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At least 919 records · Page 51Linked to original sources
USGS2007

Ground-water age and quality in the High Plains Aquifer near Seward, Nebraska, 2003-04

The U.S. Geological Survey, in cooperation with the City of Seward, Nebraska, conducted a study of ground-water age and quality to improve understanding of: (1) traveltimes from recharge areas to public-supply wells, (2) the effects of geochemical reactions in the aquifer on water quality, and (3) how water quality has changed historically in response to land-use practices. Samples were collected from four supply wells in the Seward west well field and from nine monitoring wells along two approximate ground-water flow paths leading to the well field. Concentrations of three different chlorofluorocarbons (CFC-12, CFC-11, and CFC-113), sulfur hexafluoride (SF 6 ), and ratios of tritium ( 3 H) to helium-3 ( 3 He) isotope derived from radioactive decay of 3H were used to determine the apparent recharge age of ground-water samples. Age interpretations were based primarily on 3 H/ 3 He and CFC-12 data. Estimates of apparent ground-water age from tracer data were complicated by mixing of water of different ages in 10 of the 13 ground-water samples collected. Apparent recharge dates of unmixed ground-water samples or mean recharge dates of young fractions of mixed water in samples collected from monitoring wells ranged from 1985 to 2002. For monitoring-well samples containing mixed water, the fraction of the sample composed of young water ranged from 26 to 77 percent of the sample. Apparent mean recharge dates of young fractions in samples collected from four supply wells in the Seward west well field ranged from about 1980 to 1990. Estimated fractions of the samples composed of young water ranged from 39 to 54 percent. It is implicit in the mixing calculations that the remainder of the sample that is not young water is composed of water that is more than 60 years old and contains no detectable quantities of modern atmospheric tracers. Estimated fractions of the mixed samples composed of "old" water ranged from 23 to 74 percent. Although alternative mixing models can be used to interpret the results, the mean age and mixing fractions from the primary mixing models used were fairly similar. Relations of ground-water age and nitrate concentrations to depth were not consistent across the study area. In some well nests, more young water and nitrate were present near the bottom than in the middle of the aquifer. These results probably reflect pumping from irrigation and supply wells, which are screened primarily in the lower part of the aquifer, and draw younger water downward in the aquifer. Substantial mixing probably occurs because the aquifer is relatively thin (50 feet) and has a relatively high density of wells (about five pumping wells per square mile). The most reliable estimate of horizontal traveltimes based on differences in ground-water ages between a shallow monitoring well at the upgradient end of the northwest well transect and the deep well at the downgradient end of the well transect was 9 years to travel a distance of about 2 miles. The general similarity of ages at similar depths between different well nests is consistent with the fact that horizontal flow in the aquifer is relatively rapid. Concentrations of nitrate (as nitrogen) in untreated ground-water samples from supply wells in the well field were larger than the U.S. Environmental Protection Agency Maximum Contaminant Level for drinking water of 10 mg/L (milligrams per liter), ranging from 11.3 to 13.5 mg/L. It is unlikely that nitrate concentrations in the aquifer near the Seward west well field are decreased by denitrification in the aquifer due to oxic geochemical conditions that preclude this reaction. Nitrate concentrations coupled with water recharge dates were compared to historical estimated fertilizer application in an attempt to reconstruct historical trends in ground-water nitrate concentrations and their relation to land-use practices. Nitrate concentrations in young-water fractions, after adjustment for mixing, may be decreasing over apparent recharge dates of 1980 to 2002, corresponding to a period of generally decreasing nitrogen fertilizer applications.

Nebraska↗
USGS2008

Hydrogeology, Water Chemistry, and Factors Affecting the Transport of Contaminants in the Zone of Contribution of a Public-Supply Well in Modesto, Eastern San Joaquin Valley, California

