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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 37 records · Page 2Linked to original sources
USGS2011

Chloride control and monitoring program in the Wichita River Basin, Texas, 1996–2009

Water resources of the Wichita River Basin in north-central Texas are vital to the water users in Wichita Falls, Tex., and surrounding areas. The Wichita River Basin includes three major forks of the Wichita River upstream from Lake Kemp, approximately 50 miles southwest of Wichita Falls, Tex. The main stem of the Wichita River is formed by the confluence of the North Wichita River and Middle Fork Wichita River upstream from Truscott Brine Lake. The confluence of the South Wichita River with the Wichita River is northwest of Seymour, Tex. (fig. 1). Waters from the Wichita River Basin, which is part of the Red River Basin, are characterized by high concentrations of chloride and other salinity-related constituents from salt springs and seeps (hereinafter salt springs) in the upper reaches of the basin. These salt springs have their origins in the Permian Period when the Texas Panhandle and western Oklahoma areas were covered by a broad shallow sea. Over geologic time, evaporation of the shallow seas resulted in the formation of salt deposits, which today are part of the geologic formations underlying the area. Groundwater in these formations is characterized by high chloride concentrations from these salt deposits, and some of this groundwater is discharged by the salt springs into the Wichita River.

Texas↗
USGS2008

An evaluation of selected extraordinary floods in the United States reported by the U.S. Geological Survey and implications for future advancement of flood science

