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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 847 records · Page 47Linked to original sources
USGS2005

Paleoproterozoic Mojave Province in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of Precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the > or =1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleoproterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States.

Sonora↗
USGS2005

Water-level altitudes in wells completed in the northern segment of the Edwards Aquifer, Travis, Williamson, and Bell Counties, Texas, March-June 2005

During March-June 2005, the U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality (TCEQ), measured water levels in 80 Edwards aquifer wells in the outcrop of the northern segment of the aquifer in Travis, Williamson, and Bell Counties. Public-supply and private wells were selected in areas where outcrop water-level data were sparse. The altitude data can be used in the TCEQ Source Water Assessment and Protection program to help delineate zones of capture around sources of public water supply. Altitudes range from about 490 to about 935 feet above North American Vertical Datum of 1988.

Texas↗
USGS2014

The measurement and computation of flood‐discharge

The Geological Survey has been engaged for more than 50 years in measuring and publishing the discharge of streams of the United States. Measured discharges have ranged in quantity from a small fraction of a second‐foot measured volumetrically to more than 2,000,000 second‐feet measured by use of the current‐meter equipment recently developed by the Survey and described by the writer in the April 1938 issue of Civil Engineering . In this work, systematic and generally complete records of discharge are being obtained at about 3700 gaging‐stations maintained and operated by the United States Geological Survey. A typical structure at which records of river‐stages are obtained is shown in Figure 1. A discharge‐record at a gaging‐station is usually derived from a record of stage by means of a curve or table showing the stage‐discharge relation as determined by measurements of discharge distributed over the range of stage.

Eos, Transactions, American Geophysical Union↗
USGS2022

Earthquake early warning for estimating floor shaking levels of tall buildings

This article investigates methods to improve earthquake early warning (EEW) predictions of shaking levels for residents of tall buildings. In the current U.S. Geological Survey ShakeAlert EEW system, regions far from an epicenter will not receive alerts due to low predicted ground‐shaking intensities. However, residents of tall buildings in those areas may still experience significant shaking due to the acceleration amplification caused by tall buildings’ dynamic behavior, as recently experienced by residents of the 52‐story building in downtown Los Angeles (DTLA) during the 2019 M 7.1 Ridgecrest earthquake. Using more than 400 recorded response data acquired from 77 instrumented buildings in California, here we compare the Federal Emergency Management Agency (FEMA) P‐58 and American Society of Civil Engineers (ASCE) 7‐16 simplified equations for peak floor acceleration (PFA), finding that the ASCE estimation is close to the median of data recorded in large and long‐distance events, whereas the current FEMA estimation is not suitable. In the second part of this article, four instrumented tall buildings in DTLA are extensively studied, and the performance of the simplified and response spectrum (RS) methods giving both an estimation of the free‐field horizontal peak ground acceleration (PGA) and pseudospectral acceleration is evaluated. The results show that the RS method is as accurate as the response history analysis as long as the ground‐motion RS is accurate, whereas the ASCE 7‐16 prediction is conservative. However, when ground‐motion RS or PGA is estimated for DTLA using a ground‐motion model (GMM), the performance of the RS method significantly degrades due to underestimation by the GMM at long periods. The results of this study imply that a nonergodic GMM, which may give more accurate prediction in Los Angeles, could improve the results for PFA when the building’s behavior is dominated by a few long‐period fundamental modes, as is the case for the 52‐story building in DTLA.

California↗
USGS2000

Implications for earthquake risk reduction in the United States from the Kocaeli, Turkey, earthquake of August 17, 1999

This report documents implications for earthquake risk reduction in the U.S. The magnitude 7.4 earthquake caused 17,127 deaths, 43,953 injuries, and displaced more than 250,000 people from their homes. The report warns that similar disasters are possible in the United States where earthquakes of comparable size strike the heart of American urban areas. Another concern described in the report is the delayed emergency response that was caused by the inadequate seismic monitoring system in Turkey, a problem that contrasts sharply with rapid assessment and response to the September Chi-Chi earthquake in Taiwan. Additionally, the experience in Turkey suggests that techniques for forecasting earthquakes may be improving.

