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At least 631 records · Page 35Linked to original sources
USGS2018

Isostatic gravity map of Mountain Pass and vicinity, California and Nevada

Gravity 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, gravity anomalies can be used to infer subsurface geologic structure, revealing variations in lithology and delineating features such as faults, plutons, volcanic centers, calderas, and deep sedimentary basins. As part of this study, gravity data from more than 2,400 stations were collected and processed to identify lateral changes in subsurface density. Gravity stations were distributed across parts of Shadow Valley, Clark Mountain Range, Mescal Range, Ivanpah Mountains, and Ivanpah Valley. The new gravity data were combined with preexisting gravity data from the surrounding areas in California and Nevada. All gravity data were gridded using a minimum curvature algorithm at an interval of 200 m, and the result is displayed as a color-contour isostatic gravity map.

California, Nevada↗
USGS1952

Preliminary report on the White Canyon area, San Juan county, Utah

The White Canyon area, in the central part of San Juan County, Utah, consists of approximately two 15-minute quadrangles. Approximately 75 square miles have been mapped by the Geological Survey on a scale of 1 inch equals 1 mile, using a combined aerial photography-plane table method. Structure contours were drawn on top of the Organ Rock member of the Cutler formation. Parts of the Gonway and North Point claims, 1/4 mile east of the Happy Jack mine, were mapped in detail. The principal objectives of the investigations were: (1) to establish ore guides; (2) to select areas favorable for exploration; and (3) to map the general geology and to determine the regional relationships of the uranium deposits. The White Canyon area is comprised of sedimentary rocks of Carboniferous to Jurassic age, more than 2,000 feet thick, having a regional dip of 1° to 2° SW. The nearest igneous rocks are in the Henry Mountains about 7 miles west of the northern part of the area; The Shinarump conglomerate of the late Triassic age, the principal ore horizon in the White Canyon area, consists of lenticular beds of sandstone, conglomeratic sandstone, conglomerate, clay, and siltstone. The Shinarump conglomerate, absent in places, is as much as 75 feet thick. The sandstones locally contain molds of logs and fragments of altered volcanic ash. Some of the logs have been replaced by copper and uranium minerals and iron oxides. The clay and siltstone underlie and are interbedded with the sandstone, and are most common in channels that cut into the underlying Moenkopi formation. The Shinarump conglomerate contains reworked Moenkopi siltstone fragments, clay balls, carbonized wood, and pebbles of quarts, quartzite, and chert. Jointing is prominent in the Western part of the mapped area. The three most prominent joint trends are due east, N. 65°-75° W., and N. 65°-75° E. All joints have vertical dips. The red beds are bleached along some joints, especially those that trend N. 65°-75° W. All uranium ore produced has been from the lower part of the Shinarump conglomerate, where it commonly occurs with copper as disseminations and fracture coatings in sandstone. Uranium and copper minerals also occur in low-grade disseminated deposits in the lower Chinle and in the Moenkopi formation and in veins cutting these formations. Although some uranium deposits occur in Chinarump channels and scours, copper and uranium minerals along fractures suggest that channel control may be secondary. Logs and clay balls apparently have exerted some chemical influences for deposition. The uranium occurs as the oxide in some deposits, and as secondary hydrous sulfates, phosphates, oxides, and silicates in these and several other deposits. Charcoal, iron and manganese oxides, and veinlets of hydrocarbon are abnormally radioactive in most of the deposits. Base-metal sulfides are commonly found inside the oxidized zone. Secondary copper minerals include the hydrous sulfates and carbonate. Gangue minerals include quarts, clay minerals, and manganese oxides, dickite (?), calcite, gypsum, pyrite, and chalcedony (?). Principal wall-rock alteration appears to have been silicification, clay alteration, and bleaching. Most of the shipped ore has contained more than 0.3 percent uranium. The ore also contains copper, commonly in grades lower than 1.0 percent. Criteria believed to be most useful for prospecting for concealed uranium deposits are (1) visible uranium minerals; (2) sulfide minerals; (3) secondary copper minerals; (4) dickite (?); (5) hydrocarbons; and (6) bleaching and alteration of the Moenkopi formation.