Thirty flood peak discharges determine the envelope curve of maximum floods documented in the United States by the U.S. Geological Survey. These floods occurred from 1927 to 1978 and are extraordinary not just in their magnitude, but in their hydraulic and geomorphic characteristics. The reliability of the computed discharge of these extraordinary floods was reviewed and evaluated using current (2007) best practices. Of the 30 flood peak discharges investigated, only 7 were measured at daily streamflow-gaging stations that existed when the flood occurred, and 23 were measured at miscellaneous (ungaged) sites. Methods used to measure these 30 extraordinary flood peak discharges consisted of 21 slope-area measurements, 2 direct current-meter measurements, 1 culvert measurement, 1 rating-curve extension, and 1 interpolation and rating-curve extension. The remaining four peak discharges were measured using combinations of culvert, slope-area, flow-over-road, and contracted-opening measurements. The method of peak discharge determination for one flood is unknown. Changes to peak discharge or rating are recommended for 20 of the 30 flood peak discharges that were evaluated. Nine floods retained published peak discharges, but their ratings were downgraded. For two floods, both peak discharge and rating were corrected and revised. Peak discharges for five floods that are subject to significant uncertainty due to complex field and hydraulic conditions, were re-rated as estimates. This study resulted in 5 of the 30 peak discharges having revised values greater than about 10 percent different from the original published values. Peak discharges were smaller for three floods (North Fork Hubbard Creek, Texas; El Rancho Arroyo, New Mexico; South Fork Wailua River, Hawaii), and two peak discharges were revised upward (Lahontan Reservoir tributary, Nevada; Bronco Creek, Arizona). Two peak discharges were indeterminate because they were concluded to have been debris flows with peak discharges that were estimated by an inappropriate method (slope-area) (Big Creek near Waynesville, North Carolina; Day Creek near Etiwanda, California). Original field notes and records could not be found for three of the floods, however, some data (copies of original materials, records of reviews) were available for two of these floods. A rating was assigned to each of seven peak discharges that had no rating. Errors identified in the reviews include misidentified flow processes, incorrect drainage areas for very small basins, incorrect latitude and longitude, improper field methods, arithmetic mistakes in hand calculations, omission of measured high flows when developing rating curves, and typographical errors. Common problems include use of two-section slope-area measurements, poor site selection, uncertainties in Manning’s n -values, inadequate review, lost data files, and insufficient and inadequately described high-water marks. These floods also highlight the extreme difficulty in making indirect discharge measurements following extraordinary floods. Significantly, none of the indirect measurements are rated better than fair, which indicates the need to improve methodology to estimate peak discharge. Highly unsteady flow and resulting transient hydraulic phenomena, two-dimensional flow patterns, debris flows at streamflow-gaging stations, and the possibility of disconnected flow surfaces are examples of unresolved problems not well handled by current indirect discharge methodology. On the basis of a comprehensive review of 50,000 annual peak discharges and miscellaneous floods in California, problems with individual flood peak discharges would be expected to require a revision of discharge or rating curves at a rate no greater than about 0.10 percent of all floods. Many extraordinary floods create complex flow patterns and processes that cannot be adequately documented with quasi-steady, uniform one-dimensional analyses. These floods are most accurately described by multidimensional flow analysis. Within the U.S. Geological Survey, new approaches are needed to collect more accurate data for floods, particularly extraordinary floods. In recent years, significant progress has been made in instrumentation for making direct discharge measurements. During this same period, very little has been accomplished in advancing methods to improve indirect discharge measurements. Greater use of paleoflood hydrology could fill many shortcomings of U.S. Geological Survey flood science today, such as enhanced knowledge of flood frequency. Additional links among flood runoff, storm structure, and storm motion would provide more insight to flood hazards. Significant improvement in understanding flood processes and characteristics could be gained from linking radar rainfall estimation and hydrologic modeling. Additionally, more could be done to provide real-time flood-hazard warnings with linked rainfall/runoff and flow models. Several important recommendations are made to improve the flood-documentation capability of the U.S. Geological Survey. When very large discharges are measured by current meter or hydroacoustics, water-surface slope should be measured as well. This measurement would allow validation of roughness values that can significantly extend the discharge range of verified Manning’s n for 1-dimensional and 2-dimensional flow analyses. At least two of the floods investigated may have had flow so unstable that large waves affected the interpretation of high-water marks. Instability criteria should be considered for hydraulic analysis of large flows in high-gradient, smooth channels. The U.S. Geological Survey needs to modernize its toolbox of field and office practices for making future indirect discharge measurements. These practices could include, first and foremost, a new peak-flow file database that allows greater description and interpretation of flow events, such as stability criteria in high-gradient, smooth channels, debris flow documentation, and details of flood genesis (hurricane, snowmelt, rain-on-snow, dam failure, and the like). Other modernized practices could include (a) establishment of calibrated stream reaches in chronic flash flood basins to expedite indirect computation of flow; (b) development of process-based theoretical rating curves for streamflow-gaging stations; (c) adoption of step-backwater models as the standard surface-water modeling tool for U.S. Geological Survey field offices; (d) development and support for multidimensional flow models capable of describing flood characteristics in complex terrain and high-gradient channels; (e) greater use of the critical-depth method in appropriate locations; (f) deployment of non-contact instruments to directly measure large floods, rather than attempting to reconstruct them; (g) increased use of paleoflood hydrology; and (h) assurance that future collection of hydro-climatic data meets the needs of more robust watershed models.

