0 to 105.5 times the carnivore population. These differences are useful for the evaluation of past population densities of vertebrate taxa. Such differences may also be caused by the different metabolism of different taxa. Preservation may also be a factor, and we recognize that various problems occur in past ecosystem reconstructions. Counts of small numbers of confirmed species and estimates of maximum numbers of species present in the basin are used for the analysis and estimation of energy flow. This approach applies the methods of modern ecosystem analysis. ?? 2005 Elsevier Ltd. All rights reserved.

Cretaceous Research↗
USGS1975

Stratigraphy of Atlantic coastal margin of United States north of Cape Hatteras: Brief survey

A synthesis of studies of sea-floor outcrops of the sedimentary wedge beneath the northeastern United States continental shelf and slope and a reassessment of coastal plain Mesozoic stratigraphy, particularly of the coastal margin, provide insight for estimating the oil and gas potential and provide geologic control for marine seismic investigations of the Atlantic continental margin. The oldest strata known to crop out on the continental slope are late Campanian in age. The Cretaceous-Tertiary contact along the slope ranges from a water depth of 0.6 to 1.5 km south of Georges Bank to 1.8 km in Hudson Canyon. Few samples are available from Tertiary and Late Cretaceous outcrops along the slope. Sediments of the Potomac Group, chiefly of Early Cretaceous age, constitute a major deltaic sequence in the emerged coastal plain. This thick sequence lies under coastal Virginia, Maryland, Delaware, southeastern New Jersey, and the adjacent continental shelf. Marine sands associated with this deltaic sequence may be present seaward under the outer continental shelf. South of the Norfolk arch, under coastal North Carolina, carbonate rocks interfinger with Lower Cretaceous clastic strata. From all available data, Mesozoic correlations in coastal wells between coastal Virginia and Long Island have been revised. The Upper-Lower Cretaceous boundary is placed at the transition between Albian and Cenomanian floras. Potential hydrocarbon source beds are present along the coast in the subsurface sediments of Cretaceous age. Potential reservoir sandstones are abundant in this sequence.

Atlantic coastal plain↗
USGS1969

Geology, hydrology, and water quality in the Fresno area, California

The Fresno area comprises about 1.400 square miles lying west of the foothills of the Sierra Nevada and east of the trough of the San Joaquin Valley. The rainfall averages less than 10 inches per year causing agricultural development to depend mainly on surface-water deliveries and ground-water pumpage. Surface-water deliveries and ground-water pumpage, however, vary considerably from year to year. For example, in agricultural year 1958 (April 1, 1958-March 31, 1959) surface-water deliveries were about 1,340,000 acre-feet and agricultural ground-water pumpage was about 1,740,000 acre-feet, but in agricultural year 1960 deliveries were only about 560,000 acre-feet and pumpage was about 2,520,000 acre-feet. Alluvial fans are the dominant geomorphic features in the area. Small alluvial fans have been formed near the foothills by the deposits from the numerous intermittent streams that lie both north and south of the Kings River. Thicker and much more extensive alluvial fans have been formed under most of the area by deposits from the San Joaquin and Kings Rivers. Geologic units in the area consist of consolidated rocks and unconsolidated deposits. In turn, consolidated rocks consist of basement complex of pre-Tertiary age and marine and continental sedimentary rocks of Cretaceous and Tertiary age. Unconsolidated deposits are of both Tertiary and Quaternary age. Most of the geologic units dip gently southwestward approximately paralleling the back slope of the Sierra Nevada. Although some of these geologic units are faulted, especially in the deep subsurface, faulting has not affected the occurrence and movement of fresh ground water. The basement complex crops out along the eastern border of the area and yields only small amounts of water to wells; the marine and continental sedimentary rocks do not crop out in the area and do not yield any water to wells. The unconsolidated deposits are divided into an older series of Tertiary and Quaternary age, and a younger series of Quaternary age. The continental deposits of Tertiary and Quaternary age crop out beneath the extreme southeastern part of the area and yield small amounts of water to wells, and the deposits of Quaternary age crop out over most of the area and yield more than 90 percent of the water pumped from wells. The deposits of Quaternary age in turn are divided into older alluvium, lacustrine and marsh deposits, younger alluvium, flood-basin deposits. and sand dunes. The older alluvium is by far the most important aquifer in the Fresno area. It consists of intercalated lenses of clay, silt, silty and sandy clay, clayey and silty sand, sand, gravel, cobbles, and boulders, and in general it is fine grained near the trough of the valley and beneath the alluvial fans of intermittent streams. In the older alluvium, yields to wells range from less than 20 gpm (gallons per minute) to more than 3,000 gpm. The lacustrine and marsh deposits occur only in the subsurface in the western part of the area. Consisting mostly of silt and clay, they are virtually impermeable and thus restrict the vertical movement of water. These deposits from oldest to youngest are designated the E-clay, the C-clay, and the A-clay. The E-clay is the thickest and most extensive of all the lacustrine and marsh deposits. Because the clays tend to confine ground water in the Fresno area, five water bodies are recognized. These are the unconfined water body, the shallow water body, the confined water body below the A-clay, the confined water body below the C-clay, and the confined water body below the E-clay. The unconfined water body underlies most of the Fresno area. The shallow and confined water bodies underlie parts of the extreme western part of the area. There, heads in successively underlying water bodies are less than those in overlying water bodies, indicating that some ground water moves slowly downward through the clays. From agricultural years 1957 to 1962, outflow in the area exceeded inflow. As a result, for this period, the Fresno area had a net deficit of about 2,890,000 acre-feet. This deficit was made up for mostly by a decline in ground water stored. Water levels in all water bodies have been declining over the years, yet when streamflow and canal deliveries are large they show a general rise. The general movement of ground water in the Fresno area is toward the southwest, although pumping depressions near Fresno and near the western part of the area, cause ground water to move northward, southward, and westward toward them.