Ground-water chemistry in the zone of contribution of a public-supply well in Modesto, California, was studied by the U.S. Geological Survey National Water Quality Assessment (NAWQA) Program's topical team for Transport of Anthropogenic and Natural Contaminants (TANC) to supply wells. Twenty-three monitoring wells were installed in Modesto to record baseline hydraulic information and to collect water-quality samples. The monitoring wells were divided into four categories that represent the chemistry of different depths and volumes of the aquifer: (1) water-table wells were screened between 8.5 and 11.7 m (meter) (28 and 38.5 ft [foot]) below land surface (bls) and were within 5 m (16 ft) of the water table; (2) shallow wells were screened between 29 and 35 m (95 and 115 ft) bls; (3) intermediate wells were screened between 50.6 and 65.5 m (166 and 215 ft) bls; and (4) deep wells are screened between 100 to 106 m (328 and 348 ft) bls. Inorganic, organic, isotope, and age-dating tracers were used to characterize the geochemical conditions in the aquifer and understand the mechanisms of mobilization and movement of selected constituents from source areas to a public-supply well. The ground-water system within the study area has been significantly altered by human activities. Water levels in monitoring wells indicated that horizontal movement of ground water was generally from the agricultural areas in the northeast towards a regional water-level depression within the city in the southwest. However, intensive pumping and irrigation recharge in the study area has caused large quantities of ground water to move vertically downward within the regional and local flow systems. Analysis of age tracers indicated that ground-water age varied from recent recharge at the water table to more than 1,000 years in the deep part of the aquifer. The mean age of shallow ground water was determined to be between 30 and 40 years. Intermediate ground water was determined to be a mixture of modern (Post-1950) and old (Pre-1950) ground water. As a result, concentrations of age tracers were detectable but diluted by older ground water. Deep ground water generally represented water that was recharged under natural conditions and therefore had much older ages. Ground water reaching the public-supply well was a mixture of older intermediate and deep ground water and young shallow ground water that has been anthropogenically-influenced to a greater extent than intermediate ground water. Uranium and nitrate pose the most significant threat to the quality of water discharged from the public-supply well. Although pesticides and VOCs were present in ground water from the public-supply well and monitoring wells, currently concentrations of these contaminants are generally less than one-hundredth the concentration of drinking water standards. In contrast, both uranium and nitrate were above half the concentration of drinking water standards for public-supply well samples, and were above drinking water standards for several water-table and shallow monitoring wells. Shallow ground water contributes roughly 20 percent of the total flow to the public-supply well and was the entry point of most contaminants reaching the public-supply well. Naturally-occurring uranium, which is commonly adsorbed to aquifer sediments, was mobilized by oxygen-rich, high-alkalinity water, causing concentrations in some monitoring wells to be above the drinking-water standard of 30 ug/L (microgram per liter). Adsorption experiments, sediment extractions, and uranium isotopes indicated uranium in water-table and shallow ground water was leached from aquifer sediments. Uranium is strongly correlated to bicarbonate concentrations (as measured by alkalinity) in ground water. Bicarbonate can effectively limit uranium adsorption to sediments. As a result, continued downward movement of high-alkalinity, oxygen-rich ground water will likely lead to larger portions of the aquifer having

Scientific Investigations Report↗
USGS2020

Geochemical assessment of groundwater in the Big Chino subbasin, Arizona, 2011–18

A geochemical characterization of groundwater in the Big Chino subbasin of Arizona was conducted by the U.S. Geological Survey, in cooperation with the City of Prescott, the Town of Prescott Valley, and the Salt River Project, to understand groundwater evolution through the study area and the source of water to springs along the gaining reach of the Verde River just downstream from its confluence with Granite Creek. Samples were collected between 2011 and 2018 in groundwater wells completed in basin-fill and carbonate aquifers and at selected springs, including two discrete springs discharging along the aforementioned stretch of the Verde River. Five newly installed monitoring wells completed in the carbonate aquifer were sampled in 2018. Water-quality results obtained from these samples include the first known geochemical data for carbonate groundwater beneath the basin-fill in the Big Chino subbasin downgradient from Walnut Creek near Paulden, Arizona, as well as other parts of the study area without previous data. Groundwater samples were collected and analyzed for major ions, arsenic, nutrients, stable isotopes of oxygen and hydrogen (δ 18 O and δ 2 H), strontium isotopes ( 87 Sr/ 86 Sr), carbon-14, isotopes of carbon (δ 13 C), and noble gases. Significant differences in groundwater geochemistry between the basin-fill and carbonate aquifers were driven primarily by higher pH, tritium, and δ 18 O and δ 2 H in the basin-fill aquifer samples and higher specific conductance and higher concentrations of calcium, sodium, bicarbonate, fluoride, and arsenic in the carbonate aquifer samples. All but one sample from the carbonate aquifer and two samples from the basin-fill aquifer exceeded the U.S. Environmental Protection Agency (EPA) drinking water standard for arsenic of 10 micrograms per liter. One basin-fill aquifer sample exceeded the EPA drinking water standard for fluoride of 4 milligrams per liter, and one carbonate aquifer sample exceeded the EPA secondary drinking water standard for fluoride of 2 milligrams per liter. A component of modern groundwater recharged following aboveground nuclear testing beginning in the mid-1950s is present in some basin-fill and spring groundwater from this study. Groundwater that can be dated using radiocarbon decay is also present in the study area, with four groundwater samples indicating possible recharge during the Pleistocene with groundwater ages ranging from approximately 34,600 to 13,300 years before present. Other groundwater sampled during this study that can dated using radiocarbon decay ranged in age from about 7,500 to 1,100 years before present, indicating possible recharge during the Holocene. The gaining reach of the Verde River downstream from the confluence with Granite Creek shows areal changes in temperature, pH, and specific conductance, indicating multiple zones of groundwater input. Surface-water samples for analyses of δ 18 O and δ 2 H have been collected at the Verde River near Paulden, Ariz. streamgage (09503700) during discharge measurements since 2009, and a trend analysis of the δ 18 O and δ 2 H data indicated no significant trend exists for the 10-year period of record. Additional groundwater samples from the carbonate aquifer beneath the basin-fill upgradient and downgradient from Walnut Creek would provide valuable information to understand groundwater evolution along the Big Chino subbasin.

