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At least 811 records · Page 45Linked to original sources

USGS1999

Analysis of land use change in urban environments

Metropolitan areas in the United States are growing at unprecedented rates, creating extensive urban landscapes. Many of the farmlands, wetlands, forests, and deserts that formed the America of 1900 have been transformed during the past 100 years into human settlements. Almost everyone has seen these changes to their local environment but without a clear understanding of their impacts. It is not until we study these landscapes from a spatial perspective and the time scale of decades that we can begin to measure the changes that have occurred and predict the impact of changes to come. The U.S. Geological Survey's (USGS) Urban Dynamics Research (UDR) program studies the landscape transformations that result from the growth of metropolitan regions over time. Using sources such as historic maps, aerial photographs, and Landsat satellite data, USGS scientists first assemble retrospective urban land use databases that reflect several decades of change. These databases are then used to analyze the effects of urbanization on the landscape, and to model urban growth and land use change under alternative growth scenarios.

Fact Sheet↗

USGS2013

Wyoming Basin Rapid Ecoregional Assessment

The overall goal of the Wyoming Basin Rapid Ecoregional Assessment (REA) is to provide information that supports regional planning and analysis for the management of ecological resources. The REA provides an assessment of baseline ecological conditions, an evaluation of current risks from drivers of ecosystem change (including energy development, fire, and invasive species), and a predictive capacity for evaluating future risks (including climate change). Additionally, the REA may be used for identifying priority areas for conservation or restoration and for assessing cumulative effects of multiple land uses. The Wyoming Basin REA will address Management Questions developed by the Bureau of Land Management and other agency partners for 8 major biomes and 19 species or species assemblages. The maps developed for addressing Management Questions will be integrated into overall maps of landscape-level ecological values and risks. The maps can be used to address the goals of the REA at a number of levels: for individual species, species assemblages, aquatic and terrestrial systems, and for the entire ecoregion. This allows flexibility in how the products of the REA are compiled to inform planning and management actions across a broad range of spatial scales.

Colorado;Idaho;Montana;Utah;Wyoming↗

USGS2014

A multiphased approach to groundwater investigations for the Edwards-Trinity and related aquifers in the Pecos County region, Texas

The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and public supply uses in the Pecos County region of western Texas. Resource managers would like to understand the future availability of water in the Edwards-Trinity aquifer in the Pecos County region and the effects of the possible increase or temporal redistribution of groundwater withdrawals. To provide resource managers with that information, the U.S. Geological Survey (USGS), in cooperation with the Middle Pecos Groundwater Conservation District, Pecos County, City of Fort Stockton, Brewster County, and Pecos County Water Control and Improvement District No. 1, completed a three-phase study of the Edwards-Trinity and related aquifers in parts of Brewster, Jeff Davis, Pecos, and Reeves Counties. The first phase was to collect groundwater, surface-water, geochemical, geophysical, and geologic data in the study area and develop a geodatabase of historical and collected data. Data compiled in the first phase of the study were used to develop the conceptual model in the second phase of the study. The third phase of the study involved the development and calibration of a numerical groundwater-flow model of the Edwards-Trinity aquifer to simulate groundwater conditions based on various groundwater-withdrawal scenarios. Analysis of well, geophysical, geochemical, and hydrologic data contributed to the development of the conceptual model in phase 1. Lithologic information obtained from well reports and geophysical data was used to describe the hydrostratigraphy and structural features of the groundwater-flow system, and aquifer-test data were used to estimate aquifer hydraulic properties. Geochemical data were used to evaluate groundwater-flow paths, water-rock interaction, aquifer interaction, and the mixing of water from different sources in phase 2. Groundwater-level data also were used to evaluate aquifer interaction, as well as to develop a potentiometric-surface map, delineate regional groundwater divides, and describe regional groundwater-flow paths. During phase 3, the data collected and compiled along with the conceptual information in the study area were incorporated into a numerical groundwater-flow model to evaluate the sustainability of recent (2008) and projected water-use demands on groundwater resources in the study area.

