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At least 343 records · Page 19Linked to original sources
USGS2024

Inset groundwater-flow models for the Cache and Grand Prairie Critical Groundwater Areas, northeastern Arkansas

The water resources in the Mississippi alluvial plain, located in parts of Missouri, Kentucky, Tennessee, Mississippi, Louisiana, and Arkansas, supports a multibillion-dollar agricultural industry that relies heavily on pumping of groundwater for irrigation of crops and aquaculture. The primary source of groundwater for agricultural-related pumping is the Mississippi River Valley alluvial aquifer, which has declined in storage for decades; secondary groundwater sources include the middle Claiborne aquifer and Wilcox aquifer system. Two areas in northeastern Arkansas that lie within the Mississippi alluvial plain, part of the Cache and Grand Prairie regions, have been designated as Critical Groundwater Areas owing to decades of groundwater declines that resulted from past and current water use. The multidisciplinary Mississippi Alluvial Plain project, led by the U.S. Geological Survey, and funded by their Water Availability and Use Science Program, included objectives to develop numerical groundwater models in focus regions, including the part of the Cache and Grand Prairie regions of northeastern Arkansas. Two inset models were developed using the child model capabilities of MODFLOW 6, the U.S. Geological Survey’s Modular Hydrologic Model simulation software. Both models, called the Cache model and Grand Prairie model, simulated the groundwater system and surface-water/groundwater interactions for the Mississippi River Valley alluvial aquifer and underlying Tertiary-age aquifers and confining units to the Midway confining unit. Each model was spatially discretized into 500-meter x 500-meter orthogonal cells on a grid with 5-meter constant-thickness vertical layers that represented the Mississippi River Valley alluvial aquifer and increasing thickness layers for the aquifers and confining units below the alluvial aquifer. The Cache and Grand Prairie models were calibrated with the PEST++ iterative ensemble smoother Version 5 and employed high dimensional parameterization schemes of 13,740 and 30,436 parameters, respectively. The Cache mean absolute residual for groundwater-level observations within each model domain for the priority well was 1.58 meters. Grand Prairie mean absolute residuals for the alluvial aquifer and middle Claiborne aquifer groundwater-level observations were 2.71 and 10.78 meters, respectively. The groundwater budgets for the Cache and Grand Prairie models were characterized by substantial outflows to irrigation wells, which constituted about 52 and 54 percent of all outflows, with the primary source of water to those wells being releases from unconfined aquifer storage.

Arkansas↗
USGS2016

Geologic and geophysical models for Osage County, Oklahoma, with implications for groundwater resources

This report summarizes a three-dimensional (3-D) geologic model that was constructed to provide a framework to investigate groundwater resources of the Osage Nation in northeastern Oklahoma. This report also presents an analysis of an airborne electromagnetic (AEM) survey that assessed the spatial variation of electrical resistivity to depths as great as 300 meters in the subsurface. The report and model provide support for a countywide assessment of groundwater resources, emphasizing the Upper Pennsylvanian rock units in the shallow subsurface of central and eastern Osage County having electrical resistivity properties that may indicate aquifers. Surface outcrops and subsurface stratigraphic picks on wire-line geophysical logs of Upper Pennsylvanian–Lower Permian sedimentary rock were used to construct a 3-D model of the geologic subsurface as an aid for evaluating groundwater resources in Osage County. Quaternary alluvium and terraces along major streams and the Arkansas River are included in the geologic framework model. Data from the AEM survey were subjected to quality-control procedures, truncated at depth of investigation (DOI), and then used to build a 3-D electrical resistivity model making use of secondary and tertiary interpolation profiles between primary data profiles. The AEM data highlight westward-inclined resistivity gradients that parallel the shallow dip of bedrock strata; bodies have resistivity >30 ohm-meters, and extend as much as 10 kilometers (km) down the dip of host geologic units. Volume analysis and internal imaging of an integrated 3-D geology and electrical resistivity model give a proxy for likely aquifer units with large relative volumes of high resistivity: Quaternary alluvium, Elgin Sandstone Lentil in the upper part of the Vamoosa Group, Tallant Formation, and parts of a combined Wann-Iola-Chanute Formation. Less voluminous, high-resistivity bodies correspond to intervals in the lower part of the Vamoosa Group in the east-central part of the county and probable limestone intervals in the upper part of the Vanoss Group in the northwest part of the county. Northwestern and eastern troughs of potable water previously defined for central Osage County generally correspond to down-dip projections of high-resistivity bodies associated with the Elgin Sandstone Lentil of the Vamoosa Group and Tallant Formation, respectively.