Utah↗
USGS2012

Carbon export by rivers draining the conterminous United States

Material exports by rivers, particularly carbon exports, provide insight to basin geology, weathering, and ecological processes within the basin. Accurate accounting of those exports is valuable to understanding present, past, and projected basin-wide changes in those processes. We calculated lateral export of inorganic and organic carbon (IC and OC) from rivers draining the conterminous United States using stream gaging and water quality data from more than 100 rivers. Approximately 90% of land area and 80% of water export were included, which enabled a continental-scale estimate using minor extrapolation. Total carbon export was 41–49 Tg C yr −1 . IC was >75% of export and exceeded OC export in every region except the southeastern Atlantic seaboard. The 10 largest rivers, by discharge, accounted for 66% of water export and carried 74 and 62% of IC and OC export, respectively. Watershed carbon yield for the conterminous United States was 4.2 and 1.3 g C m −2 yr −1 for IC and OC, respectively. The dominance of IC export was unexpected but is consistent with geologic models suggesting high weathering rates in the continental United States due to the prevalence of easily weathered sedimentary rock.

Inland Waters↗
USGS1996

Remote mineralogic and lithologic mapping of the Ice River alkaline complex, British Columbia, Canada, using AVIRIS data

The Ice River Alkaline Complex is a late Paleozoic intrusion of mafic alkaline rocks, syenite, and carbonatite exposed in southeastern British Columbia, Canada. The complex intrudes Cambrian and Ordovician shales, slates, and limestones of the Chancellor and Ottertail Formations and the McKay Group. We examined the alkaline complex and adjacent country rocks using Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) data. The data were first calibrated to relative reflectance and then used to spectrally map mineralogies in the study area by using a linear spectral unmixing program. This technique models each pixel spectrum in an AVIRIS image as a linear combination of unique endmember spectra. We selected endmember spectra from well-exposed and spectrally distinct mineralogic units, vegetation, and snow. Four of the endmembers reflect mineralogic variations within the McKay group in the study area, and may represent lateral and vertical variations of sedimentary or metamorphic facies. Otherwise, the resultant spatial distribution of endmembers shows generally close agreement with the published geologic map, although, in several places, our image-map is more accurate than the published map.

Photogrammetric Engineering and Remote Sensing↗
USGS2012

3-D reconstructions of subsurface Pleistocene basalt flows from paleomagnetic inclination data and 40 Ar/ 39 Ar ages in the southern part of the Idaho National Laboratory (INL), Idaho (USA)

The U. S. Geological Survey, in cooperation with the U.S. Department of Energy, is mapping the distribution of basalt flows and sedimentary interbeds at the Idaho National Laboratory in three dimensions to provide data for refining numerical models of groundwater flow and contaminant transport in the eastern Snake River Plain aquifer. Paleomagnetic inclination and polarity data from basalt samples from 47 coreholes are being used to create a three-dimensional (3-D) model of the subsurface of the southern part of the INL. Surface and sub-surface basalt flows can be identified in individual cores and traced in three dimensions on the surface and in the subsurface for distances of more than 20 km using a combination of paleomagnetic, stratigraphic, and 40 Ar/ 39 Ar data. Eastern Snake River Plain olivine tholeiite basalts have K 2 O contents of 0.2 to 1.0 weight per cent. In spite of the low-K content, high-precision 40 Ar/ 39 Ar ages were obtained by applying a protocol that employs short irradiation times (minimizing interferences from Ca derived 36 Ar), frequent measurement of various size atmospheric Ar pipettes to monitor and correct for temporal variation, and signal size dependent nonlinearity in spectrometer mass bias, resulting in age dates with resolution generally between 2 to 10% of the age. 3-D models of subsurface basalt flows are being used to: (1) Estimate eruption volumes; (2) locate the approximate vent areas and extent of sub-surface flows; and (3) Help locate high and low transmissivity zones. Results indicate that large basalt eruptions (>3 km 3 ) occurred at and near the Central Facilities Area between 637 ka and 360 ka; at and near the Radioactive Waste Management Complex before 540 ka; and north of the Naval Reactors Facility at about 580 ka. Since about 360 ka, large basalt flows have erupted along the Arco-Big Southern Butte Volcanic Rift Zone and the Axial Volcanic Zone, and flowed northerly towards the Central Facilities Area. Basalt eruptions shifted the course of the Big Lost River from a more southerly course to its present one.