Texas↗

USGS2017

Magnetic monitoring in Saguaro National Park

On a sandy, arid plain, near the Rincon Mountain Visitor Center of Saguaro National Park, tucked in among brittlebush, creosote, and other hardy desert plants, is an unusual type of observatory—a small unmanned station that is used for monitoring the Earth’s variable magnetic field. Named for the nearby city of Tucson, Arizona, the observatory is 1 of 14 that the Geomagnetism Program of the U.S. Geological Survey operates at various locations across the United States and Territories. Data from USGS magnetic observatories, including the Tucson observatory, as well as observatories operated by institutions in other countries, record a variety of signals related to a wide diversity of physical phenomena in the Earth’s interior and its surrounding outer-space environment. The data are used for geomagnetic mapping and surveying, for fundamental scientific research, and for assessment of magnetic storms, which can be hazardous for the activities and infrastructure of our modern, technologically based society. The U.S. Geological Survey observatory service is an integral part of a U.S. national project for monitoring and assessing space weather hazards.

Arizona↗

USGS2002

The National Map - Geographic Names

Governments depend on a common set of base geographic information as a tool for economic and community development, land and natural resource management, and health and safety services. Emergency management and homeland security applications rely on this information. Private industry, nongovernmental organizations, and individual citizens use the same geographic data. Geographic information underpins an increasingly large part of the Nation's economy.

Fact Sheet↗

USGS1990

Surface-water hydrology of Honey Lake Valley, Lassen County, California, and Washoe County, Nevada

Honey Lake Valley straddles the state line of California and Nevada, about 35 miles north of Reno; about three-fourths of the area is in California. In this report, Honey Lake Valley (also referred to as the "basin") includes the entire area within the hydrographic boundary (fig. 1). Susanville, Calif., in the northwest part of the basin, is the largest town. Population is increasing rapidly both in the Susanville area and in the Reno area of adjacent Washoe County, Nev. Both Lassen and Washoe Counties have identified water resources in Honey Lake Valley as a possible source to meet their needs for future development. An important component of an assessment of the availability of additional long-term supply is an appraisal of surface-water resources. The U.S. Geological Survey, in cooperation with the California Department of Water Resources and the Nevada Division of Water Resources, began a hydrologic assessment of the area in 1987. The study was primarily an appraisal of ground-water resources, but it also included an assessment of surface-water resources. The purpose of this map report is to present the results of the surface-water assessment, including (1) a broad overview of surface-water conditions in the basin, (2) an estimate of mean annual streamflow to the valley floor, and (3) an evaluation of the characteristics of Honey Lake. This report will be republished by the U.S. Geological Survey as a Hydrologic-Investigations Atlas. Results of this study related to ground-water resources of the basin are discussed in a separate report (Handman and others, 1990) and are summarized in a short "Water Fact Sheet" by Handman (1990).

California, Nevada↗

USGS1952

Geology and pegmatites of part of the Fourmile area, Custer County, South Dakota

The Fourmile area, Custer County, S. Dak., is in pre-Cambrian metamorphic rocks that surround the granitic core of the Black Hills. The area is on the upright limb of an overturned anticline that plunges about 30° S. 10° E. Three new formations of metamorphic rocks are described that have a total thickness of at least 7, 700 feet. The oldest of these formations, the Ruby Creek quartz-mica schist, is more than 6,500 feet thick. The overlying Raver formation, about 200 feet thick, is composed of thin beds of amphibolite and hornblende schist, lime-silicate rock, cordierite-biotite schist, microcline-biotite schist, and other types of rock. The youngest formation, the Ruddock quartz-mica-feldspar schist, is more than 1,000 feet thick. The presence of kyanite, staurolite, cordierite, and sillimanite in the rocks indicate that they have been subjected to high-grade metamorphism. About 420 pegmatites were mapped in the Ruby Creek quartz-mica--schist and the Ruddock quartz-mica-feldspar schist. A few thin pegmatites in the Raver formation were not mapped. Most of the pegmatites are concordant with the schistosity and relict (?) bedding of the enclosing metamorphic rocks. They are as much as 250 feet thick and range from 10 to 2,600 feet in length. Nine pegmatites are zoned and are classified as heterogeneous pegmatites. The remainder are homogeneous pegmatites that are poorly zoned. The major constituents of the pegmatites are plagioclase, quartz perthite, and muscovite. The accessory minerals are tourmaline, apatite, garnet, and biotite. Beryl was observed in 15 of the pegmatites. The heterogeneous pegmatites contain commercial deposits of potash feldspar, mica (sheet and scrap), and beryl.