Oklahoma↗
USGS1969

Structural geology of the Quad-Wyoming-Line Creeks area, Beartooth Mountains, Montana

The Quad-Wyoming-Line Creeks area is in the northeastern part of the Beartooth Mountains of Montana. The rocks of the area consist mainly of banded migmatite, granitic gneisses, amphibolite, quartzite, and agmatite; small amounts of biotite schist and biotite gneiss, iron-silicate rocks, ultramafic rocks, mafic dikes, and felsic porphyries are also present. Quartzite outcrops continuously around the major folds, and agmatite is especially widespread in the axial zone of a major anti-form. Two fold sets have been revealed by detailed mapping (scale 1:7200) and statistical analysis of the penetrative subfabric elements. The large later folds, F 2 , are the south-plunging Quad Creek synform and the south-southwest-plunging Wyoming Creek antiform; they are nearly upright and non-isoclinal. A metanorite intrusion is located in the axial zone of the Quad Creek synform. Small F 2 fold style varies from similar in relatively ductile rocks to open, concentric folds in non-ductile rocks. Only one large F 1 , located immediately north of the metanorite pluton, has been mapped. F 1 folds are characteristically similar in style. Refolding of small F 1 folds by small F 2 folds has been observed throughout the map area. Statistical analysis of the compositional layering, So, and the axial planes of small F 1 folds, S 1 , shows that the πS 0 - and πS 1 -axes constructed in the Wyoming Creek antiform are nearly coincident with each other and with south-southwest-plunging maxima of small F 2 fold axes, B 2 . Both B 2 and the axial planes of F 2 folds, S 2 , are dispersed, showing that the later folds are noncylindrical and nonplane. The axes of small F 1 folds, B 1 , are generally dispersed along well defined π-girdles. B 1 and B 2 maxima are generally coincident at some stations in the Wyoming Creek antiform-axial zone, suggesting that B 1 and B 2 are, at least locally, collinear. The long axes of hornblende crystals, L 1 , are also dispersed, but are not parallel to B 1 ; the L 1 -subfabric appears to indicate that L 1 developed during the F 1 folding but plunged somewhat more steeply to the south-southwest to south than Bi and that the F 2 folds are concentric rather than similar in the amphibolite. In the Quad Creek synform (F 2 ), all of the above-mentioned fabric elements diverge around the north side of the metanorite body. The Precambrian deformational history of the present map area, and probably the remainder of the eastern Beartooth Mountains, appears to be comprised of two phases of folding. During the first phase (F 1 ) south-southwest plunging, isoclinal or nearly isoclinal folds formed by passive flow during metamorphism to at least the upper amphibolite facies; these F, folds were not upright and may have been nearly recumbent. L 1 was formed during this phase. Metamorphic differentiation of a sedimentary sequence occurred at this time, but it is not clear whether any new material was added. The second phase of deformation is characterized by upright, non-isoclinal folds which also formed about south-southwest to south plunging axes. Flexural flow was the dominant mechanism in the development of the Quad Creek synform and the Wyoming Creek antiform, but passive flow was important in layers of ductile rocks. Granitization was generally synchronous with the F 2 phase; pegmatite dikes were emplaced later in a passive manner. Quartzite and amphibolite acted as resisters to granitization; their termination in granitic gneisses and migmatites is usually most adequately explained by refolding rather than granitization of the quartzite. It is possible that partial melting occurred in some areas such as the agmatized zones. Time of emplacement of the metanorite body is still questionable, but it clearly predates the F 2 folding; intrusion prior to F 1 is probable because B 1 , B 2 , and L 1 diverge in the vicinity of the body.