California↗
USGS1982

Physiographic divisions and differential uplift in the Piedmont and Blue Ridge

The Piedmont and Blue Ridge are dynamic landscapes that have undergone substantial change since the orogenies that ended in late Paleozoic or, as some believe, early Mesozoic time. The southern Blue Ridge region south of Roanoke, Va., lies on the crest of a topographic uplift that corresponds to the eastern continental drainage divide. To the north, this uplift and divide cross the Appalachian Valley and form the crest of the Appalachian Plateaus as far north as central Pennsylvania. The northern Blue Ridge Mountains as well as parts of the Piedmont are on the eastern part of the uplift area. The southeastern margin of the uplift corresponds to a line within the Piedmont physiographic province that extends northeastward from the Tallapoosa River at the Fall Zone and crosses the Rappahannock River at the Fall Zone. The differential elevation on either side of this line is sharp in some places, as, for example, northeast of Atlanta, Ga. In other places, the difference in elevation is difficult to detect, and, in effect, the line becomes a broad monoclinal slope. The region as a whole can be divided into at least six broad subregions that have somewhat different histories in late geologic time. The Piedmont Lowlands subprovince, southeast of the uplifted area, is dominated by a monotonous topography of low rounded ridges and ravines largely underlain by saprolite on crystalline rocks. Isolated ranges of hills of greater relief are scattered across the region; those investigated are directly related to the presence of erosionally resistant rocks. Stream patterns as well as broad topographic forms indicate that although the southern part of the Piedmont Lowlands was probably once covered by younger sediments, this area has been exposed to erosion for a long time. In North Carolina, the inner part of the Piedmont Lowlands has strongly trellised stream patterns, which suggest that subaerial erosion was active for an even longer time period, perhaps since the latest orogeny. North of the Cape Fear River, the outer part of the Piedmont Lowlands was covered by either fluvial or marine sediments or both, probably during Miocene time. Tectonic activity has affected the Piedmont Lowlands in late geologic time. The Fall Zone that forms the southeast border is, at least in places, controlled by faults active in Tertiary time. Late faults have also been found in the Pine Mountain area of Georgia. Minor differences in relief affecting large regions within the Piedmont Lowlands may be related to different rates of uplift in addition to rock resistance, either past or present. The Piedmont northeast of the Potomac River (Northeastern Highlands) rises to more than 300 m in altitude. The major streams have convex profiles that steepen as they near the Coastal Plain. Unusually narrow valleys and broad upland surfaces indicate an increased rate of erosion and show that the relief is now or recently has been increasing because of uplift or tilting. West of the southern end of the Piedmont Lowlands is an area herein called the Southwestern Highlands that in some respects is similar. The area is crossed by two large streams that have convex profiles. The highest mountain ranges in the area rise to altitudes greater than 600 m. Northwest of the Piedmont Lowlands, the topography and relief are higher, and in some places, the rise is gradual, forming a Foothill zone between the Piedmont Lowlands and the high Blue Ridge. This zone is morphologically more complex than the Piedmont Lowlands. North of the Roanoke River, the foothills are commonly chains of isolated hills and ridges generally underlain by resistant rocks. The hills increase in height near the Blue Ridge, an indication that they owe their height to tectonism of late geologic age. South of the Yadkin River, the hills are believed to be residual, the remnants of a larger highland that has been only partially reduced to the lower relief of the general Piedmont surface. The