South Dakota↗

USGS2000

Finding your way with map and compass

A topographic map tells you where things are and how to get to them, whether you're hiking, biking, hunting, fishing, or just interested in the world around you. These maps describe the shape of the land. They define and locate natural and manmade features like woodlands, waterways, important buildings, and bridges. They show the distance between any two places, and they also show the direction from one point to another. Distances and directions take a bit of figuring, but the topography and features of the land are easy to determine. The topography is shown by contours. These are imaginary lines that follow the ground surface at a constant elevation; they are usually printed in brown, in two thicknesses. The heavier lines are called index contours, and they are usually marked with numbers that give the height in feet or meters. The contour interval, a set difference in elevation between the brown lines, varies from map to map; its value is given in the margin of each map. Contour lines that are close together represent steep slopes. Natural and manmade features are represented by colored areas and by a set of standard symbols on all U.S . Geological Survey (USGS) topographic maps. Woodlands, for instance, are shown in a green tint; waterways, in blue. Buildings may be shown on the map as black squares or outlines. Recent changes in an area may be shown by a purple overprint. A road may be printed in red or black solid or dashed lines, depending on its size and surface. A list of symbols is available from the Earth Science Information Center (ESIC).

Fact Sheet↗

USGS2011

From ridge to reef—linking erosion and changing watersheds to impacts on the coral reef ecosystems of Hawai‘i and the Pacific Ocean

Coral reef ecosystems are threatened by unprecedented watershed changes in the United States and worldwide. These ecosystems sustain fishing and tourism industries essential to the economic survival of many communities. Sediment, nutrients, and pollutants from watersheds are increasingly transported to coastal waters, where these contaminants damage corals. Although pollution from watersheds is one of many factors threatening coral survival, it is one that local people can have a profound influence on. U.S. Geological Survey scientists are using mapping, monitoring, and computer modeling to better forecast the effects of watershed changes on reef health. Working with communities in Hawai‘i and on other U.S. islands in the Pacific, they are helping to provide the science needed to make informed decisions on watershed and coral reef management.

Hawai'i↗

USGS2014

Arkansas Groundwater-Quality Network

Arkansas is the fourth largest user of groundwater in the United States, where groundwater accounts for two-thirds of the total water use. Groundwater use in the State increased by 510 percent between 1965 and 2005 (Holland, 2007). The Arkansas Groundwater-Quality Network is a Web map interface ( http://ar.water.usgs.gov/wqx ) that provides rapid access to the U.S. Geological Survey’s (USGS) National Water Information System (NWIS) and the U.S. Environmental Protection Agency’s (USEPA) STOrage and RETrieval (STORET) databases of ambient water information. The interface enables users to perform simple graphical analysis and download selected water-quality data.

Arkansas↗

USGS2018

U.S. Geological Survey (USGS) water-use websites

Explore U.S. Geological Survey (USGS) water-use websites to learn how and where the Nation's water use has changed over time! Learn how to find and access USGS water-use data shown in maps, graphs, visualizations, and information products. Gain a better understanding of water-use terms and USGS educational resources. Learn how to find and use USGS visualizations to see how water use has changed in each State, and explore county water withdrawals during 2015 to see which areas withdrew the most or least water.