Idaho↗
USGS2000

Airborne electromagnetics (EM) as a three-dimensional aquifer-mapping tool

The San Pedro River in southeastern Arizona hosts a major migratory bird flyway, and was declared a Riparian Conservation Area by Congress in 1988. Recharge of the adjacent Upper San Pedro Valley aquifer was thought to come primarily from the Huachuca Mountains, but the U. S. Army Garrison of Fort Huachuca and neighboring city of Sierra Vista have been tapping this aquifer for many decades, giving rise to claims that they jointly threatened the integrity of the Riparian Conservation Area. For this reason, the U. S. Army funded two airborne geophysical surveys over the Upper San Pedro Valley (see figure 1), and these have provided us valuable information on the aquifer and the complex basement structure underlying the modern San Pedro Valley. Euler deconvolution performed on the airborne magnetic data has provided a depth-to-basement map that is substantially more complex than a map obtained earlier from gravity data, as would be expected from the higher-resolution magnetic data. However, we found the output of the Euler deconvolution to have "geologic noise" in certain areas, interpreted to be post-Basin-and-Range Tertiary volcanic flows in the sedimentary column above the basement but below the ground surface.

Arizona↗
USGS1987

Passive margins: U.S. Geological Survey Line 19 across the Georges Bank basin

Georges Bank is a shallow part of the Atlantic continental shelf southeast of New England (Emery and Uchupi, 1972, 1984). This bank, however, is merely the upper surface of several sedimentary basins overlying a block-faulted basement of igneous and metamorphic crystalline rock. Sedimentary rock forms a seaward-thickening cover that has accumulated in one main depocenter and several ancillary depressions, adjacent to shallow basement platforms of paleozoic and older crystalline rock. Georges Bank basin contains a thickness of sedimentary rock greater than 10 km, whereas the basement platforms that flank the basin are areas of thin sediment accumulation (less than 5 km).

AAPG Studies in Geology↗
USGS2000

Geologic map of the Snoqualmie Pass 30 x 60 minute quadrangle, Washington

The Snoqualmie Pass quadrangle lies at the north edge of a Tertiary volcanic and sedimentary cover, where the regional structural uplift to the north elevated the older rocks to erosional levels. Much of the quadrangle is underlain by folded Eocene volcanic rocks and fluvial deposts of an extensional event, and these rocks are overlain by Cascade arc volcanic rocks: mildly deformed Oligocene-Miocene rocks and undeformed younger volcanic rocks. Melanges of Paleozoic and Mesozoic rocks are exposed in structural highs in the northern part of the quadrangle. The quadrangle is traversed north to south by the Straight Creek Fault, and the probably partially coincident Darringon-Devils Mountain Fault. A rich Quaternary stratigraphy reveals events of the Frazer glaciation.

IMAP↗
USGS1961

Geology and occurrence of ground water at Jewel Cave National Monument, South Dakota

Jewel Cave National Monument occupies 2 square miles of a broad plateau of sedimentary rocks in western Custer County, S. Dak., and is at an altitude of about 5,400 feet above mean sea level. The sedimentary rocks that constitute the plateau range in age from Cambrian to Pennsylvanian. Rocks of Silurian and Devonian age are absent. The presence of rocks of Ordovician age has not been established definitely but they may be represented by 10 feet of sandstone directly beneath the Englewood limestone of Mississippian age. The sedimentary formations are underlain by schist of Precambrian age. Study of outcrops in the vicinity of the monument confirms the existence of a fault about 1,500 feet north of the entrance to Jewel Cave. The fault trends generally east-west across the monument and has a displacement of about 120 feet about 1 mile west of the entrance to the cave. The effect of the fault on the occurrence of ground water near the cave is not known. In addition to the spring that furnishes the present (1959) water supply for the facilities at Jewel Cave, three springs outside the monument were visited during the study. Combined yield of the 3 springs is less than 2 gpm (gallons per minute). A single test well indicates that the monument at the well site is underlain by 665 feet of limestone, dolomite, and sandstone of Paleozoic age and an undetermined thickness of quartzbiotite schist of Precambrian age. Pumping tests using a cylinder pump indicate that the test well is capable of producing 15 to 18 gpm for a short time from 2 zones of sandstone below the Englewood limestone. These sandstones are believed to present the best possibilities for development of a permanent water supply at the monument.

