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At least 739 records · Page 41Linked to original sources
USGS2002

Subsurface and petroleum geology of the southwestern Santa Clara Valley ("Silicon Valley"), California

Gravity anomalies, historical records of exploratory oil wells and oil seeps, new organic-geochemical results, and new stratigraphic and structural data indicate the presence of a concealed, oil-bearing sedimentary basin beneath a highly urbanized part of the Santa Clara Valley, Calif. A conspicuous isostatic-gravity low that extends about 35 km from Palo Alto southeastward to near Los Gatos reflects an asymmetric, northwest-trending sedimentary basin comprising low-density strata, principally of Miocene age, that rest on higher-density rocks of Mesozoic and Paleogene(?) age. Both gravity and well data show that the low-density rocks thin gradually to the northeast over a distance of about 10 km. The thickest (approx 4 km thick) accumulation of low-density material occurs along the basin's steep southwestern margin, which may be controlled by buried, northeast-dipping normal faults that were active during the Miocene. Movement along these hypothetical normal faults may been contemporaneous (approx 17–14 Ma) with sedimentation and local dacitic and basaltic volcanism, possibly in response to crustal extension related to passage of the northwestward-migrating Mendocino triple junction. During the Pliocene and Quaternary, the normal faults and Miocene strata were overridden by Mesozoic rocks, including the Franciscan Complex, along northeastward-vergent reverse and thrust faults of the Berrocal, Shannon, and Monte Vista Fault zones. Movement along these fault zones was accompanied by folding and tilting of strata as young as Quaternary and by uplift of the modern Santa Cruz Mountains; the fault zones remain seismically active. We attribute the Pliocene and Quaternary reverse and thrust faulting, folding, and uplift to compression caused by local San Andreas Fault tectonics and regional transpression along the Pacific-North American Plate boundary. Near the southwestern margin of the Santa Clara Valley, as many as 20 exploratory oil wells were drilled between 1891 and 1929 to total depths as great as 840 m. At least one pump unit is still standing. Although no lithologic or paleontologic samples are available from the wells, driller's logs indicate the presence of thick intervals of brown shale and sandstone resembling nearby outcrops of the Miocene Monterey Formation. Small amounts of oil and gas were observed in several wells, but commercial production was never established. Oil from the Peck well in Los Gatos is highly biodegraded, contains biomarkers commonly found in oils derived from the Monterey Formation, and has a stable-C-isotopic (d13C) composition of –23.32 permil, indicating derivation from a Miocene Monterey Formation source rock. Preliminary calculations suggest that about 1 billion barrels of oil may have been generated from source rocks within the Monterey Formation in the deepest part of the subsurface sedimentary basin between Los Gatos and Cupertino. Most of this oil was probably lost to biodegradation, oxidation, and leakage to the surface, but some oil may have accumulated in as-yet-undiscovered structural and stratigraphic traps along the complex structural boundary between the Santa Clara Valley and the Santa Cruz Mountains. Although some of these undiscovered accumulations of oil may be of commercial size, future petroleum exploration is unlikely because most of the area is currently devoted to residential, recreational, commercial, and industrial uses.

California↗
USGS1962

Lake Bonneville: Geology of southern Cache Valley, Utah

This report, covering about 450 square miles in southern Cache Vally, Utah, is one of a series dealing with the geology of Pleistocene Lake Bonneville. The report summarizes in tabular form the Paleozoic formations that are exposed in the mountains adjacent to Cache Valley and describes briefly the Tertiary formations—the Wasatch and Salt Lake formations— which are exposed in the valley. Most of the report deals with the Quaternary deposits. Fan gravel and landslides of pre-Lake Bonneville Quaternary age are exposed in a few places at the edges of the basin, and well logs indicate a deep fill of this age in the subsurface of the basin interior. The sediments of Lake Bonneville comprise the Lake Bonneville group. The oldest of the unconsolidated deposits are the Alpine and Bonneville formations, which were mostly mapped together in southern Cache Valley. These formations are composed mostly of silt, but they include some gravel in embankments and small deltas. Their thickness ranges from about 50 to 100 feet. Overlying the Alpine and Bonneville formations is the Provo formation 50 to 75 feet thick. In Cache Valley, as elsewhere in the Lake Bonneville basin, the Provo includes extensive gravel deposits in bars, spits, and deltas. It is the surface formation in much of Cache Valley. Deposits younger than the Provo, mostly of Recent age, include alluvial flans, flood-plain alluvium, natural levee deposits along the Bear River, slope wash, eolian sand, and cones of spring tufa. Several faults, active in Tertiary time, are mapped. Well logs indicate that the pre-Lake Bonneville deposits of Quaternary age are surprisingly thin in Cache Valley, suggesting that the valley had exterior drainage during most of Pleistocene time. The logs show two main aquifers of gravel and sand— the upper one between the Provo formation and the Alpine and Bonneville formations and the other directly beneath the Alpine and Bonneville deposits. These aquifers probably are alluvium deposited during interlake intervals. The shore embankments and deltas of the Lake Bonneville group are abundant sources of gravel and sand for construction. Much of the gravel is suitable for concrete aggregate.