Circular↗
USGS2026

Fossil footprints and Ice Age ecosystems of White Sands National Park

Introduction In September 2021, National Park Service staff, U.S. Geological Survey scientists, and an international team of researchers revealed evidence in the form of human footprints at White Sands National Park, New Mexico, that showed people were present in North America between 23,000 and 21,000 years ago. This time was during the Last Glacial Maximum, when large ice sheets covered much of the continent. The results stunned the scientific community and sparked a global debate. The story of how the discoveries were made, how they upended traditional thought, and how they “rewrote the book” on the earliest phases of North American prehistory is a classic example of the process of science.

New Mexico↗
USGS1985

Sequentially and alternatively developed heights for two representative bench marks: near Palmdale, California and along the Bill Williams River, Arizona

This report consists chiefly of 41 tables that both describe and fully document the reconstructions of a series of alternately developed heights based on levelings leading into two representative bench marks in the southwestern United States. One of these marks, 3219, Vincent, California (fig. 1), lies within the area of the Pacific-North American plate boundary; the other, 22Q, Bill Williams River, Arizona (fig. 1), falls within what is believed to be a singularly stable section of southwestern Arizona. Because the levelings that produced these heights were characterized by especially disparate routes with respect to both terrain and climate, the resulting heights provide a test for the existence and magnitude of path-dependent error in geodetic leveling. These two marks were chosen both because of their relative stability with respect to adjacent marks and because their tectonic stability (or instability) can be inferred from the geologic record. Specifically, we can reasonably speculate that 3219 may have sustained measurably significant tectonic displacements during the 20th century, whereas 22Q probably has remained virtually invariant with respect to any fixed datum during the same period. Bench mark 3219 is a standard Geological Survey iron post stamped "3219" near the Southern Pacific Railroad station at Vincent (U.S. Geological Survey, 1898, p. 392); 22Q is a brass cap stamped "22Q (MWD)" set in a concrete post located in a gully immediately north of the Bill Williams River, Arizona (USC&GS Quad. 34114). 3219 was established by the Geological Survey no later than 1897 (Gannett and Baldwin, 1907, p. 365); 22Q was established by the Metropolitan Water District of southern California in advance of the 1931 control surveys along the projected route of the Colorado River Aqueduct.

Arizona, California↗
USGS1997

Assessment of nutrients, suspended sediment, and pesticides in surface water of the upper Snake River basin, Idaho and western Wyoming, water years 1991-95

