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

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At least 127 records · Page 7Linked to original sources
USGS1998

Geology, geochemistry, geophysics, mineral occurrences, and mineral resource assessment for the Commonwealth of Puerto Rico

The Commonwealth of Puerto Rico has been investigated over a very long period of time by earth scientists from many disciplines and with diverse objectives in the studies. This publication attempts to apply much of the geologic, geochemical, geophysical, and mineral occurrence information to a single objective focused on producing a mineral resource assessment for the Commonwealth of Puerto Rico. However, the value of this publication lies not within the results of the mineral resource assessment nor within the interactive PDF files which can be viewed on the screen, but within the geologic, geochemical, geophysical, and mineral occurrence digital map coverages and databases which can be used for their own unique applications. The mineral resource assessment of Puerto Rico represents compilation of several decades of mineral investigations and studies. These investigations have been the joint efforts of the U.S. Geological Survey, the Puerto Rico Department of Natural Resources, and the University of Puerto Rico. This report contains not only the mineral-resource assessment, but also much of the scientific evidence upon which the assessment was based.

Puerto Rico↗
USGS1978

United States Geological Survey Yearbook, fiscal year 1977

Fiscal 1977 marked the 98th year the U.S. Geological Survey has endeavored in the unceasing task of providing information about the Earth and its physical resources, and regulating the activities of lessees engaged in extracting petroleum and other minerals from the public domain. The past year also marked the beginning of a third and challenging mission, drawing upon the Survey's scientific talents, to explore and assess the petroleum potential of a vast 37,000 square miles expanse of Alaska's North Slope known as the National Petroleum Reserve in Alaska. The first two missions require detailed and continuing investigations of the location, character, and extent of the Nation's land, water, mineral, and energy resources; a continuing National Topographic Mapping Program; the classification of Federal lands for mineral and waterpower potential; and a continuing program of technical review, safety inspection and royalty auditing of the operations of private parties engaged in mineral development on Federal lands to assure standards of safety, environmental protection, resource conservation, and a fair market return to the public for the development of their resources.

Yearbook↗
USGS1989

Summary geochemical maps of the Harrison 1° x 2° quadrangle, Arkansas and Missouri

This map is the first in a folio of maps of the Harrison 1° x 2° quadrangle, Arkansas and Missouri, prepared under the Conterminous United States Mineral Assessment Program. Additional maps showing various other geologic aspects of the Harrison quadrangle will be published as U.S. Geological Survey Miscellaneous Field Studies Maps bearing the same serial number with different letter suffixes (MF-1994-B, -C, and so on). Geochemical studies of the Harrison lo x 2° quadrangle, Arkansas and Missouri, are part of a joint multidisciplinary study by the U.S. Geological Survey; the Division of Geology and Land Survey, Missouri Department of Natural Resources; and the Arkansas Geological Commission. The objective of the joint study is to assess the mineral-resource potential of the area by integrated geologic, geochemical, and geophysical investigations.

Arkansas, Missouri↗
USGS1976

Spectrographic and chemical analyses of geochemical samples from the McCarthy Quadrangle, Alaska

As an integral part of the Alaskan Mineral Resource Assessment Program, a geochemical reconnaissance survey was conducted in the McCarthy quadrangle during the summer of 1974. The investigation consisted of geochemical sampling, multielement chemical and spectrographic analyses, compilation of new and existing geochemical data, statistical evaluation of the total data set, and the generation of element distribution and abundance maps. The purpose of the survey was to define areas in the quadrangle that contain anomalous concentrations of metallic and nonmetallic elements. These studies are fundamental to a comprehensive evaluation of the mineral resource potential of the area and to assist in the discovery of additional economic mineral deposits. The first-large scale geochemical sampling and analytical surveys were initiated in the McCarthy quadrangle in the early 1960's with the inception of the Wrangell Mountain project by the U.S. Geological Survey. Since that time, levels of activity in geochemical sampling in the quadrangle have fluctuated. Each year, many geochemical samples have been collected concomitantly with geologic mapping, and was culminated under the Alaskan Minerals Resource Assessment Program 1974.