Utah↗
USGS2005

Geologic and geophysical maps of the Las Vegas 30' x 60' quadrangle, Clark and Nye counties, Nevada, and Inyo County, California

Las Vegas and Pahrump are two of the fastest growing cities in the US, and the shortage of water looms as among the greatest future problems for these cities. These new maps of the Las Vegas 30 x 60-minute quadrangle provide a geologic and geophysical framework and fundamental earth science database needed to address societal issues such as ground water supply and contamination, surface flood, landslide, and seismic hazards, and soil properties and their changing impact by and on urbanization. The mountain ranges surrounding Las Vegas and Pahrump consist of Mesozoic, Paleozoic and Proterozoic rocks. A majority of these rocks are Paleozoic carbonate rocks that are part of Nevada's carbonate rock aquifer province. The Spring Mountains represent a major recharge site in the province, where maximum altitude is 3,632 m (Charleston Peak) above sea level. Rocks in the Sheep and Las Vegas Ranges and Spring Mountains contain correlative, northeast-striking, southeast-verging thrust faults that are part of the Cretaceous, Sevier orogenic belt. These thrusts were offset during the Miocene by the Las Vegas Valley shear system (LVVSZ). We conducted new mapping in the Blue Diamond area, highlighting refined work on the Bird Spring thrust, newly studied ancient landslides, and gravity-slide blocks. We conducted new mapping in the Las Vegas Range and mapped previously unrecognized structures such as the Valley thrust and fold belt; recognition of these structures has led to a refined correlation of Mesozoic thrust faults across the LVVSZ. New contributions in the quadrangle also include a greatly refined stratigraphy of Paleozoic bedrock units based on conodont biostragraphy. We collected over 200 conodont samples in the quadrangle and established stratigraphic reference sections used to correlate units across the major Mesozoic thrust faults. Quaternary deposits cover about half of the map area and underlie most of the present urbanized area. Deposits consist of large coalescing alluvial fans that grade downslope to extensive areas of fine-grained sediment indicative of groundwater-discharge during the Pleistocene. In the central areas of Las Vegas and Pahrump valleys, Quaternary fault scarps associated with past ground-water discharge deposits suggest a genetic relationship. In collaboration with NBMG and University of Nevada, a variety of ages of gravelly alluvium are newly mapped using surficial characteristics and soil development, along with reassessment of previously published mapping during compilation. Reconnaissance geochronology (thermoluminescence and U-series) of eolian and authigenic components of surficial and buried soils and spring deposits is applied to test hypotheses of geomorphic and hydrologic response to climate change over the past 100 k.y.). The major structure in the Las Vegas quadrangle is the LVVSZ. Because the LVVSZ is concealed by thick basin-fill deposits of Quaternary and Tertiary age, it was characterized primarily based on geophysics. Likewise, the newly described State line fault system in Pahrump Valley has also been characterized by geophysics, where geophysically inferred structures correlate remarkably with surface structures defined by our new geologic mapping in the Mound Spring and Hidden Hills Ranch 7.5-minute quadrangles.

Scientific Investigations Map↗
USGS2013

Reconnaissance geologic map of the Kuskokwim Bay region, southwest Alaska

The rocks of the map area range from Proterozoic age metamorphic rocks of the Kanektok metamorphic complex (Kilbuck terrane) to Quaternary age mafic volcanic rocks of Nunivak Island. The map area encompasses much of the type area of the Togiak-Tikchik Complex. The geologic maps used to construct this compilation were, for the most part, reconnaissance studies done in the time period from the 1950s to 1990s. Pioneering work in the map area by J.M. Hoare and W.L. Coonrad forms the basis for much of this map, either directly or as the stepping off point for later studies compiled here. Physiographically, the map area ranges from glaciated mountains, as much as 1,500 m high, in the Ahklun Mountains to the coastal lowlands of northern Bristol Bay and the Kuskokwim River delta. The mountains and the finger lakes (drowned fiords) on the east have been strongly affected by Pleistocene and Holocene glaciation. Within the map area are a number of major faults. The Togiak-Tikchik Fault and its extension to the northeast, the Holitna Fault, are considered extensions of the Denali fault system of central Alaska. Other sub-parallel faults include the Golden Gate, Sawpit, Goodnews, and East Kulukak Faults. Northwest-trending strike-slip faults crosscut and offset northeast-trending fault systems. Rocks of the area are assigned to a number of distinctive lithologic packages. Most distinctive among these packages are the high-grade metamorphic rocks of the Kanektok metamorphic complex or Kilbuck terrane, composed of a high-grade metamorphic orthogneiss core surrounded by greenschist and amphibolite facies schist, gneiss, and rare marble and quartzite. These rocks have yielded radiometric ages strongly suggestive of a 2.05 Ga emplacement age. Poorly known Paleozoic rocks, including Ordovician to Devonian and Permian limestone, are found east of the Kanektok metamorphic complex. A Triassic(?) ophiolite complex is on the southeast side of Kuskokwim Bay; otherwise only minor Triassic rock units are known. The most widespread rocks of the area are Jurassic and Early Cretaceous(?) volcanic and volcaniclastic rocks. The Kuskokwim Group flysch is restricted largely to the northeast part of the map area. It consists primarily of shelf and minor nearshore facies rocks. Primarily exposed in the lowlands west of the Ahklun Mountains, extensive latest Tertiary and Quaternary alkalic basalt flows and lesser pyroclastic rocks form much of the bedrock of the remaining area. On Saint Matthew Island, Cretaceous volcanic and pyroclastic rocks occur that are not found elsewhere within the map area. The Kuskokwim Group and older rocks, including on Saint Matthew Island, but not the Kanektok metamorphic complex, are intruded by widely dispersed Late Cretaceous and (or) Early Tertiary granitic rocks. Much of the lowland area is mantled by unconsolidated deposits that include glacial, alluvial and fluvial, marine, estuarine, and eolian deposits. These formed during several episodes of Quaternary glaciation.