A water-quality investigation of the upper Snake River Basin began in 1991 as part of the U.S. Geological Survey's National Water- Quality Assessment Program. As part of the investigation, intensive monitoring was conducted during water years 1993 through 1995 to assess surface-water quality in the basin. Sampling and analysis focused on nutrients, suspended sediments, and pesticides because of nationwide interest in these constituents. Concentrations of nutrients and suspended sediment in water samples from 19 sites in the upper Snake River Basin, including nine on the main stem, were assessed. In general, concentrations of nutrients and suspended sediment were smaller in water from the 11 sites upstream from American Falls Reservoir than in water from the 8 sites downstream from the reservoir where effects from land-use activities are most pronounced. Median concentrations of dissolved nitrite plus nitrate as nitrogen at the 19 sites ranged from less than 0.05 to 1.60 milligrams per liter; total phosphorus as phosphorus, less than 0.01 to 0.11 milligrams per liter; and suspended sediment, 4 to 72 milligrams per liter. Concentrations of nutrients and suspended sediment in the main stem of the Snake River, in general, increased downstream. The largest concentrations in the main stem were in the middle reach of the Snake River between Milner Dam and the outlet of the upper Snake River Basin at King Hill. Significant differences (p<0.05) in nutrient and suspended sediment concentrations were noted among groups of sites categorized by the quantity of agricultural land in their upstream drainage basins. Water samples collected from sites in drainage basins where agricultural land constituted less than 10 percent of the land use contained significantly smaller concentrations of nutrients and suspended sediment than samples from sites in drainage basins where agricultural land constituted more than 10 percent of the land use. Significant differences in nutrient and suspended sediment concentrations were inconsistent among groups representing 10 to 19 percent, 20 to 29 percent, and greater than 29 percent agricultural land use. Seasonal concentrations of dissolved nitrite plus nitrate, total phosphorus, and suspended sediment were significantly different among most of the agricultural land-use groups. Concentrations of dissolved nitrite plus nitrate were largest during the nonirrigation season, October through March. Concentrations of total phosphorus and suspended sediment, in general, were largest during high streamflow, April through June. Nutrient and suspended sediment inputs to the middle Snake reach were from a variety of sources. During water year 1995, springs were the primary source of water and total nitrogen to the river and accounted for 66 and 60 percent of the total input, respectively. Isotope and water-table information indicated that the springs derived most of their nitrogen from agricultural activities along the margins of the Snake River. Aquacultural effluent was a major source of ammonia (82 percent), organic nitrogen (30 percent), and total phosphorus (35 percent). Tributary streams were a major source of organic nitrogen (28 percent) and suspended sediment (58 percent). In proportion to its discharge (less than 1 percent), the Twin Falls sewage-treatment plant was a major source of total phosphorus (13 percent). A comparison of discharge and loading in water year 1995 with estimates of instream transport showed a good correlation (relative difference of less than 15 percent) for discharge, total organic nitrogen, dissolved nitrite plus nitrate, total nitrogen, and total phosphorus. Estimates of dissolved ammonia and suspended sediment loads correlated poorly with instream transport; relative differences were about 79 and 61 percent, respectively. The pesticides EPTC, atrazine, desethylatrazine, metolachlor, and alachlor were the most commonly detected in the upper Snake River Basin and accounted for about 75 percent of all pesticide detections. All pesticides detected were at concentrations less than 1 microgram per liter and below water-quality criteria established by the U.S. Environmental Protection Agency. In samples collected from two small agriculturally dominated tributary basins, the largest number and concentrations of pesticides were detected in May and June following early growing season applications. At one of the sites, the pesticide atrazine and its metabolite desethylatrazine were detected throughout the year. On the basis of 37 samples collected basinwide in May and June 1994, total annual subbasin applications and instantaneous instream fluxes of EPTC and atrazine showed logarithmic relations with coefficients of determination (R2 values) of 0.55 and 0.62, respectively. At the time of sampling, the median daily flux of EPTC was about 0.0001 percent of the annual quantity applied, whereas the median daily flux of atrazine was between 0.001 and 0.01 percent.

Idaho;Wyoming↗
USGS1996

Water resources data, Hawaii and other Pacific areas, water year 1989: Volume 2. Guam, Northern Mariana Islands, Federated States of Micronesia, Palau, and American Samoa

Water-resources data for the 1989 water year for other Pacific areas consist of records of discharge, and water quality of streams and stage of a lake and reservoir; water levels and water quality in wells; stage in a tide gage; and rainfall. This report volume 2 contains discharge records for 26 gaging stations; stage only for 2 gaging stations; water quality at 11 gaging stations, one streamflow partial record station, and 54 wells; water levels for 28 observation wells; and tide stages for one tide gage station. Also included are 2 crest-stage partial record stations, 4 miscellaneous partial-record stations, 15 low-flow partial-record stations, and 19 rainfall stations. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating Federal, State, and other agencies in other Pacific areas.

Hawaii↗
USGS2011

Digital surfaces and hydrogeologic data for the Floridan aquifer system in Florida and in parts of Georgia, Alabama, and South Carolina

A digital dataset for the Floridan aquifer system in Florida and in parts of Georgia, Alabama, and South Carolina was developed from selected reports published as part of the Regional Aquifer-System Analysis (RASA) Program of the U.S. Geological Survey (USGS) in the 1980s. These reports contain maps and data depicting the extent and elevation of both time-stratigraphic and hydrogeologic units of which the aquifer system is composed, as well as data on hydrology, meteorology, and aquifer properties. The three primary reports used for this dataset compilation were USGS Professional Paper 1403-B (Miller, 1986), Professional Paper 1403-C (Bush and Johnston, 1988), and USGS Open-File Report 88-86 (Miller, 1988). Paper maps from Professional Papers 1403-B and 1403-C were scanned and georeferenced to the North American Datum of 1927 (NAD27) using the Lambert Conformal Conic projection (standard parallels 33 and 45 degrees, central longitude -96 degrees, central latitude 39 degrees). Once georeferenced, tracing of pertinent line features contained in each image (for example, contours and faults) was facilitated by specialized software using algorithms that automated much of the process. Resulting digital line features were then processed using standard geographic information system (GIS) software to remove artifacts from the digitization process and to verify and update attribute tables. The digitization process for polygonal features (for example, outcrop areas and unit extents) was completed by hand using GIS software.