South Dakota↗
USGS2009

The Eocene-Oligocene sedimentary record in the Chesapeake Bay impact structure: Implications for climate and sea-level changes on the western Atlantic margin

A multidisciplinary investigation of the Eocene-Oligocene transition in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville core from the Chesapeake Bay impact basin was conducted in order to document environmental changes and sequence stratigraphic setting. Planktonic foraminifera and calcareous nannofossil biostratigraphy indicate that the Eyreville core includes an expanded upper Eocene (Biozones E15 to E16 and NP19/20 to NP21, respectively) and a condensed Oligocene-Miocene (NP24-NN1) sedimentary sequence. The Eocene-Oligocene contact corresponds to a =3-Ma-long hiatus. Eocene- Oligocene sedimentation is dominated by great diversity and varying amounts of detrital and authigenic minerals. Four sedimentary intervals are identified by lithology and mineral content: (1) A 30-m-thick, smectite- and illite-rich interval directly overlies the Exmore Formation, suggesting long-term reworking of impact debris within the Chesapeake Bay impact structure. (2) Subsequently, an increase in kaolinite content suggests erosion from soils developed during late Eocene warm and humid climate in agreement with data derived from other Atlantic sites. However, the kaolinite increase may also be explained by change to a predominant sediment input from outside the Chesapeake Bay impact structure caused by progradation of more proximal facies belts during the highstand systems tract of the late Eocene sequence E10.Spectral analysis based on gamma-ray and magnetic susceptibility logs suggests infl uence of 1.2 Ma low-amplitude oscillation of the obliquity period during the late Eocene. (3) During the latest Eocene (Biozones NP21 and E16), several lithological contacts (clay to clayey silt) occur concomitant with a prominent change in the mineralogical composition with illite as a major component: This lithological change starts close to the Biozone NP19/20-NP21 boundary and may correspond to sequence boundary E10-E11 as observed in other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene "precursor isotope event." (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. ?? 2009 The Geological Society of America.

Chesapeake Bay↗
USGS1979

Geology of the south-central part of the New River Mesa Quadrangle, Cave Creek area, Maricopa County, Arizona

A small area north of Cave Creek, Arizona, contains key stratigraphic and structural information bearing on the Cenozoic development of the mountain and desert regions of Arizona. The area contains elements of the two physiographic regions. The northern and western parts are high mesas containing flat lying interbedded Tertiary volcanic and sedimentary strata. These deposits can be traced southward across the physiographic boundary where they are tilted and down faulted into the desert region. Seven bedrock units were revealed by geologic mapping at 1:12,000 scale. They are, in ascending stratigraphic order: (1) a basement of Precambrian schist, granitic rock, and diabase (300 meters exposed), (2) fanglomerate derived from the crystalline rocks, of probable early and middle Oligocene age (0-152 m thick), (3) andesite of possible middle Oligocene age (225 m thick), (4) interbedded sediments and volcanics of Oligocene and Miocene age (30-320 m thick), and (5) resistant cliff forming basalt flows of middle Miocene age (125-180 m thick) that cap the high mesas. Regional uplift of an exposed Precambrian terrane occurred ~38-30 m.y. ago, accompanied by erosion of the basement and deposition of fanglomerate. Regional volcanism began ~30 m.y. ago, apparently with the extrusion of andesite, followed by deposition of alkali basaltic flows, tuff, lake beds, and alluvium in one or more irregularly closed basins, formed as a result of faulting and volcanism. A transition from calcalkali and alkali volcanism to olivine basalt volcanism of the Hickey Formation occurred approximately IS m.y. ago. The interval 14.5-11 m.y. saw the deposition of olivine basalt flows of the New River Mesa formation, which cap the high mesas and correlate with basalt of the Hickey Formation. Topographic development of the mountain-desert region boundary occurred with collapse of the basalts of the New River Mesa formation into the desert region. This may have occurred at the time of initial subsidence of the Verde basin, ~7.5 m.y. ago.