Alaska↗
USGS2011

Geologic map of the Bailey 30' x 60' quadrangle, North-Central Colorado

The Bailey, Colo. 1:100,000-scale quadrangle lies within two physiographic and geologic provinces in central Colorado: 1) the Front Range and 2) South Park. Most of the Front Range is composed of Proterozoic rocks ranging in age from 1,790 Ma to 1,074 Ma. Along the eastern flanks and within the Denver Basin, sedimentary rocks ranging from Pennsylvanian to Cretaceous are deformed and steeply tilted to the east. Upper Cretaceous through Paleocene rocks were deposited in the foreland (that is, the Front Range eastern flank) and hinterland (that is, South Park) of this thrust and reverse fault system developed during the Late Cretaceous to Paleocene Laramide orogeny. Within South Park, rocks range in age from Pennsylvanian to Miocene with Quaternary deposits indicating tectonic subsidence of the basin. These rocks record five major geologic episodes: 1) the Paleozoic Anasazi uplift that formed the Ancestral Rockies, 2) the Late Cretaceous to Paleocene Laramide orogeny, 3) widespread Eocene to Oligocene volcanism, 4) Oligocene-Quaternary tectonics, and 5) Quaternary glacial episodes.

Colorado↗
USGS2020

Geologic map of Petroglyph National Monument and vicinity, Bernalillo County, New Mexico

This geologic map depicts and briefly describes geologic units underlying Petroglyph National Monument and immediately adjacent areas in Bernalillo County, New Mexico. The Monument is underlain dominantly by Quaternary basalts of the Albuquerque Volcanoes volcanic field, a series of basin-filling volcanic flows and associated vents from a monogenetic volcanic highland along the eastern margin of the Llano de Albuquerque. This compilation builds on data of previously published geologic maps and reports but includes new interpretive synthesis of volcanic stratigraphy and a unified representation of Quaternary surficial deposits overlying volcanic deposits within the Monument and areas immediately adjacent. This geologic map emphasizes the distribution of Quaternary volcanic vent areas and lava flow deposits which were incompletely mapped on previous publications. Surficial deposits are simplified, but uniformly mapped and described in contrast to varying map unit distributions, names and descriptions presented in the references above. Underlying deposits of the upper Santa Fe Group are exposed in the western part of the map area and described briefly. North-trending, syn- and post-eruption faulting is well preserved in the volcanic field and reflected in the subsurface models of aeromagnetic data. These faults are dominated by dip-slip displacement and are interpreted as extensional faults of the central Albuquerque Basin of the northern Rio Grande rift. Elongate distribution of vents for most of the volcanic deposits are spatially associated with the easternmost of these faults and are interpreted to reflect eruptions from fissures paralleling the regional extensional fault trends of the rift.

New Mexico↗
USGS2007

The Black Mountain tectonic zone--a reactivated northeast-trending crustal shear zone in the Yukon-Tanana Upland of east-central Alaska: Chapter D in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

The Black Mountain tectonic zone in the YukonTanana terrane of east-central Alaska is a belt of diverse northeast-trending geologic features that can been traced across Black Mountain in the southeast corner of the Big Delta 1°×3° degree quadrangle. Geologic mapping in the larger scale B1 quadrangle of the Big Delta quadrangle, in which Black Mountain is the principal physiographic feature, has revealed a continuous zone of normal and left-lateral strikeslip high-angle faults and shear zones, some of which have late Tertiary to Quaternary displacement histories. The tectonic zone includes complexly intruded wall rocks and intermingled apophyses of the contiguous mid-Cretaceous Goodpaster and Mount Harper granodioritic plutons, mafic to intermediate composite dike swarms, precious metal mineralization, early Tertiary volcanic activity and Quaternary fault scarps. These structures define a zone as much as 6 to 13 kilometers (km) wide and more than 40 km long that can be traced diagonally across the B1 quadrangle into the adjacent Eagle 1°×3° quadrangle to the east. Recurrent activity along the tectonic zone, from at least mid-Cretaceous to Quaternary, suggests the presence of a buried, fundamental tectonic feature beneath the zone that has influenced the tectonic development of this part of the Yukon-Tanana terrane. The tectonic zone, centered on Black Mountain, lies directly above a profound northeast-trending aeromagnetic anomaly between the Denali and Tintina fault systems. The anomaly separates moderate to strongly magnetic terrane on the northwest from a huge, weakly magnetic terrane on the southeast. The tectonic zone is parallel to the similarly oriented left-lateral, strike-slip Shaw Creek fault zone 85 km to the west.