Alabama, Florida, Georgia, South Carolina↗
USGS2010

Secular variation in economic geology

The temporal pattern of ore deposits on a constantly evolving Earth reflects the complex interplay between the evolving global tectonic regime, episodic mantle plume events, overall changes in global heat flow, atmospheric and oceanic redox states, and even singular impact and glaciation events. Within this framework, a particular ore deposit type will tend to have a time-bound nature. In other words, there are times in Earth history when particular deposit types are absent, times when these deposits are present but scarce, times when they are abundant, and still other times for which we lack sufficient data. Understanding of such secular variation provides a critical first-order tool for exploration targeting, because rocks that have formed or were deformed during a certain time slice may be very permissive for a given deposit type, whereas identification of rocks of less favorable ages would help eliminate large areas during exploration programs. Secular analysis, therefore, is potentially a powerful tool for mineral resource assessment in poorly known terranes, providing a quick filter for favorability of a given deposit type using age of host rocks. Factors bearing on the known age distribution of a particular type of deposit include the following: (1) uneven preservation, (2) data gaps, (3) contingencies of plate motions, and (4) long-term secular changes in the Earth System. The present special issue of Economic Geology is focused on the latter factor, although all of these are interrelated. The selective preservation of certain mineral deposit types and the greater susceptibility for shallowly formed ores in tectonically active environments to be lost to erosion define a pattern that is superimposed on the secular formational trends (e.g., Groves et al., 2005a , b ; Kerrich et al., 2005 ). With improved geochronological methods and the availability of information on important mineral deposits from most parts of the world, data gaps for defining broad temporal distributions of ore types are becoming smaller. It has been increasingly recognized that ore deposit formation is also correlated with plate tectonic setting. Nevertheless, a complex Earth history of supercontinent assembly and breakup has led to the fragmentation of many Paleozoic and Precambrian mineral provinces. The use of plate reconstructions in economic geology, although extremely controversial and conjectural before the late Paleozoic, is critical for defining these provinces prior to the added complications resulting from post-ore plate motions. It is now well established that the temporal patterns of many types of mineral deposits (Fig. 1 1 ) reflect the formation or break-up of supercontinents and the preservation potential of deposits formed during these periods ( Barley and Groves, 1992 ; Titley, 1993 ; Kerrich et al., 2005 ; Goldfarb et al., 2009 ). Approximate time periods for such formation and break-up, respectively, include 2800–2500 and 2450–2100 Ma for Kenorland, 2100–1800 and 1600–1300 Ma for Nuna/Columbia, 1300–1100 and 850–600 Ma for Rodinia, and 600–300 Ma and 200–60 Ma for Gondwanaland-Pangea. A new supercontinent, Amasia, has begun to form during the past 250 m.y., thus overlapping Pangea break-up. Many of the formation-preservation patterns are themselves controlled by progressive cooling of Earth, the change from a mantle-plume buoyancy style to subduction-dominated tectonics, a decreasing buoyancy of the subcontinental lithospheric mantle, and depth of ore formation. In general, orogenic Au, volcanogenic massive sulfide (VMS), epithermal Au-Ag, and porphyry Cu±Au and Mo porphyry deposits form in active margins during periods of supercontinent assembly. Numerous other ore deposit types show an association with supercontinent formation, but develop inland of the active margin. These include many of the MVT Pb-Zn deposits and unconformity-type U deposits. The Tertiary Carlin-type deposits within the deformed shelf sequences along the North American craton margin also appear to have formed during the ongoing growth of Amasia. Those ores associated with periods of supercontinent breakup or attempted breakup are more difficult to define. They probably include diamond, Bushveld-type Ni-Cu-PGE, IOCG, and clastic-dominated Pb-Zn (or SEDEX) deposits in intracontinental areas of failed rifting, and other clastic-dominated Pb-Zn deposits in areas of actual breakup. In all cases, however, these temporal/spatial distributions are ultimately controlled by the secular character of Earth history.