Scientific Investigations Report↗
USGS1999

Michael Tuomey's 1848 geological survey of South Carolina

One hundred and fifty years ago, Michael Tuomey completed his 'Report on the Geology of South Carolina,' the result of four years of arduous labor. The report is the first detailed and comprehensive geological description of the entire state, and it includes a geological map that shows the distribution of Coastal Plain and Piedmont-Blue Ridge units. In the sesquicentennial of Tuomey's survey, it is fitting that we recognize his important early contribution to the geology of South Carolina and the southeast. Tuomey's report is a 293-page volume with a 48-page appendix and an index. Although he gave a complete depiction of Coastal Plain geology and delineated Cretaceous, Lower Eocene, Eocene, Miocene, Post-Pliocene, and alluvial units on his map, the emphasis herein is on his mapping of the Piedmont and Blue Ridge. The metamorphic units he delineated are clay slate, mica slate, talcose slate, hornblende slate, gneiss, and lime rock. Gneiss is the most extensive unit on the map. His map shows many elements of the geologic framework we recognize today. The distribution of his clay slate unit corresponds closely with the Carolina slate and Bel Air belts as we know them now. The gneiss between the two clay slate areas matches the Kiokee belt. Areas of mica slate approximate the northern part of the Kings Mountain belt and the Chauga belt. He also recognized that his talcose slate unit was associated with gold deposits. Granitic and basaltic intrusive rocks are also delineated on the map. It shows the Newberry, Columbia, and Liberty Hill granites we recognize today. Basaltic intrusives outlined include the Bush River of western Newberry County, Dutchmans Creek, Big Wateree Creek, and Ogden gabbros. He described the regional extent of diabase dikes as occuring from Virginia to Alabama, noted their preferred direction and diagrammed their near-vertical orientation. He also referred to the distinctive soil and topography that develops on the large gabbros. Michael Tuomey's report is truly a benchmark publication, for sixty years passed before the next statewide survey was done. Upon completing the report, he left South Carolina to become director of the Alabama Geological Survey.

Southeastern Geology↗
USGS2005

Thermal state and complex geology of a heterogeneous salty crust of Jupiter's satellite, Europa

The complex geology of Europa is evidenced by many tectonic and cryomagmatic resurfacing structures, some of which are "painted" into a more visible expression by exogenic alteration processes acting on the principal endogenic cryopetrology. The surface materials emplaced and affected by this activity are mainly composed of water ice in some areas, but in other places there are other minerals involved. Non-ice minerals are visually recognized by their low albedo and reddish color either when first emplaced or, more likely, after alteration by Europan weathering processes, especially sublimation and alteration by ionizing radiation. While red chromophoric material could be due to endogenic production of solid sulfur allotropes or other compounds, most likely the red substance is an impurity produced by radiation alteration of hydrated sulfate salts or sulphuric acid of mainly internal origin. If the non-ice red materials or their precursors have a source in the satellite interior, and if they are not merely trace contaminants, then they can play an important role in the evolution of the icy crust, including structural differentiation and the internal dynamics. Here we assume that these substances are major components of Europa's cryo/hydrosphere, as some models have predicted they should be. If this is an accurate assumption, then these substances should not be neglected in physical, chemical, and biological models of Europa, even if major uncertainties remain as to the exact identity, abundance, and distribution of the non-ice materials. The physical chemical properties of the ice-associated materials will contribute to the physical state of the crust today and in the geological past. In order to model the influence of them on the thermal state and the geology, we have determined the thermal properties of the hydrated salts. Our new lab data reveal very low thermal conductivities for hydrated salts compared to water ice. Lower conductivities of salty ice would produce steeper thermal gradients than in pure ice. If there are salt-rich layers inside the crust, forming salt beds over the seafloor or a briny eutectic crust, for instance, the high thermal gradients may promote endogenic geological activity. On the seafloor, bedded salt accumulations may exhibit high thermochemical gradients. Metamorphic and magmatic processes and possible niches for thermophilic life at shallow suboceanic depths result from the calculated thermal profiles, even if the ocean is very cold. ?? 2004 Elsevier Inc. All rights reserved.

Icarus↗
USGS1994

Ancient engineering geology projects in China; A canal system in Ganzu province and trenches along the Great Wall in Ningxia Hui Autonomous Region

Two major construction projects of ancient times in China involved what today would be considered engineering geology. We describe an ancient canal system in Gaotai County, Gansu province that was possibly begun in the Han dynasty (206 BC-220 AD). The canal system heads at the Dasha River and extends northwestward for about 55 km to the City of Camels and Xusanwan village. Four parallel canals are present at the local site we examined. The canals were likely built primarily to transport water but may also have served as defensive military barriers. A second project involves trenches and berms along the north side of the Great Wall, clearly part of the Great Wall defensive system. This site is in Ningxia Autonomous Region near the town of Shizuishan. ?? 1994.