Alaska↗
USGS2012

Analyzing legacy U.S. Geological Survey geochemical databases using GIS: applications for a national mineral resource assessment

This report emphasizes geographic information system analysis and the display of data stored in the legacy U.S. Geological Survey National Geochemical Database for use in mineral resource investigations. Geochemical analyses of soils, stream sediments, and rocks that are archived in the National Geochemical Database provide an extensive data source for investigating geochemical anomalies. A study area in the Egan Range of east-central Nevada was used to develop a geographic information system analysis methodology for two different geochemical datasets involving detailed (Bureau of Land Management Wilderness) and reconnaissance-scale (National Uranium Resource Evaluation) investigations. ArcGIS was used to analyze and thematically map geochemical information at point locations. Watershed-boundary datasets served as a geographic reference to relate potentially anomalous sample sites with hydrologic unit codes at varying scales. The National Hydrography Dataset was analyzed with Hydrography Event Management and ArcGIS Utility Network Analyst tools to delineate potential sediment-sample provenance along a stream network. These tools can be used to track potential upstream-sediment-contributing areas to a sample site. This methodology identifies geochemically anomalous sample sites, watersheds, and streams that could help focus mineral resource investigations in the field.

Egan Range↗
USGS1909

Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming

This paper, which supplements the report on the geology and water resources of the southern half of the Black Hills, published in 1901, is the result of studies made at intervals during the years 1899 to 1907. It relates to an area of about 7,500 square miles, situated about half in South Dakota and half in the northeast corner of Wyoming (Pl. II), and covering the northern half of the Black Hills uplift and a wide area of adjacent plains. The report describes the geology of the sedimentary rocks - their stratigraphy, structure, and history - and discusses their mineral resources, including underground water, coal, gypsum, etc. It also contains information respecting surface waters available for irrigation and stock raising, timber, climate, and the history of the topographic development of the region. The crystalline rocks of the central portion of the Black Hills area and the various igneous rocks of later age are shown on some of the accompanying maps but without differentiation, as the study of their geology was not within the scope of the investigation; neither are their mineral resources considered here, for these are treated in other publications. In the field work I have been assisted mainly by Prof. C. C. O'Harra, of the School of Mines at Rapid, who has mapped the geology of large areas about Aladdin, the Devils Tower, Belle Fourche, and Rapid. Dr. W. S. Tangier Smith has mapped portions of the Bear Lodge and Nigger Hill uplifts, and Mr. C. A. Fisher has assisted in portions of the work. The geology of the region from Sturgis to a point beyond Spearfish Canyon was mapped by Prof. T. A. Jaggar, jr., with the assistance of Mr. J. M. Boutwell, in 1898 and 1899. It is desirable to repeat here the statement made in my previous report that all who study the geology of the Black Hills must feel impressed by the remarkably clear general conceptions of the geologic relations of this region afforded by the survey made by Mr. Henry Newton over a quarter of a century ago. In one short season, with many unfavorable conditions for traveling, he determined most of the broader features and recorded many of the essential details. His posthumous report, edited by Mr. G. K. Gilbert, will always remain a standard work on Black Hills geology. Later studies have added greatly to our knowledge of the details of the stratigraphy and structure, the distribution of the rocks and minerals, and the age of the beds, and have afforded means for a more complete elucidation of the geologic history, especially the physiographic development of the Black Hills region.