Montana↗
USGS1985

Reconnaissance geology of the Al Ba'ayith quadrangle, sheet 26/41 D, Kingdom of Saudi Arabia

The Al Ba'ayith quadrangle, located in the northeastern part of the Arabian Shield, is underlain by upper Proterozoic intrusive rocks and volcanogenic layered sequences bounded by unconformities. The oldest rocks are silicic volcanic rocks of the Banana formation that is tentatively assigned to the Hulayfah group. Successively younger layered rocks are the Maraghan formation of the Murdama group, consisting of lithic graywacke, siltstone, and shale; the Hibshi formation, coarse-grained lithic sandstone and conglomerate; the Sufran formation, dacitic and andesitic lava flows and ash-flow tuffs; the Jurdhawiyah formation, andesitic flows and agglomerate, and conglomeratic sandstone; and the Hadn formation, rhyolite flows and ash-flow tuffs, conglomerate, sandstone, and andesite flows. Plutonic rocks are of four main age groups: an early group consisting of orthogneiss of granodioritic and granitic composition, and metagabbro; a pre-Hibshi group consisting of the Murran complex (diorite and quartz diorite) and quartz monzodiorite; a post-Hibshi group, consisting of altered mafic plutonic rocks, granodiorite of the Idah suite, and monzogranite of the Shuwayman suite; and a latest Precambrian group of highly evolved granitic rocks, consisting of alkali-feldspar granite, granophyre, and syenogranite. Structures in the orthogneiss and metagabbro trend northeast to northwest, and in the Murran complex, generally east. The Maraghan formation was folded and thrust over the Hibshi formation along the northeast-trending Raha fault. The Jurdhawiyah formation is at the northern margin of the east-trending Shuqrah basin. Northwest-trending left-lateral faults probably belong to the Najd fault system. Quaternary surficial deposits mantle large areas of the quadrangle, and consist of sheet gravel, alluvial fan gravel, eolian and alluvial sand and silt, and sabkhah deposits. Gold-bearing quartz veins occur associated with small plutons of the Idah suite in the southeastern part of the quadrangle, and have been mined in the past. Ironstones, near Murran in the center of the quadrangle contain trace amounts of silver and gold.

Open-File Report↗
USGS1952

Reconnaissance for uraniferous rocks in northwestern Colorado, southwestern Wyoming, and northeastern Utah

Previous discoveries and studies of radioactive lignites of Tertiary age in North Dakota, South Dakota, Montana, and Wyoming led the Geological Survey in 1950 to do reconnaissance in the Green River and Uinta Basin of Wyoming and Utah, where similar lignites were believed to be present. Because of the common association of uranium with copper deposits and the presence of such deposits in the Uinta Basin, several areas containing copper-uranium minerals were also examined. No deposits commercially exploitable under present conditions were found. Samples of coal from the Bear River formation at Sage, Wyo., assayed 0.004 to 0.013 percent uranium in the ash; in the old Uteland copper mine in Uinta County, Utah, 0.007 to 0.017 percent uranium; in a freshwater limestone, Duchesne County, Utah, as much as 0.019 percent uranium; and in the Mesaverde formation at the Snow and Bonniebell claims near Jensen, Uintah County, Utah, 0.003 to 0.090 percent uranium. Maps were made and samples were taken at the Skull Creek carnotite deposits in Moffat County, Colo. (0.006 to 0.16 percent uranium); at the Fair-U claims in Routt County, Colo. (0.002 to 0.040 percent uranium); and at the Lucky Strike claims near Kremmling in Grand County, Colo. (0.006 to 0.018 percent uranium).

Colorado;Utah;Wyoming↗
USGS2014

Structural controls on geothermal circulation in Surprise Valley, California: A re-evaluation of the Lake City fault zone

Faults and fractures play an important role in the circulation of geothermal fluids in the crust, and the nature of that role varies according to structural setting and state of stress. As a result, detailed geologic and geophysical mapping that relates thermal springs to known structural features is essential to modeling geothermal systems. Published maps of Surprise Valley in northeastern California suggest that the “Lake City fault” or “Lake City fault zone” is a significant structural feature, cutting obliquely across the basin and connecting thermal springs across the valley. Newly acquired geophysical data (audio-magnetotelluric, gravity, and magnetic), combined with existing geochemical and geological data, suggest otherwise. We examine potential field profiles and resistivity models that cross the mapped Lake City fault zone. While there are numerous geophysical anomalies that suggest subsurface structures, they mostly do not coincide with the mapped traces of the Lake City fault zone, nor do they show a consistent signature in gravity, magnetics, or resistivities that would suggest a through-going fault that would promote connectivity through lateral fluid flow. Instead of a single, continuous fault, we propose the presence of a deformation zone associated with the growth of the range-front Surprise Valley fault. The implication for geothermal circulation is that this is a zone of enhanced porosity but lacks length-wise connectivity that could conduct fluids across the valley. Thermal fluid circulation is most likely controlled primarily by interactions between N-S–trending normal faults.