Fact Sheet↗

USGS2002

Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

The Ammonoosuc Volcanics, Partridge Formation, and the Oliverian and Highlandcroft Plutonic Suites of the Bronson Hill anticlinorium (BHA) in axial New England are widely accepted as a single Middle to Late Ordovician magmatic arc that was active during closure of Iapetus. Mapping and U–Pb dating indicate, however, that the BHA contains two volcano-sedimentary-intrusive sequences of probable opposite subduction polarity, here termed the Ammonoosuc and Quimby sequences. The Ammonoosuc sequence is defined by the Middle Ordovician Ammonoosuc Volcanics near Littleton, N.H., the type area, northeast to Milan, N.H., and Oquossoc, Me.; it also includes black slate of the Partidge Formation ( C. bicornis zone graptolites, ∼457 Ma). Related metamorphosed intrusive are the tonalitic Joslin Turn pluton (469±2 Ma), the Cambridge Black granitic pluton (468±3 Ma), and gabbro, tonalite (467±4 Ma), and sheeted diabase of the Chickwolnepy instructions. These intrusives cut lowermost Ammonoosuc (therefore >469 Ma). Probable uppermost Ammonoosuc is dated at 465±6 and 461±8 Ma. Successively below the Ammonoosuc are the Dead River and Hurricane Mountain Formations (flysch and melange), and the Jim Pond Formation (484±5 Ma) and Boil Mountain Complex (both ophiolite), which are structurally underlain by the Neoproterozoic(?) Chain Lakes massif. The Quimby sequence is defined by the Lower Silurian(?) to Upper Ordovician Quimby Formation, composed of bimodal volcanics (443±4 Ma) and sulfidic shale and graywacke that lie conformably to unconformably above the Ammonoosuc Volcanics and Partridge Formation. Also in the Quimby sequence are several granitic to sparsely gabbroic plutons of the Highlandcroft (441–452 Ma) and Oliverian (435–456 Ma) Plutonic Suites, which intrude the Dead River, Ammonoosuc and Partridge, but not the Quimby Formation. Based on faunal, paleolatitude, and isotropic data, the Ammonoosuc sequence and its correlative and underlying sequences formed off the southern Laurentian margin, but northwest of the principal Iapetan suture, or Red Indian line (RIL). The Boil Mountain–Jim Pond–Hurricane Mountain sequence was ramped northwestward over the Chain Lakes massif at ∼475 Ma, on the basal Boil Mountain surface. This obduction probably occurred slightly before obduction on the Baie Verte–Brompton surface (BBL), farther NW, over the Laurentian margin, and was followed by Dead River flysch sedimentation, which ended with the abrupt onset of Ammonoosuc-sequence arc magmatism at ∼470 Ma. Ammonoosuc eruptions probably ended at ∼460 Ma, when Iapetus closed along the Red Indian line. During a following magmatic hiatus of ∼3–5 m.y., now represented by portions of the Partridge Formation that overlie the Ammonoosuc Volcanics, subduction polarity reversed, and subduction resumed below the northwest-dipping Brunswick subduction complex (BSC) of New Brunswick, Canada. Quimby-sequence magmatism (∼456–435 Ma) on the the newly accreted Laurentian margin occurred above the BSC, whose footwall is now buried to the southeast by mainly Silurian clastic sediments of the Merrimack–Fredericton trough, deposited in the “Fredericton Sea”. In Silurian to Early Devonian time, the NW-dipping BSC footwall was paired with a SE-dipping subduction zone that produced arc magmas of the Coastal Volcanic belt, built on the composite Avalon and adjacent peri-Avalonian terranes. Orogen-normal extension produced by rapid rollback of both subduction zones narrowed the Fredericton Sea, produced the Central Maine and Connecticut Valley–Gaspé basins, and culminated in the Acadian orogeny when the sea completely closed in Early Devonian time.