Alaska;Yukon↗
USGS2012

Groundwater quality in West Virginia, 1993-2008

Approximately 42 percent of all West Virginians rely on groundwater for their domestic water supply. However, prior to 2008, the quality of the West Virginia’s groundwater resource was largely unknown. The need for a statewide assessment of groundwater quality prompted the U.S. Geological Survey (USGS), in cooperation with West Virginia Department of Environmental Protection (WVDEP), Division of Water and Waste Management, to develop an ambient groundwater-quality monitoring program. The USGS West Virginia Water Science Center sampled 300 wells, of which 80 percent were public-supply wells, over a 10-year period, 1999–2008. Sites for this statewide ambient groundwater-quality monitoring program were selected to provide wide areal coverage and to represent a variety of environmental settings. The resulting 300 samples were supplemented with data from a related monitoring network of 24 wells and springs. All samples were analyzed for field measurements (water temperature, pH, specific conductance, and dissolved oxygen), major ions, trace elements, nutrients, volatile organic compounds, fecal indicator bacteria, and radon-222. Sub-sets of samples were analyzed for pesticides or semi-volatile organic compounds; site selection was based on local land use. Samples were grouped for comparison by geologic age of the aquifer, Groups included Cambrian, Ordovician, Silurian, Devonian, Pennsylvanian, Permian, and Quaternary aquifers. A comparison of samples indicated that geologic age of the aquifer was the largest contributor to variability in groundwater quality. This study did not attempt to characterize drinking water provided through public water systems. All samples were of raw, untreated groundwater. Drinking-water criteria apply to water that is served to the public, not to raw water. However, drinking water criteria, including U.S. Environmental Protection Agency (USEPA) maximum contaminant level (MCL), non-enforceable secondary maximum contaminant level (SMCL), non-enforceable proposed MCL, or non-enforceable advisory health-based screening level (HBSL), were used as benchmarks against which to compare analytical results. Constituent concentrations were less than the MCLs in most samples. However, some samples exceeded non-enforceable SMCLs, proposed MCLs, or advisory HBSLs. Radon-222 concentrations exceeded the proposed MCL of 300 pCi/L in 45 percent of samples, and iron concentrations exceeded the SMCL of 300 µg/L in 57 percent of samples. Manganese concentrations were greater than the SMCL (50 µg/L) in 62 percent of samples and greater than the HBSL (300 µg/L) in 25 percent of the samples. Other sampled constituents, including organic compounds and trace elements, exceeded drinking-water criteria at much lower frequencies. The radon-222 median concentrations in samples from Cambrian, Ordovician, Silurian, Permian, and Quaternary aquifers exceeded the proposed 300 pCi/L MCL. Although median radon concentrations for wells in Devonian, Mississippian, and Pennsylvanian aquifers were less than the proposed MCL, radon concentrations greater than the proposed MCL were measured in samples from aquifers of all geologic ages. The median iron concentrations for samples from Devonian and Pennsylvanian aquifers were greater than the 300 µg/L SMCL. Iron concentrations exceeded the SMCL in aquifers of all geologic ages, except Cambrian. Median concentrations of manganese exceeded the SMCL in samples from Devonian, Pennsylvanian, and Quaternary aquifers. As with iron, manganese concentrations were found to exceed the SMCL in at least one sample from aquifers of all geologic ages, except Cambrian. Pesticides were detected most frequently and in higher concentrations in limestone-dominated areas. Most of West Virginia’s agriculture is concentrated in those areas. This study, the most comprehensive assessment of West Virginia groundwater quality to date, indicates the water quality of West Virginia’s groundwater is generally good; in the majority of cases raw-water samples met primary drinking water-criteria. However, some constituents, notably iron and manganese, exceeded the secondary drinking criteria in more than half the samples.

West Virginia↗
USGS2018

Groundwater discharge characteristics for selected streams within the Loup River Basin, Nebraska, 2014–16

Streams in the Loup River Basin are sensitive to groundwater withdrawals because of the close hydrologic connection between groundwater and surface water. Groundwater discharge is the primary component of streamflow in the Loup River Basin and constitutes more than 90 percent of streamflow in the central part of the Sand Hills. To improve the understanding of geologic controls and various climatic and land-use changes on groundwater discharge, the U.S. Geological Survey (USGS), in cooperation with the Upper Loup Natural Resources District (NRD), the Lower Loup NRD, and the Nebraska Environmental Trust, studied the spatial and temporal characteristics of groundwater discharge within the Loup River Basin. This report documents the methods of data collection and analysis, which include the collection of approximately 350 river miles of aerial thermal infrared imagery and continuous groundwater-level and temperature data from six streamflow-gaging stations within the Loup River Basin. The results from the stream reconnaissance and examination of aerial thermal infrared imagery demonstrated the influence of the surficial and subsurface geology on the spatial characteristics of groundwater discharge to streams in the Loup River Basin. At the headwaters of the South Loup River, streamflow is sustained and increased from focused groundwater discharge emanating from Quaternary deposits at many small (less than 0.1 cubic foot per second) focused points. The volume of water produced from this dense network of focused groundwater discharge points along the North Fork South Loup River is sufficient to provide approximately 40 percent of the flow measured at the South Loup River at Arnold, Nebraska streamflow-gaging station (USGS station 06781600) during the irrigation season. Approximately 5 miles downstream from the South Loup River at Arnold, Nebr., streamflow-gaging station, the river incises into Pliocene-age sand and gravel deposits, which provide additional groundwater discharge to the stream. The streamflow of the South Loup River increases by a factor of 5 across a 62-mile reach of the middle South Loup River. Increases in streamflow along the upper Dismal River result from a dense network of focused groundwater discharge points within semiconsolidated Pliocene-age deposits. Below the Dismal River near Thedford, Nebr., streamflow-gaging station (USGS station 06775900), the Dismal River incises into the Ogallala Formation over a short reach before flowing over coarser, more permeable Quaternary-age alluvial deposits. Diffuse groundwater discharge sustains and increases the streamflow of the lower Dismal River in this reach. Groundwater sapping was evident on some stream reaches and has increased the size and flow of focused groundwater discharge points. Previous researchers have documented streambed incision and groundwater sapping on the upper Dismal River that have created and enlarged focused groundwater discharge points capturing additional groundwater. Similar processes appear to have played a role in the formation of larger focused groundwater discharge points, which sustain the flow of the middle South Loup River. The constant flow of groundwater into the South Loup River has removed finer-grained Quaternary sediments and further exposed Pliocene-age gravel deposits. Headward erosion is evident where some of the large focused groundwater discharge points have incised their own draws and terminate in bowl-like depressions away from the stream. Within the Loup River NRDs, the percentage of groundwater-irrigated land in a stream basin is one factor that affects groundwater discharge to streams. A striking example was at the South Loup River at Saint Michael, Nebr., groundwater and streamflow-gaging station (USGS station 06784000) where the shallow groundwater levels declined below the level of the stream during the middle to late part of the growing season (July to September) when consumptive groundwater use was at its peak. The South Loup River Basin above the South Loup River at Saint Michael, Nebr., streamflow-gaging station has the highest percentage of groundwater-irrigated row crops of all the basins examined in this study. Continuous groundwater and surface-water levels measured at the North Loup River at the Taylor, Nebr., streamflow-gaging station (USGS station 06786000) indicate that the stream is receiving groundwater throughout the year; however, when consumptive groundwater use peaks during the middle to late part of the growing season (July to September), the difference in elevation between the groundwater level and the stream elevation decreases, which indicates a reduction in the amount of groundwater discharge received.