Arizona↗
USGS2007

Sedimentation History of Halfway Creek Marsh, Upper Mississippi River National Wildlife and Fish Refuge, Wisconsin, 1846-2006

The history of overbank sedimentation in the vicinity of Halfway Creek Marsh near La Crosse, Wis., was examined during 2005?06 by the U.S. Geological Survey and University of Wisconsin?Madison as part of a broader study of sediment and nutrient loadings to the Upper Mississippi River bottomlands by the U.S. Environmental Protection Agency, U.S. Fish and Wildlife Service, and U.S. Geological Survey. Historical sedimentation patterns and rates were interpreted from field-scale topographic surveys and sediment cores collected from the marsh and upstream flood plains. Historical maps and aerial photographs were used to establish the timing of disturbances and to document changes in channel patterns after Euro-American settlement (post 1846). Episodic overbank sedimentation patterns and rates were linked to watershed agricultural activity, large floods, artificial levee construction, channel alterations, and dam failures over the past 160 years. These forces affected sedimentation on and between levees, the development of alluvial fans and flood-plain splays, and the general pattern of flood-plain sedimentation through the upper and lower marsh. Historical overbank deposits, episodically deposited after about 1860, are as much as 6 feet thick in the upper marsh and as much as 4 feet thick in the lower marsh, representing a total volume of approximately 1.8 million cubic yards. These stratified deposits consist of multiple layers of silt and clay, very fine to fine sand, and some medium to very coarse sand. Coarse-grained deposits are associated with flood-plain splays caused by breaches in artificial levees during large floods. Estimated sedimentation rates were highest from 1919 to 1936 [26,890 cubic yards per year (yd3/yr)] and exceeded by about 30 times the 1846?85 rate of 920 yd3/yr and exceeded by 7 times the 1994?2006 rate of 3,740 yd3/yr. The 1994?2006 sedimentation rate was the lowest since Euro-American settlement, but natural levees along the 1994?2006 channel of Halfway Creek through the lower marsh continued to form and are currently (2006) about 1 foot higher than the surrounding marsh. Natural levee building in the lower marsh from 1994?2006 was accentuated by the lack of overbank sediment storage in the upper marsh. The historical storage of sediment in the upper and lower marsh affects modern streamflow and sediment transport processes of Halfway Creek and Sand Lake Coulee through the marsh, and it also affects marsh vegetation and wildlife habitat. Results from this investigation will help improve the understanding of how past overbank sedimentation patterns continue to influence modern and future water quality, sediment transport, nutrient loads, and water-related resources in riparian habitats common to the Upper Mississippi River National Wildlife and Fish Refuge.

Scientific Investigations Report↗
USGS2012

Hydrogeology, water chemistry, and transport processes in the zone of contribution of a public-supply well in Albuquerque, New Mexico, 2007-9