Professional Paper↗
USGS2006

Geologic map and coal stratigraphy of the Doty Mountain quadrangle, eastern Washakie basin, Carbon County, Wyoming

This report provides a geologic map of the Doty Mountain 7.5-minute quadrangle, located along the eastern flank of the Washakie Basin, Wyo. Geologic formations and individual coal beds were mapped at a scale of 1:24,000; surface stratigraphic sections were measured and described; and well logs were examined to determine coal correlations and thicknesses in the subsurface. Detailed measured sections are provided for the type sections of the Red Rim Member of the Upper Cretaceous Lance Formation and China Butte and Overland Members of the Paleocene Fort Union Formation. The data set was collected as part of a larger effort to acquire data on Upper Cretaceous and Tertiary coal-bearing rocks in the eastern Washakie Basin and southeastern Great Divide Basin. Regions in the eastern Washakie Basin and southeastern Great Divide Basin have potential for coal development and were considered previously for coal leasing by the U.S. Bureau of Land Management.

Scientific Investigations Map↗
USGS2007

Detrital mineral chronology of the Uinta Mountain Group: Implications for the Grenville flood in southwestern Laurentia

Numerous studies have shown that large quantities of Grenville-age detritus dominate Neoproterozoic to Cambrian arenites in southwest Laurentia (southwestern United States). U-Pb ages and Hf isotopic compositions of zircons and 40 Ar/ 39 Ar ages of white mica from clastic sedimentary rocks of the Neoproterozoic Uinta Mountain Group also indicate significant Mesoproterozoic detritus mixed with a variably abundant Archean component. Zircons with ages representative of the Paleoproterozoic basement in the eastern Uinta Mountains or the younger Paleoproterozoic rocks of the adjacent Yavapai-Mazatzal terranes were not observed. A limited range of initial ϵ Hf (∼90% between –3 and +3) for Mesoproterozoic zircons suggests derivation from a source region (or regions) characterized by mixing between juvenile and reworked older crust during Grenville orogenesis. The enriched Grenville-age basement proposed to underlie much of southeastern North America may be this source based on similarities of Hf isotopic data from Mesoproterozoic zircons in Mississippi River sand and available paleocurrent data. If so, then disruption of this supply in the Cambrian may be related to Iapetan rifting and, perhaps, the separation of the Precordillera terrane from Laurentia.