Nebraska↗
USGS2019

Paleoliquefaction field reconnaissance in eastern North Carolina—Is there evidence for large magnitude earthquakes between the central Virginia seismic zone and Charleston seismic zone?

In June 2016, approximately 64 kilometers (km) of riverbank were examined along the Tar and Neuse Rivers near Tarboro and Kinston, North Carolina, for evidence of liquefaction-forming earthquakes. The study area is in the vicinity of the Grainger’s fault zone in eastern North Carolina. The Grainger’s fault zone is a fault zone in the inner Coastal Plain Province that has well-documented Paleogene and younger deformation of Cretaceous to Eocene strata. Low-magnitude earthquakes near the fault zone (for example, magnitude [M] 2.1 in 2013, 13 km south-southwest of Kinston) suggest larger earthquakes may have struck this region in the past. The study area is about equidistant from newly documented Holocene paleoliquefaction sites in the Central Virginia Seismic Zone (CVSZ) and liquefaction sites formed during the 1886 M7.1 Charleston, South Carolina earthquake. The northernmost Holocene paleoliquefaction features associated with the Charleston Seismic Zone (CSZ) are in Southport, North Carolina. Conditions suitable for liquefaction were identified at 38 sites on both rivers, but only one site was classified as highly susceptible. Stratigraphy consists of Paleozoic gneiss; Cretaceous sandstone/shale; Paleocene mudstone/claystone to Eocene fossiliferous limestone; Quaternary unconsolidated, crossbedded sand and gravel; and Holocene alluvium. Three sets of stratigraphic conditions suitable for liquefaction—unconsolidated source sand beneath capping strata—were identified in detailed examinations at 105 sites: (1) Holocene alluvial sand beneath alluvial silt and clay beds; (2) Quaternary terrace sand beneath beds of silt and clay; and (3) Holocene alluvial sand or Quaternary terrace sand capped by clay-rich Bt soil horizons. Weathered and unconsolidated Cretaceous sand capped by a Bt soil horizon was identified at one site, but the weathered sand is likely too compacted to liquefy readily. One outcrop containing three small sand dikes, and four outcrops of soft-sediment deformation features—mostly load casts—were observed, but none of these features could be conclusively established as seismogenic. A few examples of pseudo-sand-dikes were also identified: sand-filled cypress root casts and pedogenic weathering fronts created the appearance of sand dikes and sills. A comparable survey in 2015 of 119 km of riverbank exposures in the CVSZ yielded 19 paleoliquefaction sites of probable earthquake origin; these features formed from at least one M~6 earthquake in the past 6,000 years (6 ka). This survey in eastern North Carolina revealed no definitive paleoliquefaction features; earthquakes of sufficient magnitude to produce liquefaction likely have not affected this region during the Holocene.

North Carolina↗
USGS1976

Summary of geology and ground-water resources of Passaic County, New Jersey

Ground water in Passaic County occurs in intergranular openings of unconsolidated stratified deposits of Quaternary age and in joints and fractures in consolidated rocks of Precambrian, Paleozoic, and Triassic age. The Brunswick Formation of Triassic age is the most important aquifer in the southeastern one-third of Passaic County. Reported yields of public supply and industrial wells range from 50 to 510 gallons per minute (3 to 32 litres per second) and the median yield is 130 gallons per minute (8 litres per second). Most of these wells are 200 to 400 feet (61 to 122 metres) deep. The median yield of all public supply and industrial wells over 300 feet (91 metres) deep and 8 inches (203 millimetres) or larger in diameter is 230 gallons per minute (15 litres per second). Crystalline rocks of Precambrian age are the major source of ground water for domestic use in the northwestern two-thirds of Passaic County. Reported well yields range from 1 to 200 gallons per minute (.06 to 13 litres per second). The median reported yield of domestic wells is 5 gallons per minute (.31 litres per second) and that of public supply wells is 30 gallons per minute (2 litres per second). Other consolidated rocks--rocks of Paleozoic age and the Watchung Basalt of Traissic age--are utilized primarily for domestic water supplies in Passaic County. Reported yields of wells tapping the Paleozoic rocks range from less than 1 to 35 gallons per minute (.06 to 2 litres per second) and the median yield is 10 gallons per minute (.63 litres per second). Reported yields of domestic wells tapping the Watchung Basalt range from less than 1 to 40 gallons per minute (.06 to 3 litres per second) and the median yield is 12 gallons per minute (.76 litres per second). However, reported yields of nine industrial and commercial wells range from 50 to 180 gallons per minute (3 to 11 litres per second). Unconsolidated stratified deposits of Quaternary age are locally an important source of ground water for public supply and industrial use in parts of Passaic County. These deposits have not been extensively explored but are potentially an important source of ground water for future development. Reported yields of wells tapping the stratified deposits range from 4 to 920 gallons per minute (.25 to 58 litres per second). The median reported yield of domestic wells is 16 gallons per minute (1 litre per second) and that of public supply and industrial wells is 130 gallons per minute (8 litres per second. Depths of wells depend upon the thickness of the deposits. Reported depths range from 22 to 170 feet (7 to 52 metres). The quality of ground water in Passaic County varies from one aquifer to another. Water from the Precambrian rocks is soft to moderately hard (34 to 104 milligrams per litre) and is low in dissolved solids (66 to 159 milligrams per litre). Water from the Brunswick Formation is moderately hard to very hard (89 to 540 milligrams per litre). The dissolved solids content ranges from 129 to 563 milligrams per litre). The occurrence of more highly mineralized water at depth in the Brunswick Formation is indicated by an analysis, made in 1885, of 16,000 milligrams per litre of dissolved solids at a depth of 2,050 feet (625 metres) in a well in Paterson. Water from two wells tapping the Quaternary deposits is moderately hard (65 and 83 milligrams per litre) and has dissolved solids contents of 122 and 133 milligrams per litre). Water use from both surface and ground-water supplies in Passaic County averaged about 106 million gallons per day (4.6 cubic metres per second) in 1965. Ground water probably accounts for 5 to 10 percent of this total. Ground-water pumpage by the major public supply companies in the county has increased from 2.1 million gallons per day (.09 cubic metres per second) in 1951 to 4.39 million gallons per day (.19 cubic metres per second) in 1968. About 80 percent of the 4.39 million gallons per day (.19 cubic metres per second) was from wells tapping the Brunswick Formation in the southern part of the county.