Open-File Report↗
USGS1996

Hydrogeologic terranes and potential yield of water to wells in the Valley and Ridge Physiographic Province in the eastern and southeastern United States

The Valley and Ridge Physiographic Province is underlain by deformed sedimentary rock of Paleozoic age including dolomite, limestone, shale, and sandstone. Regolith (soil, sediment, and weathered rock) covers the Paleozoic rock throughout most of the province. Local differences in lithology, structure, and weathering can result in four orders of magnitude variation in the water-yielding properties of the geologic units that underlie the area. Selected rock types, however, can account for a substantial part of this variation because of the unique way in which these dense, consolidated sedimentary rock types deform and weather to produce secondary openings. On the basis of relations among rock type, water-yielding openings, and water-yielding properties (as indicated by specific capacity), the regolith and consolidated rock were classified and mapped as five hydrogeologic terranes alluvium, dolomite, limestone, argillaceous carbonate rock, and siliciclastic rock. The hydrogeologic terranes are named after the predominant outcrop lithology within them. The western toe of the Blue Ridge Mountains is classified as a subdivision of the dolomite hydrogeologic terrane that may produce yields of water in excess of 1,000 gallons per minute (gal/min) to public and industrial supply wells. Specific-capacity data for homogeneous data sets, which consist of all wells that have the same characteristics in regard to casing diameter, primary use of the water, and topographic setting, revealed significant differences in water-yielding properties among the five hydrogeologic terranes. According to results of Tukey statistical tests at a probability (alpha level) of 0.05, 8 out of 10 pairs of hydrogeologic terranes (for example, alluvium/limestone) had significantly different median specific-capacity values. The median value for public and industrial supply wells in the western toe is three times greater than the value for comparable wells in the dolomite hydrogeologic terrane elsewhere. Estimates of potential yields to public and industrial supply wells were calculated from specific-capacity data for most-productive wells, which have casing diameter of 7 in. or more, discharge water primarily for public or industrial supply, and are in a valley. Median constant drawdowns, calculated from reported drawdowns, were assumed to be between 10 and 90 ft for wells completed in each of the five hydrogeologic terranes, and well-entrance losses were assumed to be negligible. Estimated interquartile ranges in potential yields to 412 mostproductive wells in the five hydrogeologic terranes were 170 to 580 gal/min, alluvium; 210 to 1,400 gal/min, dolomite; 80 to 720 gal/min, limestone; 65 to 850 gal/min, argillaceous carbonate rock; and 70 to 280 gal/min, siliciclastic rock.

Alabama, Georgia, Maryland, New Jersey, Pennsylvan↗
USGS2007

Three-dimensional geologic model of the northern Nevada rift and the Beowawe geothermal system, north-central Nevada

A three-dimensional (3D) geologic model of part of the northern Nevada rift encompassing the Beowawe geothermal system was developed from a series of two-dimensional (2D) geologic and geophysical models. The 3D model was constrained by local geophysical, geologic, and drill-hole information and integrates geologic and tectonic interpretations for the region. It places important geologic constraints on the extent and configuration of the active Beowawe geothermal system. The geologic framework represented in this model facilitates hydrologic modeling of the Beowawe geothermal system and evaluation of fluid flow in faults and adjacent rock units. Basin depths were determined using an iterative gravity-inversion technique that calculates the thickness of low-density, basin-filling deposits. The remaining subsurface structure was modeled using 2D potential-field modeling software. Crustal cross sections from the 2D models were generalized for use in the 3D model and consist of six stratigraphic layers defined as low-density basin sediments, volcanic rocks, basalt-andesite rocks of the northern Nevada rift, Jurassic and Cretaceous intrusive rocks, and Paleozoic siliceous and carbonate sedimentary rocks of the upper and lower plates of the Roberts Mountains allochthon, respectively. This simplified stratigraphy was combined with mapped surface geology and was extrapolated across the 3D model area. Features along the northern Nevada rift depicted by the model may represent preexisting crustal structures that controlled the locations and character of Tertiary tectonic and magmatic events related to Basin and Range extension and emplacement of the middle Miocene northern Nevada rift. Several of the geologic features represented are important components of the Beowawe geothermal system. Prominent ENE-trending faults (e.g., Malpais fault) that bound the southern edge of Whirlwind Valley, and older NNW-striking faults (e.g., Dunphy Pass and Muleshoe faults) that form major features of the model, are likely important pathways for geothermal fluids and groundwater flow from the Humboldt River, which may recharge the Beowawe system.