Economic Geology↗
USGS2012

New insights into the nation's carbon storage potential

Carbon sequestration is a method of securing carbon dioxide (CO 2 ) to prevent its release into the atmosphere, where it contributes to global warming as a greenhouse gas. Geologic storage of CO 2 in porous and permeable rocks involves injecting high-pressure CO 2 into a subsurface rock unit that has available pore space. Biologic carbon sequestration refers to both natural and anthropogenic processes by which CO 2 is removed from the atmosphere and stored as carbon in vegetation, soils, and sediments.

Eos, Transactions, American Geophysical Union↗
USGS2006

National workshop on gas hydrates

The range of present knowledge on the subject of gas hydrates and related federal research programs was the topic of discussion at the National Workshop on Gas Hydrates, April 23–24. The intention of the meeting was to provide the impetus for an expanded and broader‐based national research program in both academia and government. Held at the U.S. Geological Survey National Center, Reston, Va., the workshop was organized by Michael D. Max, Naval Research Laboratory, Washington, D.C.; William P. Dillon, USGS, Woods Hole, Mass.; and Rodney D. Malone, U.S. Department of Energy, Morgantown Energy Technology Center, Morgantown, W.Va. The 33 attendees represented academia (33%), federal agencies (58%), and industry (9%).

Eos, Transactions, American Geophysical Union↗
USGS2026

Use of precariously balanced rocks to constrain postglacial earthquake magnitudes in New England, United States

We use the age and fragility of 13 precariously balanced rocks (PBRs) in Massachusetts, New Hampshire, and southwestern Maine to evaluate the estimated probabilistic seismic hazard (PSH) from the U.S. Geological Survey’s National Seismic Hazard Model (NSHM), and also develop a map of maximum postglacial earthquake magnitudes in the region. The PBRs are erratic boulders left behind by the retreat of the Laurentide ice sheet between 13 and 18 ka, and published ice retreat maps are used to estimate their fragility ages. The fragilities and ages of the rocks appear to be consistent with the NSHM, in that the estimated earthquake magnitudes and resulting ground motions that would topple them are only expected on timescales longer than their fragility ages. This result, on the North American passive margin, contrasts with PBR studies at active plate boundaries, where the PBR constraints imply large reductions to estimated PSH. It may be that the PBRs are not old enough in the eastern United States to reveal the same PSH modeling issues as those revealed in the plate boundary settings. The study provides constraints on maximum magnitudes of postglacial earthquakes across much of Massachusetts, New Hampshire, and southwestern Maine, with the constraints limited to the ages of the PBRs.

Maine. Massachusetts, New Hampshire↗
USGS1996

Metamorphism and gold mineralization in the Blue Ridge, southernmost Appalachians

Lode gold mineralization in the Blue Ridge of the southernmost Appalachians is hosted by metavolcanic rocks (e.g., Anna Howe mine, AL; Royal Vindicator mine, GA), metaplutonic rocks (e.g., Hog Mountain mine, AL), and metasedimentary rocks (e.g., Lowe, Tallapoosa, and Jones Vein mines, AL). Most gold occurs in synkinematic quartz + or - plagioclase + or - pyrite + or - pyrrhotite + or - chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages.Mineralogy, chemistry, and O and H isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization. Limited wall-rock alteration in metavolcanic- and metasediment-hosted deposits, and relatively extensive wall-rock alteration in granitoid-hosted deposits, suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks. Stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source, but vary from deposit to deposit (-22 to -47ppm delta D, 4-5ppm, delta 18 O, and 5-7ppm delta 34 S at Anna Howe and Royal Vindicator; -48 to -50ppm delta D, 9-13ppm delta 18 O, and ca. 19ppm delta 34 S at Lowe and Jones Vein; and -22 to -23ppm delta D, 8-11ppm delta 18 O, 9-10ppm delta 34 S, and -6 delta 13 C at Hog Mountain). Silicate mineral thermobarometry of vein, vein selvage, and wall-rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies (480 degrees + or - 75 degrees C at Anna Howe, 535 degrees + or - 50 degrees C at 6.4 + or - 1 kbars at Lowe, 530 degrees + or - 50 degrees C at 6.9 + or - 1 kbars at Tallapoosa, and 460 degrees + or - 50 degrees C at 5.5 + or - 1 kbars at Hog Mountain). Oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry.Auriferous veins contain numerous fluid inclusions that were emplaced in several stages and can be subdivided into five compositional types based on salt and CO 2 concentrations. Fluid inclusion isochores for early formed inclusions from these veins intercept the pressure and temperature conditions estimated from silicate mineral thermobarometry and stable isotope thermometry, and are compatible with entrapment at those conditions. These fluids exhibit significant variation in salinity (X (sub NaCl equiv ) ) = 0.0-0.2) and CO 2 (X (sub CO 2 ) = 0.0-0.2), suggesting variation in fluid-wall-rock interaction that accompanied gold deposition during declining temperatures. Less abundant and later fluids within the veins are dominantly CO 2 .The association of gold mineralization with structurally controlled concordant and discordant quartz sulfide veins, and the temperatures and pressures of wall-rock alteration and regional metamorphism indicate that the present distribution of gold is a result of metamorphism during progressive D 2 -D 3 deformation. Isotopic data for alteration envelopes date this event as Alleghanian: 279 + or - 14 Ma (K-Ar whole rock) and 343 + or - 18 Ma (K-Ar biotite) at Lowe; and 315 + or - 18 Ma (Rb-Sr whole-rock isochron; 87 Sr/ 86 Sr i = 0.7061 + or - 0.0008) and 294 + or - 16 Ma (K-Ar whole-rock) at Hog Mountain. Available data are compatible with development of the lodes during early Alleghanian overthrusting of allochthons over sedimentary rocks of the autochthonous North American margin. The implication is that the fluids were derived from metasedimentary and/or metavolcanic formations in the lower parts of the crystalline thrust stack (or possibly from underlying autochthonous sedimentary formations), ascended along permeable fault zones, and were emplaced as veins into dilatent areas in and adjacent to the fault zones.