Maine, New Hampshire↗

USGS2003

Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

The Ammonoosuc Volcanics, Partridge Formation, and the Oliverian and Highlandcroft Plutonic Suites of the Bronson Hill anticlinorium (BHA) in axial New England are widely accepted as a single Middle to Late Ordovician magmatic arc that was active during closure of Iapetus. Mapping and U–Pb dating indicate, however, that the BHA contains two volcano-sedimentary-intrusive sequences of probable opposite subduction polarity, here termed the Ammonoosuc and Quimby sequences. The Ammonoosuc sequence is defined by the Middle Ordovician Ammonoosuc Volcanics near Littleton, NH, the type area, northeast to Milan, NH, and Oquossoc, ME; it also includes black slate of the Partridge Formation ( C. bicornis ––zone graptolites, ∼457 Ma). Related metamorphosed intrusives are the tonalitic Joslin Turn pluton (469 ± 2 Ma), the Cambridge Black granitic pluton (468 ± 3 Ma), and gabbro, tonalite (467 ± 4 Ma), and sheeted diabase of the Chickwolnepy intrusions. These intrusives cut lowermost Ammonoosuc (therefore >469 Ma). Probable uppermost Ammonoosuc is dated at 465 ± 6 and 461 ± 8 Ma. Successively below the Ammonoosuc are the Dead River and Hurricane Mountain Formations (flysch and melange), and the Jim Pond Formation (484 ± 5 Ma) and Boil Mountain Complex (both ophiolite), which are structurally underlain by the Neoproterozoic(?) Chain Lakes massif. The Quimby sequence is defined by the Lower Silurian(?) to Upper Ordovician Quimby Formation, composed of bimodal volcanics (443 ± 4 Ma) and sulfidic shale and graywacke that lie conformably to unconformably above the Ammmonoosuc Volcanics and Partridge Formation. Also in the Quimby sequence are several granitic to sparsely gabbroic plutons of the Highlandcroft (441–452 Ma) and Oliverian (435–456 Ma) Plutonic Suites, which intrude the Dead River, Ammonoouc and Partridge, but not the Quimby Formation. Based on faunal, paleolatitude, and isotopic data, the Ammonoosuc sequence and its correlatives and underlying sequences formed off the southern Laurentian margin, but northwest of the principal Iapetan suture, or Red Indian line. The Boil Mountain-Jim Pond-Hurricane Mountain sequence was ramped northwestward over the Chain Lakes massif at ∼475 Ma, on the basal Boil Mountain surface. This obduction probably occurred slightly before obduction on the Baie Vert-Brompton surface (BBL), farther NW, over the Laurentian margin, and was followed by Dead River flysch sedimentation, which ended with the abrupt onset of Ammonoosuc-sequence arc magmatism at ∼470 Ma. Ammonoosuc eruptions probably ended at ∼460 Ma, when Iapetus closed along the Red Indian line. During a following magmatic hiatus of ∼3–5 m.y., now represented by portions of the Partridge Formation that overlie the Ammonoosuc Volcanics, subduction polarity reversed, and subduction resumed below the northwest-dipping Brunswick subduction complex (BSC) of New Brunswick, Canada. Quimby-sequence magmatism (∼456–435 Ma) on the newly accreted Laurentian margin occurred above the BSC, whose footwall is now buried to the southeast by mainly Silurian clastic sediments of the Merrimack-Fredericton trough, deposited in the “Fredericton Sea”. In Silurian to Early Devonian time, the NW-dipping BSC footwall was paired with a SE-dipping subduction zone that produced arc magmas of the Coastal Volcanic belt, built on the composite Avalon and adjacent peri-Avalonian terranes. Orogen-normal extension produced by rapid rollback of both subduction zones narrowed the Fredericton Sea, produced the Central Maine and Connecticut Valley-Gaspé basins, and culminated in the Acadian orogeny when the sea completely closed in Early Devonian time.