Nevada↗
USGS1991

Geologic map and profiles of the north wall of the Snake River Canyon, Thousand Springs and Niagara quadrangles, Idaho

The Snake River Plain is a broad, arcuate region of low relief that extends more than 300 mi across southern Idaho. The Snake River enters the plain near Idaho Falls and flows westward along the southern margin of the eastern Snake River Plain (fig. 1), a position mainly determined by the basaltic lava flows that erupted near the axis of the plain. The highly productive Snake River Plain aquifer north of the Snake River underlies most of the eastern plain. The aquifer is composed of basaltic rocks that are interbedded with fluvial and lacustrine sedimentary rocks. The top of the aquifer (water table) is typically less than 500 ft below the land surface but is deeper than 1,000 ft in a few areas. The Snake River has excavated a canyon into the nearly flat lying basaltic and sedimentary rocks of the eastern Snake River Plain aquifer, which discharges from the northern canyon wall as springs of variable size, spacing, and altitude. Geologic controls on springs are of importance because nearly 60 percent of the aquifer's discharge occurs as spring flow along the describes the geologic occurrence of springs along the northern wall of the Snake River canyon. This report is one of several that describes the geologic occurrence of springs along the northern wall of the Snake River canyon from Milner Dam to King Hill. To understand the local geologic controls on springs, the Water Resources Division of the U.S. Geological Survey initiated a geologic mapping project as part of their Snake River Plain Regional Aquifer System-Analysis Program. Objectives of the project were (1) to prepare a geologic map of a strip of land immediately north of the Snake River canyon, (2) to map the geology of the north canyon wall in profile, (3) to locate spring occurrences along the north side of the Snake River between Milner Sam and King Hill, and (4) to estimate spring discharge from the north wall of the canyon.

Idaho↗
USGS2022

Advancing geophysical techniques to image a stratigraphic hydrothermal resource

Sedimentary-hosted geothermal energy systems are permeable structural, structural-stratigraphic, and/or stratigraphic horizons with sufficient temperature for direct use and/or electricity generation. Sedimentary-hosted (i.e., stratigraphic) geothermal reservoirs may be present in multiple locations across the central and eastern Great Basin of the USA, thereby constituting a potentially large base of untapped, economically accessible energy resources. Sandia National Laboratories has partnered with a multi-disciplinary group of collaborators to evaluate a stratigraphic system in Steptoe Valley, Nevada using both established and novel geophysical imaging techniques. The goal of this study is to inform an optimized strategy for subsequent exploration and development of this and analogous resources. Building from prior Nevada Play Fairway Analysis (PFA), this team is primarily 1) collecting additional geophysical data, 2) employing novel joint geophysical inversion/modeling techniques to update existing 3D geologic models, and 3) integrating the geophysical results to produce a working, geologically constrained thermo-hydrological reservoir model. Prior PFA work highlights Steptoe Valley as a favorable resource basin that likely has both sedimentary and hydrothermal characteristics. However, there remains significant uncertainty on the nature and architecture of the resource(s) at depth, which increases the risk in exploratory drilling. Newly acquired gravity, magnetic, magnetotelluric, and controlled-source electromagnetic data, in conjunction with new and preceding geoscientific measurements and observations, are being integrated and evaluated in this study for efficacy in understanding stratigraphic geothermal resources and mitigating exploration risk. Furthermore, the influence of hydrothermal activity on sedimentary-hosted reservoirs in favorable structural settings (i.e., whether fault-controlled systems may locally enhance temperature and permeability in some deep stratigraphic reservoirs) will also be evaluated. This paper provides details and current updates on the course of this study in-progress.