California↗
USGS2004

Two-dimensional hydrodynamic simulation of surface-water flow and transport to Florida Bay through the Southern Inland and Coastal Systems (SICS)

Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly in the SWIFT2D model, and that the spatial and temporal resolution of these processes in the model is adequate. Sensitivity analyses were conducted to determine the effect of changes in boundary conditions and parameter values on simulation results, which aided in identifying areas of greatest uncertainty in the model. The parameter having the most uncertainty (most in need of further field study) was the flow coefficient for coastal creeks. Smaller uncertainties existed for wetlands frictional resistance and wind. Evapotranspiration and boundary inflows indicated the least uncertainty as determined by varying parameters used in their formulation and definition. Model results indicated that wind was important in reversing coastal creek flows. At Trout Creek (the major tributary connecting Taylor Slough wetlands with Florida Bay), flow in the landward direction was not simulated properly unless wind forcing was included in the simulation. Simulations also provided insight into the major influence that wind has on salinity mixing along the coast, the varying distribution of wetland flows at differing water levels, and the importance of topography in controlling flows to the coast. Slight topographic variations were shown to highly influence the routing of water. A multiple regression analysis was performed to relate inflows at the northern boundary of Taylor Slough bridge to a major pump station (S-332) north of the SICS model area. This analysis allows Taylor Slough bridge boundary conditions to be defined for the model from operating scenarios at S-332, which should facilitate use of the SICS model as an operational tool.

Florida↗
USGS1999

Soil-calcium depletion linked to acid rain and forest growth in the eastern United States

Since the discovery of acid rain in the 1970's, scientists have been concerned that deposition of acids could cause depletion of calcium in forest soils. Research in the 1980's showed that the amount of calcium in forest soils is controlled by several factors that are difficult to measure. Further research in the 1990's, including several studies by the U.S. Geological Survey, has shown that (1) calcium in forest soils has decreased at locations in the northeastern and southeastern U.S., and (2) acid rain and forest growth (uptake of calcium from the soil by roots) are both factors contributing to calcium depletion.

Water-Resources Investigations Report↗
USGS1979

Coal geology of the Northeast Circle area, McCone and Dawson counties, Montana

The Northeast Circle area is in central McCone and northern Dawson Counties, northeastern Montana. The area encompasses about 940 square miles and has a maximum relief of greater than 1,000 feet. The lowest point (altitude of less than 2,200 feet) is in the Redwater River Valley in the northern part of the area. The highest point (altitude of less than 3,200 feet) is on the Yellowstone-Missouri divide, located in parts of Tps. 18 and 19 N., Rso 49, 50, and 51E., and T. 20 N., Rs. 52 and 53 E. Surface exposures in most of the area consist of yellowish or light-colored sandy shales of the Tongue River Member of the Paleocene Fort Union Formation. The coal beds in the Northeast Circle area occur in the lower 500 feet of this member and are persistent in the field. The predominant structural features of the area are the northeast end of the Weldon monocline-fault in Tps. 21 and 22 N., R. 47 E., and a small steep depression near Circle in sec. 10, T. 19 N., R. 48 E. Otherwise, the structure of the area is nearly flat. Coal in the Northeast Circle area is composed of six main beds: the S, L1, R, Q, P, and Pust beds, in ascending stratigraphic order. Of these, the S, Pust, and P beds are the thickest. The S bed is more than 20 feet thick in some places, but usually ranges in thickness from 6 to 10 feet. The Pust bed, which is about 430-490 feet above the S bed, is more than 18 feet thick in the upper bench and as much as 9 feet thick in the lower bench. Coal thickness in the P bed varies from 0 to 10.5 feet. The other coal seams in the area are generally less than 5 feet thick. All coals are lignite in rank.