Engineering Geology↗
USGS2023

User’s Guide to planetary image analysis and geologic mapping in ArcGIS Pro

Geologic maps are valuable tools in planetary science. Though planetary geologic maps are similar to terrestrial (Earthbased) geologic maps, the nature of planetary exploration introduces unique challenges for geologic mappers. Terrestrial geologic mappers prepare products from field-based observation, often comparing or refining those with aerial and (or) orbital images. Planetary geologic mapping relies almost exclusively on remote observations, which are made by orbiting spacecraft. Therefore, with a few exceptions for locations with rovers, landers, or crewed surface missions, planetary geologic mappers are not able to observe their map area in detail or at smaller scales. As a result, they must interpret and describe their map features differently than those used in terrestrial geologic maps. For example, terrestrial geologic mappers commonly divide units by lithology (rock type) or grain size. However, planetary geologic mappers often do not have detailed enough information to know what type of rock or grain size is present, and instead must divide the planet’s surface into geologic units using differences in tone, color, and surface texture (at multiple scales). Cross-cutting relationships, where apparent, can provide excellent—and often crucial—observations for identifying and subdividing geologic units using orbital datasets. The process of creating planetary maps has evolved over time, from original hand-drawn maps created during the early 1800s through the late 1900s, to the fully digital products created today. Modern-day planetary geologic mapping uses Geographic Information Systems (GIS) software and tools to visualize data, delineate units and landforms, and accurately convey spatial relationships to a map user using cartographic features represented by points, lines, and polygons. This tutorial was written to familiarize both new and experienced planetary geologic mappers with ArcGIS Pro, a commonly used GIS software package developed by Esri. This tutorial introduces new planetary geologic mappers to fundamental concepts and best practices in planetary geologic mapping. For mappers with experience using ArcMap (a previous version of ArcGIS), this tutorial will help to familiarize users with new changes in layout and functionality, so current projects may be migrated into the ArcGIS Pro environment. No prior knowledge is required, although a general familiarity with geology, GIS, and planetary science is recommended. This tutorial includes links to helpful glossaries of common GIS terms and other GIS and planetary science resources in appendix 1. For additional information on planetary geologic mapping, see the U.S Geological Survey (USGS) Astrogeology NASA Planetary Geologic Mapping Program website and the Planetary Mapping Guidelines. Numerous ArcGIS tutorials are also available from Esri’s Tutorials page, through the Esri Academy catalog, and Esri’s ArcGIS Pro Resources page.

Techniques and Methods↗
USGS1994

Cretaceous pollen in Pliocene rocks: Implications for Pliocene climate in the southwestern United States

Pliocene rocks of the Imperial and Palm Spring Formations in southern California contain reworked Cretaceous pollen that helps determine the timing of erosion of Cretaceous rocks on the Colorado Plateau. The stratigraphic distribution of reworked pollen in the Imperial and Palm Spring Formations suggests that erosion of Cretaceous rocks in the southern part of the Colorado Plateau began by 4.5 Ma. Erosion of Cretaceous rocks in the northern part of the plateau began at 3.9 Ma. This erosional history indicates that rapid and extensive erosion of the Colorado Plateau occurred during the Pliocene and supports the hypothesis that much of the Grand Canyon was cut during the Pliocene, rather than earlier in the Tertiary. Rapid erosion and transport from the Colorado Plateau require the climate in that region during the Pliocene to have been significantly wetter than it is today.

Geology↗
USGS2008

Topographic mapping

The U.S. Geological Survey (USGS) produced its first topographic map in 1879, the same year it was established. Today, more than 100 years and millions of map copies later, topographic mapping is still a central activity for the USGS. The topographic map remains an indispensable tool for government, science, industry, and leisure. Much has changed since early topographers traveled the unsettled West and carefully plotted the first USGS maps by hand. Advances in survey techniques, instrumentation, and design and printing technologies, as well as the use of aerial photography and satellite data, have dramatically improved mapping coverage, accuracy, and efficiency. Yet cartography, the art and science of mapping, may never before have undergone change more profound than today.