Geothermal Resources Council Transactions↗
USGS1989

Sedimentary framework of the southern Maine inner continental shelf: Influence of glaciation and sea-level change

Although the tidally influenced shoreline of Maine is longer than that of virtually any other state, almost no research on its geology has been published. In order to go some way towards remedying this, 1500 km of high-resolution seismic reflection data and 800 km of sidescan sonar imagery have been collected. On the basis of these data and observations made during ten submersible dives, more than 800 bottom samples were collected and evaluated for texture and composition. The understanding of the sedimentary framework of the southern Maine shelf and the processes that maintain it are summarized, and future research directions to evaluate the strategic mineral potential are indicated. In the past 14,000 years, the Maine shelf has experienced a deglaciation and two marine transgressions separated by a regression. The deglaciation was accompanied by the first transgression and deposited till interbedded with up to 40 m of glaciomarine sediment (the Presumpscot Formation) across the shelf. The first transgression culminated about 12,500 yrs B.P., and its landward limit is marked by large glaciomarine deltas 50-100 km landward of the present-day coast. Sea level fell until about 9500 yrs B.P., when shorelines were cut at about the 65 m depth and some large "lowstand deltas" were deposited. Sea level has risen since then and in the general absence of modern river sediment input marine processes have reworked the older sediment. Five shelf environments have been defined in terms of their surficial sediment and stratigraphy. Nearshore ramps are sandy regions extending to about 30 m deep offshore of sandy beaches. These may be reworked lowstand deltas, and possess the thickest bodies of sand in the region. Nearshore basins are mud-filled troughs seaward of coastal areas lacking significant river input. Slumping glaciomarine deposits provide most of the Holocene mud that floors these basins. Rocky zones are extensive areas of exposed rock most common in the 30-50 m depth range. These are areas of high carbonate productivity and provide shell fragments to adjacent areas. The outer basins are muddy regions that begin at the 65 m shoreline and extend beyond the 100 m isobath to the deep Gulf of Maine. Finally, shelf valleys are former stream courses that connect nearshore ramps and basins to the outer basins. These bedrock-framed valleys are filled with sand and mud and are apparently still active conduits for the offshore movement of sediment. The mineralogy of the shelf sediment is complex, and it is not yet clear whether glacial homogenization has obliterated distinctions between river drainage basins and the adjacent shelf. Studies are continuing into northern Maine and analysis of the heavy mineralogy of the shelf sediment utilizing a 2 m Humphrey Spiral to process large grab samples and cores has begun. ?? 1989.

Marine Geology↗
USGS2012

Surficial geologic map of the Cuddeback Lake 30' x 60' quadrangle, San Bernardino and Kern Counties, California

The 1:100,000-scale Cuddeback Lake quadrangle is located in the western Mojave Desert north-northeast of Los Angeles, between the southern Sierra Nevada and San Bernardino Mountains, in Kern and San Bernardino Counties, California. Geomorphic features include high-relief mountains, small hills, volcanic domes, pediments, broad alluvial valleys, and dry lakes. It is one in a series of surficial geologic maps created to investigate landscape development and tectonic evolution of the northern Mojave Desert. The mapped area includes pre-Tertiary plutonic, metavolcanic, metasedimentary, and igneous rocks; Tertiary sedimentary and volcanic rocks; and Quaternary sediments and basalts. The map area includes the El Paso, Lockhart, Blackwater, and Muroc Faults, as well as the central segment of the Garlock Fault Zone. The tectonically active western Mojave Desert and the variety of surficial materials have resulted in distinctive geomorphic features and terrains. Geologic mapping shows that active faults are widespread and have diverted drainage patterns. The tectonically active area near the Garlock Fault Zone and the nearby El Paso Fault influenced development of drainage networks; base level is controlled by fault offset. Evidence of a late Tertiary drainage network is preserved in remnants of alluvial fans and paleodrainage deposits north of the El Paso Mountains, west of the Lava Mountains, and south and west of the Rand Mountains. Holocene fault activity for the Cantil Valley, Lockhart, Garlock, and Rand Mountain Faults is indicated by displaced stream channels, playa-filled depressions, scarps, and shutter ridges. Previously unmapped Holocene and Late Pleistocene fault strands identified near the Rand Mountains may represent a splay at the northwest termination of the Lockhart Fault. The Grass Valley Fault, northwest of Black Mountain, is a right-lateral, strike-slip fault that may be a splay of the Blackwater Fault. Holocene activity on the Grass Valley Fault is indicated by one displaced early Holocene stream terrace. Mapped faults in Fremont Valley are tentatively identified as surficial expressions of the buried Cantil Valley Fault.