Open-File Report↗
USGS1905

The Fairhaven gold placers, Seward Peninsula, Alaska

This manuscript is based on a geologic and topographic reconnaissance survey, made during the summer of 1903, of an important placer-gold district in the northeastern part of Seward Peninsula. The report is accompanied by a reconnaissance map by Mr. D. C. Witherspoon, topographer, under whose directions the field operations were carried out. Surveys were begun in Seward Peninsula in 1899, soon after the discovery of the rich placers of Nome, and, in view of the great economic importance of the field, have been extended as rapidly as the appropriations permitted. It was early recognized that here, as elsewhere in Alaska, it would be better to obtain general topographic and geologic results, to be immediately available to the mining public, than to attempt exhaustive surveys and studies of small areas. This has been the guiding policy in formulating and executing the plans. As a result, there have been issued a number of publications (including reconnaissance maps) which, though only of a preliminary character, have been, because of their timeliness, of much value to the mining public. With the appearance of the following report this first epoch in the surveys will have closed, for there will be available complete reconnaissance reports and maps of the entire Seward Peninsula. These general reports and maps should be followed by more detailed surveys; these have been begun, and it is purposed to carry them forward as rapidly as circumstances will permit. In taking up areas for detailed investigations the attempt will be made to study first those of greatest economic interest.

Alaska↗
USGS2005

Petroleum systems and geologic assessment of oil and gas in the Southwestern Wyoming Province: Wyoming, Colorado and Utah

The U.S. Geological Survey (USGS) completed an assessment of the undiscovered oil and gas potential of the Southwestern Wyoming Province of southwestern Wyoming, northwestern Colorado, and northeastern Utah (fig. 1). The USGS Southwestern Wyoming Province for this assessment included the Green River Basin, Moxa arch, Hoback Basin, Sandy Bend arch, Rock Springs uplift, Great Divide Basin, Wamsutter arch, Washakie Basin, Cherokee ridge, and the Sand Wash Basin. The assessment of the Southwestern Wyoming Province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation, and migration), reservoir rocks (sequence stratigraphy, petrophysical properties), and hydrocarbon traps (trap types, formation, and timing). Using this geologic framework, the USGS defined 9 total petroleum systems (TPS) and 23 assessment units (AU) within these TPSs, and quantitatively estimated the undiscovered oil and gas resources within 21 of the 23 AUs.

Colorado, Utah, Wyoming↗
USGS2007

Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers of Southern and Northeastern Arkansas, 2006

The Cockfield Formation of Claiborne Group and the Wilcox Group contain aquifers that provide sources of ground water in southern and northeastern Arkansas. In 2000, about 9.9 million gallons per day was withdrawn from the Cockfield Formation of Claiborne Group and about 22.2 million gallons per day was withdrawn from the Wilcox Group. Major withdrawals from the aquifers were for industrial and public water supplies. A study was conducted by the U.S. Geological Survey in cooperation with the Arkansas Natural Resources Commission and the Arkansas Geological Survey to determine the water level associated with the aquifers in the Cockfield Formation of Claiborne Group and the Wilcox Group in southern and northeastern Arkansas. During February and March 2006, 56 water-level measurements were made in wells completed in the Cockfield aquifer and 59 water-level measurements were made in wells completed in the Wilcox aquifer, 16 in southwestern and 43 in northeastern Arkansas. This report presents the results as potentiometric-surface maps and as long-term water-level hydrographs. The regional direction of ground-water flow in the Cockfield Formation of Claiborne Group generally is towards the east and southeast, away from the outcrop, except in areas of intense ground-water withdrawals, such as western Drew County, southeastern Lincoln County, southwestern Calhoun County, and near Crossett in Ashley County. There are three cones of depression indicated by relatively low water-level altitudes in southeastern Lincoln County, southwestern Calhoun County, and near Crossett in Ashley County. The lowest water-level altitude measured was 44 feet above the National Geodetic Vertical Datum of 1929 in Lincoln County; the highest water-level altitude measured was 346 feet above the National Geodetic Vertical Datum of 1929 in Columbia County at the outcrop area. Hydrographs from 40 wells with historical water levels from 1986 to 2006 were evaluated using linear regression to calculate the annual rise or decline. Calhoun and Cleveland Counties have mean annual rises from 0.01 to 0.07 feet per year. Arkansas, Ashley, Bradley, Chicot, Columbia, Drew, Lincoln, and Union Counties have mean annual declines from 0.4 to 0.55 feet per year. Desha County has a mean annual decline of about 1.35 feet per year. The direction of ground-water flow in the southwestern study area of the Wilcox Group generally is south and east. The lowest water-level altitude measured in southwestern Arkansas was 147 feet above the National Geodetic Vertical Datum of 1929 near the Ouachita River in Clark County; the highest water-level altitude measured was 397 feet above the National Geodetic Vertical Datum of 1929 in the outcrop area of Hempstead County. The direction of ground-water flow in the northeastern study area of the Wilcox Group generally is south and east. The lowest water-level altitude measured in northeastern Arkansas was 120 feet above the National Geodetic Vertical Datum of 1929 near West Memphis in Crittenden County; the highest water-level altitude measured was 368 feet above the National Geodetic Vertical Datum of 1929 on Crowleys Ridge in Clay County. Hydrographs from 28 wells with historical water levels from 1986 to 2006 were evaluated using linear regression to calculate the annual rise or decline. All 28 wells showed an annual decline from 1986 to 2006. Craighead, Greene, Mississippi, and Poinsett Counties have mean annual declines from 0.27 to 1.00 feet per year. Crittenden, Lee, and St. Francis Counties have mean annual declines from 1.39 to 1.64 feet per year.