South Dakota, Wyoming↗
USGS1979

Investigations needed to stimulate the development of Jordan's mineral resources

The level of living that any society can attain is a direct function of the use it makes of all kinds of raw materials (soil, water, metals, nonmetals, etc.), all kinds of energy (both animate and inanimate), and all kinds of human ingenuity; and is an inverse function of the size of the population that must share the collective product. The relation between raw materials, energy and ingenuity is such that use of a large amount of one may offset the need for large amounts of others. The most vital raw materials are water, soil, and construction materials, for these are needed in large quantities and are hard to import. Metals, chemicals, and inanimate energy are necessary for industrialization. The more of these minerals a nation possess, the better, but not nation can hope to be self-sufficient in all of the m and therefore must trade for some essential materials. Jordan’s natural resources have been little explored. The grantitc-metamorphic terrane in the southeastern part of the Kingdom could contain deposits of tungsten, rare earths, feldspar, mica, fluorite etc. and the sedimentary terrane over much of the rest of the county is favorable for the occurrence of oil. Even if none of these minerals is found, however, Jordan’s other mineral resource, if fully explored and developed in the light of modern technology, will support a far higher level of living than her people now enjoy. Very likely she can increase her rainfall by about 10 percent by cloud seeding, and she undeveloped supplies in both surface and ground water that are sufficient to nearly double her usable water supply. Even if she does not have oil or have it in large quantities, she can buy it cheaply from neighboring counties, and in addition has undeveloped sources of hydroelectric power, large reserves of bituminous limestone, large reserves of nuclear power as uranium in phosphate rock, and can use solar and wind power for special purposes. Her large supplies of construction, fertilizer, and other chemical raw materials will not only satisfy her own needs, but will yield both raw materials and some manufactured products for export. And she has valuable resource of touristic interest in the form of incomparable scenery, antiquities, and holy places, which, if properly advertised, could well become her largest single source of foreign currency. Revenues obtained from this source and from the export of agricultural products, nonmetallic minerals, and mineral products should support foreign oil purchase of oil, machinery, and other products not mined or produced internally. Full development of Jordan’s economic potential will take years to achieve and involves many complex activities. One of the most essential is one that can be pressed in the early years, namely the gathering of facts and basic data concerning the character, extent, and distribution of her resources, and the uses that can be made of them. Without each fundamental data or the understanding of their meaning or the ways to use and apply them, costly developmental projects and similar efforts to raise the level of living are likely to have limited success at best. Basic data and mineral resources are best gathered and published by permanent government agencies, for private organizations and individual cannot afford to take the risks involved in gathering data that may not have an immediate economic return; and even if private parties do collect such data they are not likely to make them general available. Of the activities needed in the field of mineral resources, some are already underway as the established function of government agencies. No bureau however, seems to have responsibility for making geologic maps and for gathering data on such things as steam flow, composition and properties of minerals and rocks, or for investigating the uses to which Jordan’s minerals might be put. To satisfy these needs, a Geological Survey and a Bureau of Mineral Industries should be formed and placed in operation as quickly as possible. The task of collecting and interpreting basic data or mineral resources must be done largely by Jordanians, for only in this way will Jordan acquire the technical competence needed to use the information. Few Jordanians have enough training or experience to work independently in these fields now, however, so help from outside technicians would be necessary over an initial training period of several years. But the number of outside technicians should never exceed the number of Jordanian technicians, and for this reason, neither organization could have a staff of more than a few people during the early years of operation.

Open-File Report↗
USGS1974

Summary of activities, U.S. Geological Survey Saudi Arabian project, 1950 to 1974

The U. S. Geological Survey (USGS) first began work in the Kingdom of Saudi Arabia in 1950 under the sponsorship of the Ministry of Finance and National Economy. The basic objective of the work was to investigate the mineral and water resource potential in western Saudi Arabia, but little was known of the region and it therefore was necessary to prepare geographic and geologic maps. Aerial photographs were taken and controlled mosaics produced, some paid for by the USGS but most paid for by the Saudi Arabian government, and reconnaissance geologic mapping was undertaken until the USGS team left Saudi Arabia in 1955. This mapping, in cooperation with mapping of the Arabian American Oil Company, was compiled as a series of scale 1:500,000 geographic and geologic maps in Arabic and English covering all of Saudi Arabia. A total of 42 of these maps were prepared. Three scale 1:2,000,000 geographic and geologic maps in Arabic and English, covering the Arabian Peninsula, also were prepared from this work. All of the maps were printed in the United States and published by the USGS, the last in 1963. Other work done by the USGS between 1950 and 1955 included locating and examining ancient mines, indentifying the Wadi Fatima oolitic iron deposit and other iron deposits in northwest Saudi Arabia, and advising on many water supply problems including those for Riyadh, Qizan, Qunfudhah, Rabigh, Yenbo, Umm Lejh, and Al Wajh. The mapping work and the geologic investigations laid the groundwork for the more detailed studies that followed.

Open-File Report↗
USGS2010

Geologic map of the Bartlett Springs Fault Zone in the vicinity of Lake Pillsbury and adjacent areas of Mendocino, Lake, and Glenn Counties, California