California↗
USGS2026

Understanding the resource potential of natural hydrogen on Earth: Scientific gaps, uncertainties and recommendations

A comprehensive scientific research roadmap is essential to bridge knowledge gaps and deepen the understanding of key geological, geochemical, and geophysical aspects of natural hydrogen (H 2 ) as a potential new energy resource. This paper reviews major scientific uncertainties on natural H 2 , suggesting research priorities, as a guide for defining exploration strategies, techniques, and data interpretation. The uncertainties concern all phases of the natural H 2 cycle, from generation (source rocks) through migration (advection and diffusion) and accumulation (reservoir and cap rocks) to the application and interpretation of subsurface and surface geochemical and geophysical exploration techniques. Understanding H 2 sources and generation rates (the amount of H 2 generated by a given volume of rock over time) is crucial for determining whether a geological H 2 system operates as a short-term dynamic system with rapid H 2 production and release, or as a conventional gas system with long-term accumulations, analogous to petroleum reservoirs. Preliminary estimates for serpentinisation, radiolysis, and organic matter degradation suggest that H 2 generation is not inherently fast, especially for non-hydrothermal continental systems (crystalline basement of shields, ophiolites, peridotite massifs, sedimentary basins), and long-term accumulations, like those of fossil natural gas systems, represent the most likely scenario. The mechanisms of H 2 migration through geological formations require application of fundamental principles of fluid-flow physics, distinguishing advection and diffusion, as well as their forms (from gas-phase, bubble flows to aqueous solutions). Additional studies of H 2 accumulation and retention in subsurface reservoirs could improve understanding of mechanisms of H 2 migration by focusing on the rock fluid-bearing properties and the factors affecting H 2 preservation, such as the presence of cap rocks impermeable to H 2 , pressure conditions, residence times, and microbial or abiotic consumption. Advanced techniques, including reservoir modelling, flow simulations, 3D imaging (micro-CT) of H 2 -bearing rocks, and extraction and analysis of gas occluded in rocks, can provide insights into the stability and potential recoverability of H 2 accumulations. The interpretation of surface exploration techniques, including gas geochemistry, geophysics, and remote sensing, long employed in mineral and energy resource exploration, is now being adapted for natural H 2 studies, but challenges remain in the data interpretation. Distinguishing H 2 seepage due to geological degassing from H 2 produced near the surface by modern microbial processes or artificial sources, such as hammering or drilling for soil-gas sampling, drilling into aquifers, and corrosion in boreholes, is an essential step in exploration. The simple detection of H 2 in soils, even in morphological structures like sub-circular depressions or “fairy circles”, cannot be cursorily interpreted as a signal of natural H 2 seepage from a deep source. A holistic geochemical approach, including isotopic analyses of gases associated with H 2 , is recommended to distinguish among the variety of possible H 2 origins. Observations of H 2 in wells should be interrogated to rule out possible artifacts such as corrosion and drill bit metamorphism. The integration of multiple geophysical methods, including seismic, gravimetric, magnetic, and electro-magnetic surveys, is recommended to mitigate interpretation ambiguities regarding the structure of a subsurface H 2 system (source and reservoir rocks, including fluid and gas storage), due to the non-uniqueness of rock-specific physical properties.

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