Scientific Investigations Report↗
USGS1996

Hydrogeology of, and simulation of ground-water flow in, a mantled carbonate-rock system, Cumberland Valley, Pennsylvania

The U.S. Geological Survey conducted a study in a highly productive and complex regolith-mantled carbonate valley in the northeastern part of the Cumberland Valley, Pa., as part of its Appalachian Valleys and Piedmont Regional Aquifer-system Analysis program. The study was designed to quantify the hydrogeologic characteristics and understand the ground-water flow system of a highly productive and complex thickly mantled carbonate valley. The Cumberland Valley is characterized by complexly folded and faulted carbonate bedrock in the valley bottom, by shale and graywacke to the north, and by red-sedimentary and diabase rocks in the east-southeast. Near the southern valley hillslope, the carbonate rock is overlain by wedge-shaped deposit of regolith, up to 450 feet thick, that is composed of residual material, alluvium, and colluvium. Locally, saturated regolith is greater than 200 feet thick. Seepage-run data indicate that stream reaches, near valley walls, are losing water from the stream, through the regolith, to the ground-water system. Results of hydrograph-separation analyses indicate that base flow in stream basins dominated by regolith-mantled carbonate rock, carbonate rock, and carbonate rock and shale are 81.6, 93.0, and 67.7 percent of total streamflow, respectively. The relative high percentage for the regolith-mantled carbonate-rock basin indicates that the regolith stores precipitation and slowly, steadily releases this water to the carbonate-rock aquifer and to streams as base flow. Anomalies in water-table gradients and configuration are a result of topography and differences in the character and distribution of overburden material, permeability, rock type, and geologic structure. Most ground-water flow is local, and ground water discharges to nearby springs and streams. Regional flow is northeastward to the Susquehanna River. Average-annual water budgets were calculated for the period of record from two continuous streamflow-gaging stations. Average-annual precipitation range from 39.0 to 40.5 inches, and averages about 40 inches for the model area. Average-annual recharge, which was assumed equal to the average-annual base flow, ranged from 12 inches for the Conodoguinet Creek, and 15 inches for the Yellow Breeches Creek. The thickly-mantled carbonate system was modeled as a three- dimensional water-table aquifer. Recharge to, ground-water flow through, and discharge from the Cumberland Valley were simulated. The model was calibrated for steady-state conditions using average recharge and discharge data. Aquifer horizontal hydraulic conductivity was calculated from specific-capacity data for each geologic unit in the area. Particle-tracking analyses indicate that interbasin and intrabasin flows of groundwater occur within the Yellow Breeches Creek Basin and between the Yellow Breeches and Conodoguinet Creek Basins.