Economic Geology↗
USGS2017

Notes on the Archaeology of the Utukok River, Northwestern Alaska

Early in May 1947, a United States Geological Survey field party of five was flown by ski plane to the headwaters of the Utukok River in northwestern Alaska, about 200 miles southwest of Barrow. Three 18–foot canvas boats of a special folding design were taken in along with enough equipment for four months. Food caches had been flown in to six localities on the 200–mile–long river a short time before the group landed. When the “break–up” came late in May the party started down the river working out the geology of the area from a series of 18 camps which were established before reaching the Arctic Ocean in August. During the season 17 archaeological sites were discovered. It is believed that most of these sites are of Eskimo origin and are probably fairly recent. However, an important exception is a well–made Folsom point, announcement of which has been made.

Alaska↗
USGS1969

Our changing continent

Where were the land areas and oceans of the North American Continent one million years ago, compared to our present geography? Was North America always about the same size and shape as it is today? To answer these questions, we must construct maps of the lands and sea that existed during the past ages. This process of reconstructing ancient geography is called paleogeography (from the Greek word "palaios," meaning ancient).

Monograph↗
USGS2025

Four-band image mosaic of the Colorado River Corridor downstream of Glen Canyon Dam in Arizona, derived from the May 2021 airborne image acquisition

In May 2021, the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center acquired airborne multispectral high-resolution data for the Colorado River in the Grand Canyon, Arizona. The image data, which consist of four spectral bands (red, band 1; green, band 2; blue, band 3; and near infrared, band 4) with a ground resolution of 20 centimeters, are available as 16-bit unsigned-integer GeoTIFF files in Sankey and others (2024) (available online at https://doi.org/10.5066/P9BBGN6G ). The image files are projected in the State Plane Coordinate System, using the central Arizona zone (202) with the North American Datum of 1983 National Adjustment of 2011. The assessed spatial accuracy for these data is based on 47 ground-control points that were independent from the ground-control points used by the contractor for aerotriangulation and is reported at the 95-percent confidence level as 0.514 meter (m) and a root mean square error of 0.297 m. The intended uses of this dataset are primarily in support of scientific research and monitoring applications. Examples of these applications include high-resolution spatial and temporal change detection of the river channel, geomorphic landforms, riparian vegetation, and backwater and nearshore habitat, as well as other ecosystem-wide mapping. These imagery data also serve as reference material for field science mission planning, as base data for field data collection including community science activities, and as a highly detailed guide for technical boat operation during science activities such as reconnaissance for nighttime missions and navigating rapids during low flows.

Arizona, Nevada, Utah↗