Geology↗
USGS1998

Carolina slate belt gold deposits in Virginia, North Carolina, South Carolina, and Georgia

The Southeastern United States, in particular, the Carolina slate belt of Virginia, North Carolina, South Carolina, and Georgia, has been an important region of mineral production (fig. 1). This region is thought to have major potential for containing large undiscovered deposits of gold and silver, as well as copper, lead, zinc, molybdenum, and tin. Gold production from the major mines (Haile, Brewer, Ridgeway, and Barite Hill) in South Carolina ranked sixth in the Nation in 1992. Despite the closing of all but one mine in 1997, the region continues to attract intense scrutiny by the mining industry. Current U.S. Geological Survey (USGS) efforts in the slate belt are led by a multidisciplinary team focused on an integrated, multistate, and multiyear project that has the potential to result in a fundamental reinterpretation of the economic geology of the region. The slate belt is considered a scientific frontier because of the rapid pace of data acquisition by the USGS, academia, and private sector geologists and because emerging concepts of its geologic evolution are controversial. Establishing the origin of the gold deposits is important, not only in guiding exploration, but for more accurate assessment of the potential for the occurrence of new deposits throughout the southern Appalachians. These efforts may result in further industry exploration that may lead to discovery of new economically viable mineral deposits, which would have a broad economic impact on the region. Another goal is to find ways to prevent human activities related to gold extraction from remobilizing toxic metals found in these deposits, which could have potential harmful effects on the environment.

Georgia, North Carolina, South Carolina, Virginia↗
USGS1995

Geohydrology, water quality, and nitrogen geochemistry in the saturated and unsaturated zones beneath various land uses, Riverside and San Bernardino counties, California, 1991-93

The U.S. Geological Survey, in cooperation with the Eastern Municipal Water District, the Metropolitan Water District of Southern California, and the Orange County Water District, has completed a detailed study of the Hemet groundwater basin. The quantity of ground water stored in the basin in August 1992 is estimated to be 327,000 acre-feet. Dissolved-solids concentration ranged from 380 to 700 mg/L (milligrams per liter), except in small areas where the concentration exceeded 1,000 mg/L. Nitrate concentrations exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 mg/L nitrate (as nitrogen) in the southeastern part of the basin, in the Domenigoni Valley area, and beneath a dairy in the Diamond Valley area. Seven sites representing selected land uses-- residential, turf grass irrigated with reclaimed water, citrus grove, irrigated farm, poultry farm, and dairy (two sites)--were selected for detailed study of nitrogen geochemistry in the unsaturated zone. For all land uses, nitrate was the dominant nitrogen species in the unsaturated zone. Although nitrate was seasonally present in the shallow unsaturated zone beneath the residential site, it was absent at moderate depths, suggesting negligible migration of nitrate from the surface at this time. Microbial denitrification probably is occurring in the shallow unsaturated zone. High nitrate concentrations in the deep unsaturated zone (greater than 100 ft) suggest either significantly higher nitrate loading at some time in the past, or lateral movement of nitrate at depth. Nitrate also is seasonally present in the shallow unsaturated zone beneath the reclaimed-water site, and (in contrast with the residential site), nitrate is perennially present in the deeper unsaturated zone. Microbial denitrification in the unsaturated zone and in the capillary fringe above the water table decreases the concentrations of nitrate in pore water to below the MCL before reaching the water table. Pore water in the unsaturated zone beneath the citrus grove site contains very high concentrations of nitrate. Even though there are zones of microbial denitrification, nitrate seems to be migrating downward to the water table. The presence of a shallow perched-water zone beneath the irrigated-farm site prevents the vertical movement of nitrate from the surface to the regional water table. Above the perched zone, nitrate concentrations in the unsaturated zone are variable, ranging from below the MCL to four times the MCL. Periodically, nitrate is flushed from the shallow unsaturated zone to the perched-water zone. The unsaturated zone pore-moisture quality could not be adequately addressed because of the very dry conditions in the unsaturated zone beneath the poultry-farm site. Surficial clay deposits prevent water from percolating downward. At the two dairy sites, nitrate loading in pore water at the surface was very high, as great as 7,000 mg/L. Microbial denitrification in the unsaturated zone causes such concentrations to decrease rapidly with depth. At a depth of 20 ft, nitrate concentration was less than 100 mg/L. In areas where the depth to water is less than 20 ft, nitrate loading to ground water can be very high, whereas in areas where depth to water is greater than 100 ft, most of the nitrate is microbially removed before reaching the water table.