New Jersey↗
USGS1985

Results of geohydrologic test drilling in the eastern Snake River Plain, Gooding County, Idaho

A 1,123-foot test hole was core drilled near Wendell, Idaho, during 1981-82 as part of the Snake River Plain regional aquifer study. An upper basalt unit, an intermediate unconsolidated sedimentary rock unit, and a lower basalt unit were penetrated by the test hole. Drilling verified that the upper several hundred feet of high-resistivity material, as determined by surface electrical soundings, is basalt. Core examination, laboratory analysis, and correlation with other drill holes indicated that the basalt is typical of Quaternary basalt of the Snake River Group. Quaternary basalt in the test hole is 200 feet thick. Correlation with other drill holes and comparison with rock outcrops near the Snake River and in the Snake River canyon suggest that the underlying sediments and lower basalt unit are parts of the Tertiary and Quaternary Glenns Ferry Formation and Tertiary Banbury Basalt. Piezometers in the hole verify upward movement of water in a major discharge area for the regional aquifer. Hydraulic head in the bottom of the hole is about 155 feet higher than the water table. Lithologic sequence in the test hole correlates well with sequences in deep drill holes at scattered locations on the plain. (USGS)

Idaho↗
USGS1995

Reconnaissance of ground-water quality in the North Platte Natural Resources District, western Nebraska, June-July 1991

One-hundred twenty wells completed in unconfined Quaternary alluvial, Ogallala, Arikaree, Brule fractured, sand and confined Chadron and undifferentiated Cretaceous water-bearing units were sampled in June and July 1991 to characterize the quality of ground water in the study area. More than 75 percent of the water samples had nitrate and nitrite as nitrogen concentrations equal to or less than 6.0 milligrams per liter. Samples from six wells completed in Quaternary alluvial and Brule fractured water-bearing units exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level of 10 milligrams per liter nitrate and nitrite as nitrogen. Water from several wells completed in Quaternary alluvial and the Brule water-bearing units had detectable concentrations of alachlor, atrazine, deethylatrazine, or prometon. Major element concentrations in water from 44 wells indicated that the water-bearing units had distinct chemistry. Water from unconfined water- bearing units generally was a calcium bicarbonate type and water from the confined water-bearing units generally was a sodium bicarbonate type. Measurements of pH and concentrations of dissolved solids, sulfate, chloride, fluoride, arsenic, beryllium, manganese, adjusted gross alpha activities, radon, and uranium in ground water exceeded final or proposed U.S. Environmental Protection Agency Maximum Contaminant Levels or Secondary Maximum Contaminant Levels.

Water-Resources Investigations Report↗
USGS1995

Hydrogeology of Cibola County, New Mexico

The hydrogeology of Cibola County, New Mexico, was evaluated to determine the occurrence, availability, and quality of ground-water resources. Rocks of Precambrian through Quaternary age are present in Cibola County. Most rocks are sedimentary in origin except for Precambrian igneous and metamorphic rocks exposed in the Zuni Uplift and Tertiary and Quaternary basalts in northern and central parts of the county. The most productive aquifers in the county include (youngest to oldest) Quaternary deposits, sandstones in the Mesaverde Group, the Dakota-Zuni-Bluff aquifer, the Westwater Canyon aquifer, the Todilto- Entrada aquifer, sandstone beds in the Chinle Formation, and the San Andres-Glorieta aquifer. Unconsolidated sand, silt, and gravel form a mantle ranging from a few inches to 150 to 200 feet over much of the bedrock in Cibola County. Well yields range from 5 to 1,110 gallons per minute. Dissolved-solids concentrations of ground water range from 200 to more than 5,200 milligrams per liter. Calcium, magnesium, bicarbonate, and sulfate are the predominant ions in ground water in alluvial material. The Mesaverde Group mainly occurs in three areas of the county. Well yields range from less than 1 to 12 gallons per minute. The predominant ions in water from wells in the Mesaverde Group are calcium, sodium, and bicarbonate. The transition from calcium-predominant to sodium-predominant water in the southwestern part of the county likely is a result of ion exchange. Wells completed in the Dakota-Zuni-Bluff aquifer yield from 1 to 30 gallons per minute. Dissolved-solids concentrations range from 220 to 2,000 milligrams per liter in water from 34 wells in the western part of the county. Predominant ions in the ground water include calcium, sodium, sulfate, and bicarbonate. Calcium predominates in areas where the aquifer is exposed at the surface or is overlain with alluvium. Sandstones in the Chinle Formation yield from 10 to 300 gallons per minute to wells in the Grants-Bluewater area. In the western part of the county, sodium and bicarbonate predominate in water from the Chinle Formation. In the eastern part of the county, water quality is more variable than elsewhere and the predominant constituents include calcium, sodium, sulfate, and chloride. Well yields from the San Andres-Glorieta aquifer in the Grants- Bluewater area are as much as 2,830 gallons per minute, whereas the maximum recorded pumping rate from the aquifer in other areas of the county is 88 gallons per minute. Dissolved-solids concentrations of ground-water range from about 130 to 4,200 milligrams per liter, and the water generally is a calcium bicarbonate sulfate type.