General Information Product↗
USGS2015

The 3D Elevation Program: summary for New Hampshire

Elevation data are essential to a broad range of applications important to New Hampshire, including flood mitigation, land development, agriculture, transportation planning and design, infrastructure asset inventory and management, and many others. For the State of New Hampshire, elevation data are critical for many business uses such as flood risk management, natural resources conservation, forest resources management, agriculture and precision farming, infrastructure and construction management, and geologic resource assessment and hazard mitigation. Today, high-density light detection and ranging (lidar) data are the primary sources for deriving elevation models and other datasets. Federal, State, Tribal, and local agencies work in partnership to (1) replace data that are older and of lower quality and (2) provide coverage where publicly accessible data do not exist. A joint goal of State and Federal partners is to acquire consistent, statewide coverage to support existing and emerging applications enabled by lidar data. The National Enhanced Elevation Assessment evaluated multiple elevation data acquisition options to determine the optimal data quality and data replacement cycle relative to cost to meet the identified requirements of the user community. The evaluation demonstrated that lidar acquisition at quality level 2 for the conterminous United States and quality level 5 interferometric synthetic aperture radar (ifsar) data for Alaska with a 6- to 10-year acquisition cycle provided the highest benefit/cost ratios. The 3D Elevation Program (3DEP) initiative selected an 8-year acquisition cycle for the respective quality levels. 3DEP, managed by the U.S. Geological Survey, the Office of Management and Budget Circular A–16 lead agency for terrestrial elevation data, responds to the growing need for high-quality topographic data and a wide range of other 3D representations of the Nation’s natural and constructed features.

New Hampshire↗
USGS2014

Ground‐water studies in the Southwest

Geologists are concerned with the rock‐systems that form the crust of the Earth. The groundwater geologists are concerned with the rock‐systems specifically because the open spaces which the rocks contain serve as reservoirs and conduits for water—water which performs a large part of the geologic work that is in progress today and has been in progress during past ages; water which affects profoundly the whole hydrologic cycle and is still the principal source of water‐supply for mankind, as it has been for primitive man and the other land animals before the time of artificial waterworks.

Eos, Transactions, American Geophysical Union↗
USGS2021

U.S. Geological Survey 21st-Century science strategy 2020–2030

Today’s Earth system challenges are far more complex and urgent than those that existed in 1879 when the USGS was established. Society’s greatest challenges are directly or indirectly linked to major areas of USGS science. Increased pressures on natural resources continue with consequences for national security, food and water availability, natural disasters, human health, and biodiversity loss. As we look forward 10, 20, and 30 years, our mission will be more important than ever before. A broad but coherent view is required for stewardship of the Nation’s land, water, mineral, energy, and ecosystem resources, which involves complex tradeoffs among multiple, often competing objectives. Increasingly, resource managers and decision makers need “the whole USGS”: integrated multidisciplinary Earth and biological science data, geospatial tools, predictive models, decision-support tools, and the expertise to interpret them. This Science Strategy defines a vision and mission for how we will continue to evolve USGS Science to address these Earth system challenges.

Circular↗
USGS2025

Shifting baselines of coral-reef species composition from the Late Pleistocene to the present in the Florida Keys