The Lake Pillsbury area lies in the eastern part of the northern California Coast Ranges, along the east side of the transform boundary between the Pacific and North American plates (fig. 1). The Bartlett Springs Fault Zone is a northwest-trending zone of faulting associated with this eastern part of the transform boundary. It is presently active, based on surface creep (Svarc and others, 2008), geomorphic expression, offset of Holocene units (Lienkaemper and Brown, 2009), and microseismicity (Bolt and Oakeshott, 1982; Dehlinger and Bolt, 1984; DePolo and Ohlin, 1984). Faults associated with the Bartlett Springs Fault Zone at Lake Pillsbury are steeply dipping and offset older low to steeply dipping faults separating folded and imbricated Mesozoic terranes of the Franciscan Complex and interleaved rocks of the Coast Range Ophiolite and Great Valley Sequence. Parts of this area were mapped in the late 1970s and 1980s by several investigators who were focused on structural relations in the Franciscan Complex (Lehman, 1978; Jordan, 1975; Layman, 1977; Etter, 1979). In the 1980s the U.S. Geological Survey (USGS) mapped a large part of the area as part of a mineral resource appraisal of two U.S. Forest Service Roadless areas. For evaluating mineral resource potential, the USGS mapping was published at a scale of 1:62,500 as a generalized geologic summary map without a topographic base (Ohlin and others, 1983; Ohlin and Spear, 1984). The previously unpublished mapping with topographic base is presented here at a scale of 1:30,000, compiled with other mapping in the vicinity of Lake Pillsbury. The mapping provides a geologic framework for ongoing investigations to evaluate potential earthquake hazards and structure of the Bartlett Springs Fault Zone. This geologic map includes part of Mendocino National Forest (the Elk Creek Roadless Area) in Mendocino, Glenn, and Lake Counties and is traversed by several U.S. Forest Service Routes, including M1 and M6 (fig. 2). The study area is characterized by northwest-trending ridges separated by steep-sided valleys. Elevations in this part of the Coast Ranges vary from 1,500 ft (457 m) to 6,600 ft (2,012 m), commonly with gradients of 1,000 ft per mile (90 m per km). The steep slopes are covered by brush, grass, oak, and conifer forests. Access to most of the area is by county roads and Forest Service Route M6 from Potter Valley to Lake Pillsbury and by county road and Forest Service Route M6 and M1 from Upper Lake and State Highway 20. From the north, State Highway 261 provides access from Covelo. Forest Service Route M1 trends roughly north from its intersection with Route M6 south of Hull Mountain and through the Elk Creek and Black Butte Roadless areas to State Highway 261. Side roads used for logging and jeep trails provide additional access in parts of the area.

Open-File Report↗
USGS2010

Preliminary Aeromagnetic Map of Joshua Tree National Park and Vicinity, Southern California

This aeromagnetic map of Joshua Tree National Park and vicinity is intended to promote further understanding of the geology and structure in the region by serving as a basis for geophysical interpretations and by supporting geological mapping, water-resource investigations, and various topical studies. Local spatial variations in the Earth's magnetic field (evident as anomalies on aeromagnetic maps) reflect the distribution of magnetic minerals, primarily magnetite, in the underlying rocks. In many cases the volume content of magnetic minerals can be related to rock type, and abrupt spatial changes in the amount of magnetic minerals commonly mark lithologic or structural boundaries. Bodies of mafic and ultramafic rocks tend to produce the most intense magnetic anomalies, but such generalizations must be applied with caution because rocks with more felsic compositions, or even some sedimentary units, also can cause measurable magnetic anomalies. The database includes two ASCII files containing new aeromagnetic data and two ASCII files with point locations of the local maximum horizontal gradient derived from the aeromagnetic data. This metadata file describes the horizontal gradient locations derived from new and existing aeromagnetic data. This aeromagnetic map identifies magnetic features as a basis for geophysical interpretations; the gradients help define the edges of magnetic sources. This database updates geophysical information originally presented in smaller-scale formats and includes detailed aeromagnetic data collected by EON Geosciences, Inc.

Open-File Report↗
USGS2018

Aeromagnetic map of Mountain Pass and vicinity, California and Nevada

Magnetic investigations of Mountain Pass and vicinity were begun as part of an effort to study regional crustal structures as an aid to understanding the geologic framework and mineral resources of the eastern Mojave Desert. The study area, which straddles the state boundary between southeastern California and southern Nevada, encompasses Mountain Pass, which is host to one of the world’s largest rare earth element carbonatite deposits. The deposit is found along a north-northwest-trending, fault-bounded block that extends along the eastern parts of the Clark Mountain Range, Mescal Range, and Ivanpah Mountains. This Paleoproterozoic block is composed of a 1.7-Ga metamorphic complex of gneiss and schist that underwent widespread metamorphism and associated plutonism during the Ivanpah orogeny. The Paleoproterozoic rocks were intruded by a Mesoproterozoic (1.4 Ga) ultrapotassic alkaline intrusive suite and carbonatite body. The intrusive rocks include, from oldest to youngest, shonkinite, mesosyenite, syenite, quartz syenite, potassic granite, carbonatite, carbonatite dikes, and late shonkinite dikes. Generally speaking, magnetic anomalies reflect lateral changes in subsurface magnetization that can be used to infer subsurface geologic structure, revealing variations in lithology and delineating geologic features such as faults, plutons, volcanic rocks, calderas, and sedimentary basins. A regional aeromagnetic map was derived from statewide aeromagnetic maps of California and Nevada that were compiled from numerous surveys flown at various flightline altitudes and spacings. This compilation, although composed of surveys acquired using different specifications, allows seamless interpretation of magnetic anomalies across survey boundaries. In addition, a high-resolution aeromagnetic survey was flown by helicopter over parts of the Clark Mountain Range, Mescal Range, and Ivanpah Mountains. The resulting mapped magnetic anomalies show in much greater detail the complex subsurface structures in the Mountain Pass area.