California↗
USGS2014

Estimating flood magnitude and frequency for urban and small, rural streams in Georgia, South Carolina, and North Carolina, 2011

Reliable estimates of the magnitude and frequency of floods are essential for the design of transportation and water-conveyance structures, flood insurance studies, and flood-plain management. Flood-frequency estimates are particularly important in densely populated urban areas. The U.S. Geological Survey (USGS) used a multistate approach to update methods for determining the magnitude and frequency of floods in urban and small, rural streams that are not substantially affected by regulation or tidal fluctuations in Georgia, South Carolina, and North Carolina (Feaster and others, 2014). The multistate approach has the advantage over a single state approach of increasing the number of streamflow-gaging station (streamgages) available for analysis, expanding the geographical coverage that would allow for application of regional regression equations across state boundaries, and building on a previous flood-frequency investigation of rural streamgages in the Southeastern United States. This investigation was funded as part of a cooperative program of water-resources investigations between the USGS, the South Carolina Department of Transportation, and the North Carolina Department of Transportation. In addition, much of the data and information for the Georgia streamgages was funded through a similar cooperative program with the Georgia Department of Transportation.

Georgia, North Carolina, South Carolina↗
USGS1947

Preliminary report on the gypsum deposits near Iyoukeen Cove, Chicagof Island, southeastern Alaska

The only known gypsum deposits in Alaska are on northeastern Chichagof Island, southeastern Alaska, at Iyoukeen Cove (fig. 1). The area first developed and for a time worked by the Pacific Coast Gypsum Co. is approximately 1 mile upstream from the mouth of Gypsum Creek at an elevation of about 70 feet (fig. 2). The second deposit, known as the Gypsum-Camel property, is on tidewater 12 miles northeast of the mouth of Gypsum Creek (fig. 2). Iyoukeen Cove is about 35 air miles southwest of Juneau and is on both the mail-boat and the airline routes between Juneau and Sitka. The two deposits were examined by a Geological Survey party during the summer of 1946. Topographic and geologic maps were made of the vicinity of both deposits (figs. 2 and 3). Accessible underground workings at the Gypsum-Camel property also were mapped,

Alaska↗
USGS2002

Assessments of aquifer sensitivity on Navajo Nation and adjacent lands and ground-water vulnerability to pesticide contamination on the Navajo Indian Irrigation Project, Arizona, New Mexico, and Utah

The U.S. Environmental Protection Agency requested that the Navajo Nation conduct an assessment of aquifer sensitivity on Navajo Nation lands and an assessment of ground-water vulnerability to pesticide contamination on the Navajo Indian Irrigation Project. Navajo Nation lands include about 17,000 square miles in northeastern Arizona, northwestern New Mexico, and southeastern Utah. The Navajo Indian Irrigation Project in northwestern New Mexico is the largest area of agriculture on the Navajo Nation. The Navajo Indian Irrigation Project began operation in 1976; presently (2001) about 62,000 acres are available for irrigated agriculture. Numerous pesticides have been used on the Navajo Indian Irrigation Project during its operation. Aquifer sensitivity is defined by the U.S. Environmental Protection Agency as 'The relative ease with which a contaminant [pesticide] applied on or near a land surface can migrate to the aquifer of interest. Aquifer sensitivity is a function of the intrinsic characteristics of the geologic material in question, any underlying saturated materials, and the overlying unsaturated zone. Sensitivity is not dependent on agronomic practices or pesticide characteristics.' Ground-water vulnerability is defined by the U.S. Environmental Protection Agency as 'The relative ease with which a contaminant [pesticide] applied on or near a land surface can migrate to the aquifer of interest under a given set of agronomic management practices, pesticide characteristics, and aquifer sensitivity conditions.' The results of the aquifer sensitivity assessment on Navajo Nation and adjacent lands indicated relative sensitivity within the boundaries of the study area. About 22 percent of the study area was not an area of recharge to bedrock aquifers or an area of unconsolidated deposits and was thus assessed to have an insignificant potential for contamination. About 72 percent of the Navajo Nation study area was assessed to be in the categories of most potential or intermediate potential for contamination. About 6 percent of the study area was assessed to have the least potential for contamination, mostly in areas where the slope of the land surface is more than 12 percent. Nearly all fields on the Navajo Indian Irrigation Project were assessed to have the most potential for contamination. The assessment of ground-water vulnerability to pesticide contamination on the Navajo Indian Irrigation Project was based on pesticide application to various crops on part of the Navajo Indian Irrigation Project during 1997-99. The assessment indicated that ground water underlying fields of beans, wheat, barley, and alfalfa was most vulnerable to pesticide contamination; ground water underlying fields of corn and potatoes was intermediately vulnerable to pesticide contamination; and ground water underlying fields of hay was least vulnerable to pesticide contamination.