Pennsylvania↗
USGS2024

Geology, coastal geomorphology, and soils of eastern Santa Cruz Island (Limuw), Channel Islands National Park, California, USA

This one-day field trip explores northeastern Santa Cruz Island ( Limuw , in native Chumash), a part of Channel Islands National Park, USA. The geomorphology of eastern Santa Cruz Island has been controlled largely by active tectonics and sea-level fluctuations. The bedrock is Miocene volcanic rock overlain by Miocene shale and siltstone. The island has experienced Quaternary uplift, perhaps due to movement along an offshore thrust fault. Smaller faults are exposed in sea cliffs and have displaced Miocene rocks. Superimposed upon island uplift, there have been Quaternary sea-level fluctuations from interglacial-glacial climate changes. Interglacial high-sea stands are recorded as marine terraces. The last major interglacial period, ~120,000 years ago, left only small remnants of marine terraces. Most evidence of this high-sea stand was eroded away in the Holocene. However, a prominent marine terrace is preserved at 75–120 m above sea level. Some fossil mollusks from the deposits of this terrace, probably reworked, have given ages as old as Pliocene, but most yield ages of 2.6–2.0 Ma. The age and elevation of this terrace indicate a very low rate of tectonic uplift, similar to nearby Anacapa Island. A low uplift rate explains the absence or scarcity of younger terraces, including that of the last interglacial period. Low stands of sea (glacial periods) exposed the insular shelf, rich in carbonate skeletal sand. During glacial periods, these sands were entrained by the wind, deposited as dunes on marine terraces, and cemented into eolianite. Clay-rich Vertisols with silt mantles have developed on eolianites and terraces of the island, partly from in situ weathering, but also from inputs of Mojave Desert dust during Santa Ana wind events. This guide includes stops at Scorpion Anchorage, Cavern Point, and Potato Harbor. It provides insights into the bedrock, coastal geomorphology, fossiliferous marine terraces, eolianite, Vertisols, and the three formations on eastern Santa Cruz Island: the Santa Cruz Island Volcanics, the Monterey Formation, and the Potato Harbor Formation.

California↗
USGS2015

Flooding in the Northeastern United States, 2011

Flooding in the Northeastern United States during 2011 was widespread and record setting. This report summarizes peak streamflows that were recorded by the U.S. Geological Survey (USGS) during separate flooding events in February, March, April, May, July, August, and September. The flooding of late April, which combined snowmelt and heavy rain and the floods associated with the tropical storms of late August and September, were the most severe and widespread. Precipitation totals from March to May for Pennsylvania, New York, and Vermont were documented as being the highest totals in 117 years of record. In late August, the heavy rains associated with Hurricane Irene produced widespread flooding in many parts of the Northeastern United States, which resulted in damage estimates in excess of $7 billion and approximately 45 deaths. In September, Tropical Storm Lee produced 6–12 inches of rain in parts of the Northeastern United States adding to the growing total of record peak streamflows set in 2011. The annual exceedance probability (AEP) for 327 streamgages in the Northeastern United States were computed using annual peak streamflow data through 2011 and are included in this report. The 2011 peak streamflow for 129 of those streamgages was estimated to have an AEP of less than or equal to 1 percent. Almost 100 of these peak streamflows were a result of the flooding associated with Hurricane Irene in late August 2011. More extreme than the 1-percent AEP, is the 0.2-percent AEP. The USGS recorded peak streamflows at 31 streamgages that equaled or exceeded the estimated 0.2-percent AEP during 2011. Collectively, the USGS recorded peak streamflows having estimated AEPs of less than 1 percent in Connecticut, Delaware, Maine, Maryland, Massachusetts, Ohio, Pennsylvania, New Hampshire, New Jersey, New York, and Vermont and new period-of-record peak streamflows were recorded at more than 180 streamgages resulting from the floods of 2011.

Connecticut, Delaware, Maine, Maryland, Massachuse↗
USGS1970

Ground-water resources of Nelson County, northeastern North Dakota

This investigation is part of a Statewide program to determine the location and extent of the ground-water reservoirs (aquifers); to evaluate the occurrence and movement of ground water within these aquifers, including the sources of recharge and discharge; and to determine the chemical quality of the ground water. Nelson County covers an area of approximately 1,000 square miles in northeastern North Dakota. The study, which began in July 1967, has been made cooperatively by the U.S. Geological Survey, the North Dakota State Water Commission, the North Dakota Geological Survey, and the Nelson County Water Management District. The final results of the study will be published in three parts by the cooperating State agencies.

Hydrologic Atlas↗