Water-Resources Investigations Report↗
USGS2000

Analysis of nutrients, selected inorganic constituents, and trace elements in water from Illinois community-supply wells, 1984–91

The lower Illinois River Basin (LIRB) study unit is part of the National Water-Quality Assessment program that includes studies of most major aquifer systems in the United States. Retrospective water-quality data from community-supply wells in the LIRB and in the rest of Illinois are grouped by aquifer and depth interval. Concentrations of selected chemical constituents in water samples from community-supply wells within the LIRB vary with aquifer and depth of well. Ranked data for 16 selected trace elements and nutrients are compared by aquifer, depth interval, and between the LIRB and the rest of Illinois using nonparametric statistical analyses. For all wells, median concentrations of nitrate and nitrite (as Nitrogen) are highest in water samples from the Quaternary aquifer at well depths less than 100 ft; ammonia concentrations (as Nitrogen), however, are highest in samples from well depths greater than 200 ft. Chloride and sulfate concentrations are higher in samples from the older bedrock aquifers. Arsenic, lead, sulfate, and zinc concentrations are appreciably different between samples from the LIRB and samples from the rest of Illinois for ground water from the Quaternary aquifer. Arsenic concentration is highest in the deep Quaternary aquifer. Chromium, cyanide, lead, and mercury are not frequently detected in water samples from community-supply wells in Illinois.

Illinois↗
USGS1960

Geology and ground water in the Platte-Republican Rivers watershed and the Little Blue River basin above Angus, Nebraska, with a section on chemical quality of the ground water

This report describes an area of about 7,300 square miles in south-central Nebraska. Approximately one-fourth of the area, largely at its east end, consists of an undissected southeastward-sloping upland plain and is almost wholly irrigable; the remainder is in various stages of dissection and only parts of it are suitable for irrigation. Although some of the deeper lying bedrock formations are potential sources of water supply, they are not likely to be tapped in the near future because abundant supplies are available at shallower depth from semiconsolidated and unconsolidated deposits. The Ogallala formation of Tertiary (Pliocene) age consists of gravel, sand, silt, and volcanic ash, some layers of which are partly cemented. It was deposited by eastward-flowing streams, which formed a constructional plain above a surface into which the streams had previously eroded broad valleys. In turn, valleys were cut into the surface of the Ogallala before the overlying deposits of gravel, sand, silt, and clay of Quaternary (Pleistocene) age were laid down, also forming a constructional plain. During Recent time, streams have dissected the older deposits and have deposited thin alluvium in their valleys; also, several parts of the area have become mantled by wind-deposited sand. Because during Tertiary and Quaternary time the area repeatedly was the site of deposition and erosion, the thickness of all the stratigraphic units differs markedly from place to place. In general, however, the Ogallala formation thins eastward and in the central and eastern parts of the area is overlain by the eastward-thickening deposits of Pleistocene age. The maximum thickness of the Ogallala formation is about 500 feet, and the maximum thickness of the Pleistocene deposits is a little more than 300 feet. Each thins to a featheredge and is completely absent in parts of the area. The water-bearing part of the combined Tertiary and Pleistocene deposits is considered to be a single zone of saturation because the ground water, as it percolates southeastward beneath the area, moves out of the Tertiary and into the Quaternary deposits without apparent hindrance. The water that enters the area as underflow from the west is augmented within the area by water that infiltrates from the land surface. The principal sources of irrigating water are precipitation, seepage from canals and reservoirs, and applied irrigation water. Except for the water withdrawn through wells or discharged by natural processes where valleys have been cut into the zone of saturation, ground water leaves the area as underflow into the Platte River valley on the north, the Blue River drainage basin on the east, or the Republican River valley on the south. Part of the water used for irrigation and watering livestock and all the water used in rural and urban homes, in public buildings, and for industrial purposes is obtained from wells, To date (1952) there is no indication that the supply of ground water is being depleted faster than it is being replenished; instead, studies indicate that greater quantities can be withdrawn without causing an excessive decline of the water table. An increase of ground-water withdrawals to a sustainable maximum, however, will be possible only if the points of withdrawal are scattered fairly uniformly. It is estimated that annual withdrawals per township should not exceed 2,100 acre-feet where infiltrating precipitation is the only source of recharge, or 3,000 acre-feet where other sources of recharge are significant. Although perennial withdrawals of this amount could be sustained indefinitely, they would cause some lowering of the water table and eventually a decrease in the amount of water discharged from the area by natural means. The ground water is of the calcium bicarbonate type. In much of the area it is hard or very hard, and in places it contains excessive amounts of iron. In all other respects the water is chemically suitable for domesti