California, Nevada↗
USGS2019

Airborne radiometric maps of Mountain Pass, California

Geophysical investigations of Mountain Pass and vicinity were begun as part of an effort to study regional crustal structures as an aid to understanding the geologic framework and mineral resources of the eastern Mojave Desert. The study area encompasses Mountain Pass, host to one of the world’s largest rare earth element carbonatite deposits. The deposit is found along a north-northwest-trending, fault-bounded block that extends along the eastern parts of the Clark Mountain Range, Mescal Range, and Ivanpah Mountains. This Paleoproterozoic block is composed of a 1.7-Ga metamorphic complex of gneiss and schist that underwent widespread metamorphism and associated plutonism during the Ivanpah orogeny. The Paleoproterozoic rocks were intruded by a Mesoproterozoic (1.4 Ga) ultrapotassic alkaline intrusive suite and carbonatite body. The intrusive rocks include, from oldest to youngest, shonkinite, mesosyenite, syenite, quartz syenite, potassic granite, carbonatite, carbonatite dikes, and late shonkinite dikes. The diverse physical properties of rocks that underlie the study area are well suited to geophysical investigations. Contrasts in radiogenic signatures between Paleoproterozoic crystalline basement, rocks of the Mesoproterozoic carbonatite body and the associated alkaline intrusive suite, Paleozoic carbonate rocks, Mesozoic granitoids, Tertiary volcanic rocks, and unconsolidated alluvium, for example, produce a distinctive pattern of radiometric anomalies that can aid in understanding the geologic framework and mineral resource potential of the eastern Mojave Desert. A high-resolution radiometric survey of Mountain Pass was flown by helicopter over parts of the Clark Mountain Range, Mescal Range, and Ivanpah Mountains. Aeroradiometric surveys measure the intensity and energy spectrum of gamma-ray radiation from the three most common naturally occurring radioelements: potassium ( 40 K), thorium ( 232 Th), and uranium ( 238 U). For 232 Th and 238 U, the source of the gamma-rays comes from their thallium ( 208 Tl) and bismuth ( 214 Bi) decay products, respectively, and, thus, concentrations for Th and U are referred to as “equivalent concentration,” assuming radioactive equilibrium. The concentrations of these radioelements can be used together to estimate changes in geochemistry and lithology. Carbonatite deposits typically have distinctive geophysical signatures because they are relatively dense, magnetic, and radiogenic. Specifically, the carbonatite and alkaline intrusive suite at Mountain Pass is ultrapotassic and contains relatively significant amounts of K, Th, and U, which can be delineated using airborne radiometric surveys.

California↗
USGS1995

Geologic map of the Mount Adams volcanic field, Cascade Range of southern Washington

One of the dominating peaks of the Pacific Northwest, Mount Adams, stands astride the Cascade crest, towering 3 km above the surrounding valleys. The icecapped 3742-m (12,276') stratovolcano has for centuries been called Pah-to by the region's indigenous people, who hold the mountain sacred as a symbol of continuity and a source of prosperity and inspiration. Comparable reverence helped secure inclusion of most of the great cone in the national wilderness system in 1964. Far less prominent than the central stratovolcano is an extensive field of subdued volcanic centers composing its heavily forested lowland periphery. Before the present investigation, little was known about the eruptive history, the distribution of eruptive vents, or the frequency, composition, and explosivity of past volcanic activity, for either the focal stratocone or the surrounding volcanic field. Our mapping began in 1981 as a Congressionally mandated assessment of the mineral- and geothermal-resource potential of the Mount Adams Wilderness (Hildreth and others, 1983). The project expanded to include assessment of the volcanic hazards and, as the long-lived eruptive complexity of the area became appreciated, it evolved into a fundamental investigation of how volcanoes work.