The ongoing global-scale reassembly of modern coral reefs is unprecedented compared with the observed stability of most late Quaternary reef assemblages. One notable exception is the marine isotope stage (MIS) 5e ( ca 130–116 thousand years ago [ka]) reefs in the Florida Keys, where the ubiquitous shallow-water coral, Acropora palmata , was near absent. Little is known, however, about reefs that grew during MIS5d–a ( ca 116–74 ka), between MIS5e and the Holocene. It is therefore unclear whether Florida's unique MIS5e coral assemblages represent a geologically brief anomaly or a more persistent departure from the western Atlantic coral-reef archetype. We addressed that question by reconstructing the composition of MIS5d–a reefs within 29 coral-reef cores collected throughout the Florida Keys. We then compared the relative composition of corals during MIS5d–a to existing datasets from MIS5e, Holocene and modern (1996 and 2022) reefs to evaluate how far today's reef assemblages have diverged from geological baselines. We show that although the proportion of reef frameworks built by corals was remarkably consistent ( ca 38%), species composition changed significantly through time. Acropora palmata was rare throughout MIS5, which we hypothesise was due to greater cold-temperature stress in Florida's subtropical reefs compared with the more climatically stable tropics. In contrast, the massive reef-building coral, Orbicella spp., was regionally dominant throughout the late Quaternary, but has become increasingly rare on modern reefs. By 2022, reefs in the Florida Keys were characterised by a truly novel coral assemblage dominated by Porites astreoides and Siderastrea siderea . In many ways, Florida's reefs defy the concept of a natural baseline; instead, their most persistent characteristic since the Late Pleistocene is their uniqueness. Yet, as reefs are increasingly subjected to unprecedented levels of environmental change, the exceptions to what was normal in the past could, paradoxically, provide the best geological analogues for the future.

Florida↗
USGS1993

Map projections

A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. Every projection has its own set of advantages and disadvantages. There is no "best" projection. The mapmaker must select the one best suited to the needs, reducing distortion of the most important features. Mapmakers and mathematicians have devised almost limitless ways to project the image of the globe onto paper. Scientists at the U. S. Geological Survey have designed projections for their specific needs—such as the Space Oblique Mercator, which allows mapping from satellites with little or no distortion. This document gives the key properties, characteristics, and preferred uses of many historically important projections and of those frequently used by mapmakers today.

General Information Product↗
USGS1995

Sea level change: lessons from the geologic record

Rising sea level is potentially one of the most serious impacts of climatic change. Even a small sea level rise would have serious economic consequences because it would cause extensive damage to the world's coastal regions. Sea level can rise in the future because the ocean surface can expand due to warming and because polar ice sheets and mountain glaciers can melt, increasing the ocean's volume of water. Today, ice caps on Antarctica and Greenland contain 91 and 8 percent of the world's ice, respectively. The world's mountain glaciers together contain only about 1 percent. Melting all this ice would raise sea level about 80 meters. Although this extreme scenario is not expected, geologists know that sea level can rise and fall rapidly due to changing volume of ice on continents. For example, during the last ice age, about 18,000 years ago, continental ice sheets contained more than double the modem volume of ice. As ice sheets melted, sea level rose 2 to 3 meters per century, and possibly faster during certain times. During periods in which global climate was very warm, polar ice was reduced and sea level was higher than today.

Fact Sheet↗
USGS1961

Local evidence of Pleistocene to recent orogeny in the Argentine Andes

Deformed continental sedimentary rocks are exposed in the province of Salta, northwestern Argentina, in one of many intermontane basins of the Puna, a high desert region of subparallel north-trending block-fault ranges. These rocks, formerly thought to be Tertiary but recently dated by fossil diatoms as Pleistocene or younger, comprise several thousand feet of elastics and evaporites interpreted as having accumulated in a structural basin under geologic and climatic conditions much like those of today. They are overlain unconformably by sedimentary rocks and sediments of three distinct depositional periods. The stratigraphic section is as follows: Fan gravels and playa deposits ( Recent ) - Disconformity - Flat-lying lacustrine sandstones and siltstones, minor salines - Angular unconformity - Gently folded conglomerates and sandstones - Angular unconformity - Folded and faulted conglomerate, sandstone, shale, evaporites, and tuffs The basin rocks are folded along north-trending axes and are cut by northeast- to southeast-trending normal faults and by a north-trending reverse fault; the next younger conglomerates and sandstones are gently folded; the two youngest units are undisturbed. The three unconformities, the faults and folds in the older beds, and post-lake-bed faulting of an erosion surface on an adjacent block all indicate intermittent late Pleistocene to Recent local deformation. Neither regional tension nor regional compression can explain both the Pleistocene to Recent movements on the regional block faults and the contemporaneous compressional structures within the basin. The mechanism of horst-wedging, suggested by a current explanation of the analogous ranges of the Great Basin, is proposed as a solution to the dilemma; the horst blocks, forced directly upward along Miocene normal faults, acted as wedges and compressed the sediments accumulating in the graben, creating the pattern of faults and folds now observed. If such structures are ever discovered in the North American Great Basin, as seems reasonable, they should offer new insight into the understanding of basin-and-range structure.