Nebraska↗
USGS1963

Geology and ground-water resources of Hays County, Texas

The Edwards limestone of Early Cretaceous age is the chief aquifer for San Marcos Springs and about 160 other springs and wells in Hays County, along the Balcones fault zone in South-central Texas. Hays County is underlain by a basement of Paleozoic rocks; and in the southeastern part of the county the Hosston and Sligo formations of Early Cretaceous age, correlative with the Coahuila series of Mexico, have been encountered in the subsurface. Rocks exposed in the county are principally Cretaceous and Quaternary sedimentary units, which are assigned to the Trinity, Fredericksburg, and Washita groups in the Comanche series; the Eagle Ford shale, Austin chalk, Taylor marl, and Navarro group in the Gulf series: and the Leona formation and equivalent rocks in the Pleistocene series. Recent alluvium and colluvium locally overlie the older rocks. In addition to the Edwards limestone in the Fredericksburg group, waterbearing rock units in Hays County include the Pearsall formation (Travis Peak of outcrop areas) and the Glen Rose limestone in the Trinity group, the Austin chalk and Taylor marl, and the Quaternary rocks. The surface slope and regional dip are toward the southeast. Several normal strike faults have displaced the Cretaceous rocks downward to the southeast, the aggregate displacement being about 1,700 feet within the county. The boundaries of the Edwards limestone ground-water reservoir are formed by major faults which are the major controls of movement of water. Much of the water discharged at San Marcos Springs is derived from influent seepage from streams and infiltration from precipitation in recharge areas southwest of Hays County. The average underground inflow from Comal County through the Edwards limestone reservoir is estimated as 70,000 acre-feet per year for the period 1934-47. The discharge of San Marcos Springs, averaging about 55 million gallons a day during 1955, greatly exceeds local ground-water recharge within Hays County. Depth to water, direction of movement of water, subsurface location of aquifers, and quality of water in Hays County have been determined from records of 519 wells and springs, drillers' logs of 49 wells, periodic water-level measurements in about 70 wells, and chemical analyses of water samples from 238 wells and springs. Ground water from wells in the Pearsall formation generally contains less than 500 parts per million of dissolved solids. Water from the Glen Rose limestone in some places contains more than 500 parts per million of sulfate and more than 1,000 parts per million of dissolved solids; locally it is high in nitrate also. Except in the southeastern part of the county, water from the Edwards limestone is commonly very hard but is otherwise of good quality for most uses. Analyses of two water samples from the Austin chalk indicate a high content of bicarbonate. Water from the Taylor marl and from Quaternary sediments generally is hard, and locally it contains excessive nitrate. Most wells in Hays County are used for domestic and stock supplies. About 20 wells, most of them in the Edwards limestone, yield water in relatively large amounts for industrial use, irrigation, or public supplies.

Water Supply Paper↗
USGS1963

Water resources of Red River Parish, Louisiana

Red River Parish is on the eastern flank of the Sabine uplift in northwestern Louisiana. The 'area is underlain by lignitic clay and sand of Paleocene and Eocene age which dip to the east at the rate of about 30 feet per mile. The Red River is entrenched in these rocks in the western part of the parish. Alternating valley filling and erosion during the Quaternary period have resulted in the present lowland with flanking terraces. In the flood-plain area moderate to large quantities of very hard, iron-bearing water, suitable for irrigation, are available to wells in the alluvial sand and gravel of Quaternary age. The aquifer ranges in thickness from 20 to slightly more than 100 feet. It is recharged by downward seepage of rainfall through overlying clay and silt, by inflow from older sands adjacent to and beneath the entrenched valley, and by infiltration from the streams where the water table is below stream level during flood stages or as a result of pumping. Water levels are highest in the middle of the valley. Ground water moves mainly toward the Red River on the east and Bayou Pierre on the west, but small amounts move down the valley. Computations based on water-level and aquifer-test data indicate that the Quaternary alluvium contains more than 330 billion gallons of ground water in storage and that the maximum discharge of ground water to the streams is slightly more than 30 mgd (million gallons per day). At times of high river stage, surface water flows into the aquifer at a rate that depends in part upon the height and duration of the river stage. Moderate supplies of soft, iron-bearing water may be obtained from dissected Pleistocene terrace deposits that flank the flood plains of the Red River and Black Lake Bayou. However, the quantity of water that can be pumped from these deposits varies widely from place to place because of differences in the areal extent and saturated thickness of the segments of the deposits; this extent and thickness are governed in turn by the amount of erosion the deposits have undergone. Beds of fine-grained lignitic sands of Tertiary age contain water of generally good quality to depths of 150 to 450 feet. The thinness and low permeability of the sands restrict their development to low-yield wells. Water from these sands in the western part of the parish, where they lie beneath the alluvial valley, is more mineralized than that from the younger Tertiary sands exposed in the east-central area. Streamflow records have been collected on the principal streams in Red River Parish since 1939. Additional spot low-flow data were obtained on several small streams originating within the parish for a study made in connection with the preparation of this report. Quality-of-water data for streams in the parish were collected on an occasional spot-sampling basis prior to and during this investigation. The largest source of surface water in the parish is the Red River, which drains approximately 63,400 square miles upstream from the parish. The Red River has an average flow of about 13,100 cfs (cubic feet per second), or about 8,500 mgd. Many of the streams that drain the upland area are not dependable sources of supply because their flows are not well sustained during dry seasons. The average annual precipitation over the parish is about 52 inches, of which about 17 inches becomes runoff; this runoff is equivalent to a continuous flow of about 1.25 cfs per square mile. Seasonal and annual runoff varies, but no significant trends have been noticed. The principal surface-water problems in the parish pertain to flood control, drainage, irrigation, and navigation. Flood problems have been alleviated considerably by the operation of Denison Dam (Lake Texoma), the completion of levees on the Red River, channel improvements on Bayou Pierre, and the completion of Wallace Lake reservoir on Cypress Bayou. There are wet lands along the Red River that would be very productive if properly drained

Water Supply Paper↗