IMAP↗
USGS2026

Spectral characteristics and mapping of lithium-rich playas in the Basin and Range Province, western United States

This report presents a comprehensive set of prospectivity maps for lithium in brines located within the playas of the Basin and Range Province of western United States. The prospectivity assessment is based on criteria established in the descriptive deposit model outlined in a previous U.S. Geological Survey report, with a focus on regional remote sensing methodologies. The playas within the study area have been systematically ranked according to several key factors, including size, the presence and abundance of source rocks, vegetation as an indicator of water availability, documented prospects, and data products derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor. Notably, the deposits in the playa of Clayton Valley make it stand out as the sole lithium brine-producing playa in the United States. The ASTER sensor provides optimal regional coverage, characterized by a 60-kilometer swath width and unique multispectral capabilities that are not available with other remote sensing instruments. This report and the accompanying maps are intended to serve as resources for further multidisciplinary assessments of lithium or other elements or commodities where prospectivity can be inferred from the presence of proxies such as alteration minerals.

Arizona, Baja California, California, Chihuahua, I↗
USGS1905

Geology of the central Copper River region, Alaska

It is an interesting evidence of the prompt responsiveness of our governmental organization to popular needs that the year 1898, which saw the first rush of argonauts to Alaska as a result of the discovery of the Klondike in 1986, saw also several well-equipped Federal parties at work in the Territory, mapping its great waterways and mountain ranges, investigating the feasible means of transportation within it, laying out routes for future lines of communication, and studying the mineral resources and the plant and animal life. It is true that before that year, in which the general attention of the world was fixed upon our heretofore lightly regarded northern province, fur traders, adventurous travelers, and hardy prospectors had made little-heralded journeys through the interior, and that one or another of the governmental departments had had representatives on special errands within its borders, but the amount of private and public energy expended there in 1898 probably exceeded that of any ten previous years.

Alaska↗
USGS1982

The Alaska Mineral Resource Assessment Program: Guide to information about the geology and mineral resources of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska

The Ketchikan and Prince Rupert 1-degree by 2-degree quadrangles, which encompass about 16,000 km2 at the south tip of southeastern Alaska, have been investigated by integrated field and laboratory studies in the disciplines of geology, geochemistry, geophysics, and Landsat data interpretation to determine their mineral-resource potential. Mineral deposits in the study area have been mined or prospected intermittently since about 1900, and production of small tonnages of ores containing gold, silver, copper, lead, zinc, and tungsten has been recorded. Extensive exploration and development currently (1981) is underway at a molybdenum prospect about 65 km east of Ketchikan. Our mineral-resource assessment indicates that the area contains potentially significant amounts of those metallic commodities, as well as of molybdenum, iron, antimony, and barite. The results of these studies have been published in a folio of maps accompanied by descriptive texts, diagrams, tables, and pertinent references. The present report serves as a guide to these investigations, provides relevant background information, and integrates the component maps and reports. It also describes revisions to the geology based on studies completed since the folio was published and includes a list of specific and general references on the geology and mineral deposits of the study area.

Alaska↗
USGS2026

The United States Magnetotelluric Array and the National Impedance Map

The United States Magnetotelluric Array (USMTArray) data set, collected in the years 2006–2024, consists of more than 1,700 long-period magnetotelluric stations covering the entirety of the contiguous United States on a quasi-regular 70 km grid. Funding across multiple federal agencies was critical to sustaining this effort to its completion. Important components of the project included active guidance and participation from the MT community, the open and timely availability of all data, and the application of consistent instrumentation and robust data processing. Together with parallel advancement in the development of publicly available three-dimensional (3D) inversion codes, the USMTArray has revitalized the US magnetotelluric community and increased the visibility of magnetotellurics within the Earth-science community. Taken as a whole, these data are visualized as the National Impedance Map, which, together with a 3D synthesis conductivity model of the nation, reveals the electrical architecture of the contiguous US. USMTArray data are used by researchers worldwide for fundamental and applied studies, including investigations of continental architecture and evolution, estimation of hazards to critical infrastructure due to geomagnetic storms, and assessment of the nation's undiscovered geothermal and mineral resources. We here review the history and development of the project, discuss the challenges and successes in its execution, present the National Impedance Map and synthesis conductivity model, and highlight the breadth of research stemming from this rich data set.

conterminous United States↗