Maine, New Hampshire↗

USGS2004

Deposition, erosion, and bathymetric change in South San Francisco Bay: 1858-1983

Since the California Gold Rush of 1849, sediment deposition, erosion, and the bathymetry of South San Francisco Bay have been altered by both natural processes and human activities. Historical hydrographic surveys can be used to assess how this system has evolved over the past 150 years. The National Ocean Service (NOS) (formerly the United States Coast and Geodetic Survey (USCGS), collected five hydrographic surveys of South San Francisco Bay from 1858 to 1983. Analysis of these surveys enables us to reconstruct the surface of the bay floor for each time period and quantify spatial and temporal changes in deposition, erosion, and bathymetry. The creation of accurate bathymetric models involves many steps. Sounding data was obtained from the original USCGS and NOS hydrographic sheets and were supplemented with hand drawn depth contours. Shorelines and marsh areas were obtained from topographic sheets. The digitized soundings and shorelines were entered into a Geographic Information System (GIS), and georeferenced to a common horizontal datum. Using surface modeling software, bathymetric grids with a horizontal resolution of 50 m were developed for each of the five hydrographic surveys. Prior to conducting analyses of sediment deposition and erosion, we converted all of the grids to a common vertical datum and made adjustments to correct for land subsidence that occurred from 1934 to 1967. Deposition and erosion that occurred during consecutive periods was then computed by differencing the corrected grids. From these maps of deposition and erosion, we calculated volumes and rates of net sediment change in the bay. South San Francisco Bay has lost approximately 90 x 106 m3 of sediment from 1858 to 1983; however within this timeframe there have been periods of both deposition and erosion. During the most recent period, from 1956 to 1983, sediment loss approached 3 x 106 m3/yr. One of the most striking changes that occurred from 1858 to 1983 was the conversion of more than 80% of the tidal marsh to salt ponds, agricultural, and urban areas. In addition, there has been a decline of approximately 40% in intertidal mud flat area. Restoration of these features will require a detailed understanding of the morphology and sediment sources of this complex system.

California↗

USGS2018

Characterizing the subsurface geology in and around the U.S. Army Camp Stanley Storage Activity, south-central Texas

Several U.S. Geological Survey projects, supported by the National Cooperative Geologic Mapping Program, have used multi-disciplinary approaches over a 14-year period to reveal the surface and subsurface geologic frameworks of the Edwards and Trinity aquifers of central Texas and the Arbuckle-Simpson aquifer of south-central Oklahoma. Some of the project achievements include advancements in hydrostratigraphic mapping, three-dimensional subsurface framework modeling, and airborne geophysical surveys as well as new methodologies that link geologic and groundwater flow models. One area where some of these milestones were achieved was in and around the U.S. Army Camp Stanley Storage Activity, located in northwestern Bexar County, Texas, about 19 miles northwest of downtown San Antonio.

Texas↗

USGS2019

Santa Rosa's past and future earthquakes

Santa Rosa is no stranger to earthquakes. This northern California city was damaged several times in the late 19th and early 20th centuries by shaking from earthquakes, culminating in the devastating earthquake of 1906, whose rupture passed 20 miles to the west of the city on the San Andreas Fault. Then in 1969, Santa Rosa was again strongly shaken and buildings were damaged by a pair of nearby, moderate-sized earthquakes on the Rodgers Creek Fault. Since then, scientists have learned how the underlying geology increases shaking damage in Santa Rosa, have mapped where the Rodgers Creek Fault runs beneath the city, and have discovered that this fault is capable of much larger earthquakes. Following the 1969 earthquakes, Santa Rosa rose to the challenge of improving seismic safety; however, continued progress is needed to increase seismic resilience and reduce the impact of future earthquakes.