Andes Mountains↗
USGS2017

Long-term trends of surface-water mercury and methylmercury concentrations downstream of historic mining within the Carson River watershed

The Carson River is a vital water resource for local municipalities and migratory birds travelling the Pacific Flyway. Historic mining practices that used mercury (Hg) to extract gold from Comstock Lode ore has left much of the river system heavily contaminated with Hg, a practice that continues in many parts of the world today. Between 1998 and 2013, the United States Geological Survey (USGS) collected and analyzed Carson River water for Hg and methylmercury (MeHg) concentrations resulting in a sixteen year record of unfiltered total mercury (uf.THg), filtered (dissolved) Hg (f.THg), total methylmercury (uf.MeHg), filtered MeHg (f.MeHg), and particulate-bound THg (p.THg) and MeHg (p.MeHg) concentrations. This represents one of the longest continuous records of Hg speciation data for any riverine system, thereby providing a unique opportunity to evaluate long-term trends in concentrations and annual loads. During the period of analysis, uf.THg concentration and load trended downward at rates of −0.85% and −1.8% per year, respectively. Conversely, the f.THg concentration increased at a rate of 1.7% per year between 1998 and 2005, and 4.9% per year between 2005 and 2013. Trends in flow-normalized partition coefficients for both Hg and MeHg suggest a statistically significant shift from the particulate to the filtered phase. The upwardly accelerating f.THg concentration and observed shift from the solid phase to the aqueous phase among the pools of Hg and MeHg within the river water column signals an increased risk of deteriorating ecological conditions in the lower basin with respect to Hg contamination. More broadly, the 16-year trend analysis, completed 140 years after the commencement of major Hg releases to the Carson River, provides a poignant example of the ongoing legacy left behind by gold and silver mining techniques that relied on Hg amalgamation, and a cautionary tale for regions still pursuing the practice in other countries.

Nevada↗
USGS2022

Preliminary geologic map of early Miocene felsic eruptive centers in the Aquarius Mountains, west-central Arizona

The first author, Gary S. Fuis, conducted this mapping in the summer of 1967 in partial fulfillment of the entry requirements into the Ph.D program of the Division of Geological and Planetary Sciences of the California Institute of Technology, Pasadena, Calif. The area mapped lies wholly within the Fort Rock Ranch, a private ranch spanning ~50 square miles in Mohave and Yavapai Counties, Arizona. Access to the ranch is limited, and it is uncertain whether a detailed geologic map of the Aquarius Mountains can be recreated today. Therefore, we are making this map available to the public in this Open-File Report. The original mapping was compiled on an enlarged single aerial photograph at an approximate scale of 1:15,600. The second author, J. Luke Blair, photogrammetrically rectified the original map and added modern topography, which was not available at the time the original map was completed. Modern roads and drainages were also added, including I–40, built after the original map was completed. Both authors reformatted the original map using current USGS geologic map standards.

Arizona↗
USGS1964

Topographic mapping: A challenging future

The United States Geological Survey was established by Congress in 1879 to make a systematic study of the geology and natural resources of the United States. To provide the essential base maps for these studies, the Survey immediately began a program of topographic mapping. In 1882 a general plan was adopted for a standard series of general-purpose topographic maps covering the entire country. Today ... the primary job of the Topographic Division of the Geological Survey is to carry out topographic surveys, and to publish the results as quadrangles in the National Topographic Map Series.

Report↗