Arizona, New Mexico, Utah↗
USGS1978

Geologic map of the Casius Quadrangle of Mars

Geologic units of the martian surface are subdivided on the basis of surface morphology, albedo, and crater distribution and are placed in a stratigraphic sequence following principles of superposition, crosscutting relations, and, to a degree, crater density. The Casius quadrangle (30˚ N to 65˚ N lat; 240˚ W to 300˚ W long) is one of the northern tier of Lambert conformal sheets of the Mars Atlas. It consists of four distinctive physiographic regions: 1) part of the northern cratered plains which forms an incomplete annulus around the north polar region, 2) smooth lowland plains of Utopia Planitia across the central and southeastern part of the map, 3) mountainous terrain, in the Nilosyrtis Mensae region south of the lowland plains, consisting of distinct mountains with hummocky surfaces, and 4) cratered plateau in the southwest part of the map, forming the northern part of the large complex cratered region in the mid-latitudes of Mars. In the Casius quadrangle, the cratered plateau is broken by a set of linear to curved parallel-sided canyons on its northern margin.

IMAP↗
USGS1999

Ground-water levels and flow directions in the glacial sediments and the Lockport Dolomite in southeastern Darke and northeastern Preble counties, Ohio, July 1998

During the summer of 1997, the U.S. Environmental Protection Agency (USEPA) began an emergency removal action at the Lewisburg Drum Site in northern Preble County, Ohio. The site is about 3 miles west-northwest of the village of Lewisburg. The USEPA removed about 1,200 drums of waste ink from the site, as well as 2,500 cubic yards of contaminated soil and 100,000 gallons of ground water. Because of the potential for off-site migration of ground-water contamination, USEPA sampled residential wells in the area; results from the samples collected by USEPA indicated that the quality of water in some privately owned wells may have been affected by contaminants from the site. However, the directions of ground-water flow in the area were not known. In 1998, the U.S. Geological Survey (USGS), in cooperation with the USEPA, measure water levels in the vicinity of the site. This map will aid in the interpretation of the water-quality data collected by USEPA.

Ohio↗
USGS2003

Natural background concentrations of nutrients in streams and rivers of the conterminous United States

Determining natural background concentrations of nutrients in watersheds in the developed world has been hampered by a lack of pristine sampling sites covering a range of climatic conditions and basin sizes. Using data from 63 minimally impacted U.S. Geological Survey reference basins, we developed empirical models of the background yield of total nitrogen (TN) and total phosphorus (TP) from small watersheds as functions of annual runoff, basin size, atmospheric nitrogen deposition rate, and region-specific factors. We applied previously estimated in-stream loss rates to yields from the small watershed models to obtain estimates of background TN and TP yield and concentration throughout the stream/river network in 14 ecoregions of the conterminous United States. Background TN concentration varies from less than 0.02 mg L-1 in the xeric west to more than 0.5 mg L-1 along the southeastern coastal plain. Background TP concentration varies from less than 0.006 mg L-1 in the xeric west to more than 0.08 mg L-1 in the great plains. TN concentrations in U.S. streams and rivers currently exceed natural background levels by a much larger factor (6.4) than do TP concentrations (2.0). Because of local variation in runoff and other factors, the range of background nutrient concentrations is very large within some nutrient ecoregions. It is likely that background concentrations in some streams in these regions exceed proposed nutrient criteria.

Environmental Science & Technology↗