California↗

USGS1983

Geophysical and geologic studies in southern Mecklenburg County and vicinity, North Carolina and South Carolina

Geophysical methods consisting of gravity, aeromagnetics and aeroradioactivity have been applied to part of the Charlotte and Carolina slate belts in southern Mecklenburg County and vicinity to help interpret geology, lithology and structure. High aeroradioactivity is associated with potassium-rich granitic plutons, muscovite-rich gneisses, schists, and metavolcanic rocks; positive gravity and magnetic anomalies are associated with gabbro plutons; and negative gravity anomalies are associated with granitic plutons. At the west side of the slate belt, the Tillery phyllite is interpreted as having undergone progressive metamorphism. The underlying Uwharrie Formation extends into the Charlotte belt where it is mapped as metavolcanic rocks. Gravity models of the Carolina slate belt indicate that it is a synform containing a wedge of metasedimentary and volcanoclastic rock on plutonic basement. The basement is exposed in the adjacent Charlotte belt antiform. The northern Charlotte belt contains mainly plutonic rocks which have been divided into 3 supergroups of plutons based upon chemistry, mineralogy, texture, and age. They are: 1. Old Plutonic supergroup - plutons 545-490 m.y. that are medium to coarse-grained tonalite, quartz diorite, and granodiorites. 2. Concord-Salisbury supergroup -- plutons 426-350 m.y. which form sheet-like intrusions of differentiated gabbro; local volcanic centers with ring complexes 13 km in diameter that suggest magma chambers 0 - 8 km deep; smaller bodies of diorite, monzonite, and syenite; and small Salisbury type granodiorites. 3. Landis supergroup -- plutons 350-280 m.y. that are usually very coarse-grained, porphyritic, 'big feldspar,' potassium-rich granites. The Mecklenburg-Weddington gabbro complex of the Concord-Salisbury supergroup, the largest feature in the study area, contains three large gabbro plutons. The gabbro intruded old Plutonic complex rocks and could-have produced the metamorphic reaction K-feldspar + sillimanite quartz + muscovite reflected in the mineral assemblage of adjacent felsic metavolcanic rocks. Gravity models indicate a lopolith 3.5- to 4.5-km thick with a 2 km sill extending to the northeast. Positive magnetic and gravity anomalies suggest the lopolith is. connected with the Concord gabbro complex to the northeast. The sheet-like intrusions of Concord-Salisbury group gabbros, forming the core of the composite 5atholith, have medium-grained Salisbury type granodiorite above, and coarser-grained Landis granite below. The position of the supergroups as presently exposed may be a function of level of erosion versus level of emplacement. The plutons in the composite batholith span 200 m.y. according to current age data and are arranged with the oldest at the top and the youngest at the bottom. However, Rb-Sr and K-At ages in the Piedmont are more likely to reflect age of crustal uplift than the age of metamorphism or intrusion. The Charlotte belt composite batholith, therefore, may very well be the result of a shorter single tectonic event or process.

North Carolina, South Carolina↗

USGS2003

Geologic map of the Buckeystown quadrangle, Frederick and Montgomery Counties, Maryland, and Loudoun County, Virginia

The Buckeystown quadrangle is underlain mostly by rocks of the western Piedmont province and a portion of the eastern Blue Ridge province. The western Piedmont province is underlain by Late Proterozoic(?) and Lower Cambrian(?) metasedimentary rocks of the Westminster terrane, Lower and Middle Cambrian metasedimentary rocks and Upper Cambrian to Lower Ordovician carbonate rocks of the Frederick Valley synclinorium, Upper Triassic sedimentary rocks of the Mesozoic Culpeper basin, and Early Jurassic dikes; Lower Cambrian metasedimentary rocks underlie the Blue Ridge province. Within the western Piedmont, Lower Cambrian(?) metasedimentary rocks of the Sugarloaf Mountain anticlinorium are interpreted to be exposed in a tectonic window (A.A. Drake, Jr., U.S. Geological Survey, oral commun., 1989; Horton and others, 1989; Rankin and others, 1989) through the complexly deformed allochthonous rocks of the Westminster terrane (Muller and others, 1989). The undated rocks of the Westminster terrane are interpreted to be rise-slope deep-water deposits of the Iapetus Ocean that were transported westward onto the Laurentian margin (ancestral North America) along the Martic thrust fault during the Ordovician Taconic orogeny (Horton and others, 1989). Continental margin strata, which underlie the Sugarloaf Mountain anticlinorium and continental margin-slope strata which underlie the Frederick Valley synclinorium, are here correlated with the Lower Cambrian Chilhowee Group and overlying carbonate rocks on the limbs of the Blue Ridge-South Mountain anticlinorium to the west. The relation of the Sugarloaf Mountain Quartzite (Jonas and Stose, 1938b) to surrounding rocks is controversial (Scotford, 1951; Stose and Stose, 1951; Thomas, 1952). The Martic thrust fault (Jonas, 1924, 1927; Knopf and Jonas, 1929) and the interpretation that the Sugarloaf Mountain anticlinorium (Scotford, 1951; Thomas, 1952) is a tectonic window through the Martic thrust sheet (A.A. Drake, Jr., U.S. Geological Survey, oral commun., 1989) further complicate the stratigraphic correlation of these rocks. Upper Triassic sedimentary rocks of the Culpeper basin consist of westward-dipping conglomerate, sandstone, and siltstone. These rocks, as well as intrusive Early Jurassic diabase dikes, accumulated during an early Mesozoic rifting event that resulted in the opening of the Atlantic Ocean. Contractional faults of Paleozoic orogenesis and extensional faults related to Mesozoic rifting indicate a complex tectonic history for this region. Cenozoic deposits, which overlie the bedrock, include high- and low-level alluvial terraces, residual gravel, colluvium, and alluvium. Terrace deposits of the ancestral Potomac River and the Monocacy River are as much as 183 ft and 140 ft, respectively, above the present river levels. Isolated residual gravel deposits that form in place from the weathering of the Upper Cambrian Frederick Formation superficially resemble terrace deposits. Colluvium of quartzite boulders is concentrated in hillslope depressions on Sugarloaf Mountain, and fanlike aprons of colluvial quartz pebbles cover the Triassic rocks on the west side of the Culpeper basin. Alluvium was mapped along the Potomac and Monocacy Rivers and all their tributaries. Altitude ranges from 200 ft along the Potomac River to 1,282 ft on the crest of Sugarloaf Mountain. The map area includes the Chesapeake and Ohio Canal National Historical Park, and the Monocacy Natural Resources Area. Sugarloaf Mountain is a registered natural landmark. Parts of the Buckeystown quadrangle were mapped by Jonas and Stose (1938a, scale 1:62,500), Scotford (1951, scale 1:12,500), Thomas (1952, scale 1:25,000), Cloos and Cook (1953, 1:62,500), Reinhardt (1974, scale 1:62,500), Froelich 1975, scale 1:62,500), and Lee (1979, scale 1:24,000). The map area is subdivided into five domains. Allochthonous rocks of the Westminster terrane are thrust onto rocks of the Frederick Valley synclinorium. Within the Westminster terrane of Muller and others (1989), the Sugarloaf Mountain Quartzite and Urbana Formation underlie the parautochthonous Sugarloaf Mountain anticlinorium. The Lower and Middle Cambrian Araby Formation and Upper Cambrian Frederick Formation crop out on the east limb of the Frederick Valley synclinorium. The Frederick Formation and Upper Cambrian and Lower Ordovician Grove Formation lie in the trough of the Frederick Valley synclinorium. Lower Cambrian Harpers, Antietam, and Tomstown Formations crop out on the east limb of the Blue Ridge-South Mountain anticlinorium in the extreme northwest corner of the map. The Blue Ridge-South Mountain anticlinorium is separated from the Frederick Valley synclinorium by Upper Triassic sedimentary rocks in the Culpeper basin half graben.

Maryland, Virginia↗