The National Water-Quality Assessment Program (NAWQA) of the U.S. Geological Survey began a series of groundwater studies in 2001 in representative aquifers across the Nation in order to increase understanding of the factors that affect transport of anthropogenic and natural contaminants (TANC) to public-supply wells. One of 10 regional-scale TANC studies was conducted in the Middle Rio Grande Basin (MRGB) in New Mexico, where a more detailed local-scale study subsequently investigated the hydrogeology, water chemistry, and factors affecting the transport of contaminants in the zone of contribution of one 363-meter (m) deep public-supply well in Albuquerque. During 2007 through 2009, samples were collected for the local-scale study from 22 monitoring wells and 3 public-supply (supply) wells for analysis of major and trace elements, arsenic speciation, nutrients, dissolved organic carbon, volatile organic compounds (VOCs), dissolved gases, stable isotopes, and tracers of young and old water. To study groundwater chemistry and ages at various depths within the aquifer, the monitoring wells were divided into three categories: (1) each shallow well was screened across the water table or had a screen midpoint within 18.3 m of the water level in the well; (2) each intermediate well had a screen midpoint between about 27.1 and 79.6 m below the water level in the well; and (3) each deep well had a screen midpoint about 185 m or more below the water level in the well. The 24-square-kilometer study area surrounding the "studied supply well" (SSW), one of the three supply wells, consists of primarily urban land within the MRGB, a deep alluvial basin with an aquifer composed of unconsolidated to moderately consolidated deposits of sand, gravel, silt, and clay. Conditions generally are unconfined, but are semiconfined at depth. Groundwater withdrawals for public supply have substantially changed the primary direction of flow from northeast to southwest under predevelopment conditions, to west to east under modern conditions. Analysis of age tracers indicates that groundwater from most sampled wells is dominated by old (pre-1950) water, ranging in mean age from about 4,000 years to more than 22,000 years, but includes a fraction of young (post-1950) recharge. Patterns in chemical and isotopic data are consistent with the conclusions that shallow groundwater in the area typically includes a fraction that evaporated prior to recharge and (or) flushed accumulated solutes out of the unsaturated zone during recharge, and that shallow groundwater has mixed to deeper parts of the aquifer, which receives recharge mainly by seepage from the Rio Grande. Among shallow and intermediate wells that produced water with a fraction of young recharge, that fraction ranged between 1.5 and 46 percent. Samples from the two deep wells had groundwater ages exceeding 18,000 years, with no fraction of young recharge. Two supply wells (including the SSW) had a fraction of young recharge, which ranged between about 3 and 11 percent, despite mean groundwater ages exceeding 10,000 years. The fraction of young recharge to the SSW varied seasonally, probably because seasonal pumping patterns affected local hydraulic gradients and (or) because of flow through the well bore when the SSW is not pumping. Well-bore flow data collected during winter (low-pumping season) indicated that about 61 percent of the water pumped from the SSW entered the well from the intermediate part of the aquifer, and that the remaining 39 percent entered from the deep part of the aquifer. Volatile organic compounds (VOCs) were detected in samples from most shallow and intermediate monitoring wells and from two of three supply wells, including the SSW. Detected VOCs were primarily chlorinated solvents or their degradation products. Many of the wells in which most of these VOCs were detected are located near known sites of solvent contamination that were targeted for sampling because trichloroethylene (TCE) and cis-1,2-dichloroethylene had been detected in the SSW, and several of these wells may have become contaminated at least partly because of enhanced vertical migration associated with the pumping of and (or) direct migration down deep well bores. Except for TCE in the sample from a shallow monitoring well, all detections of VOCs were at concentrations below Maximum Contaminant Levels (MCLs) set by the U.S. Environmental Protection Agency. Concentrations of all VOCs detected in the supply wells were less than one-tenth of the corresponding MCLs. However, the presence of VOCs in all but deep groundwater, including the detection of chloroform (a chlorination byproduct) in several shallow wells, indicates that groundwater in the study area commonly is affected by human activities, even to substantial depths. The only natural contaminant detected at concentrations near or above its MCL was arsenic, which has been detected at elevated concentrations across broad areas of the MRGB. Concentrations of arsenic, present primarily as arsenate, exceeded the MCL of 10 micrograms per liter (μg/L) in water from the two deep wells (one of which had the highest concentration, 35 μg/L), from one intermediate well, and from two supply wells, including the SSW. Water-quality and solid-phase data from this study are consistent with elevated arsenic concentrations in groundwater being related to pH-dependent desorption of arsenic from ferric oxyhydroxides in sediments in deep parts of the aquifer. Concentrations of nitrate ranged between 1.3 and 5.4 milligrams per liter (mg/L) in water from shallow wells screened across the water table, but were less than 0.9 mg/L in water from all but one deeper well. Nitrogen isotopes and chloride/bromide ratios for shallow wells were consistent with natural soil nitrogen. Nitrate concentrations and nitrogen isotopes indicated that denitrification is occurring at intermediate aquifer depths, and that the progress of the denitrification reaction typically is greatest for wells that include a fraction of groundwater associated with particular recharge sources or with known sites of contamination contributing organic compounds that can provide a carbon source for microbial respiration. Overall, hydrologic and chemical data from the study area indicate that young recharge is reaching the aquifer across broad areas and is migrating from shallow to intermediate depths of the aquifer as a result of mixing that is associated with human development of groundwater. Consequently, groundwater that human activities in the urban study area have affected is present at depths that are within the screened intervals of public-supply wells, resulting in detections of VOCs and implying greater vulnerability to anthropogenic contamination than might be assumed based on the dominantly old age of the regional groundwater. However, the fractions of old groundwater that public-supply wells produce substantially dilute the anthropogenic contaminants, while contributing natural contaminants (primarily arsenic) to the wells. Based on data from the SSW, vulnerability of public-supply wells to natural and anthropogenic contaminants in the area changes through time, including with seasonal changes in pumping stresses that alter the fractions of young and old water being contributed to wells.

New Mexico↗
USGS2024

The 3D National Topography Model Call for Action—Part 1. The 3D Hydrography Program

The U.S. Geological Survey is initiating the 3D Hydrography Program (3DHP), the first systematic remapping of the Nation’s surface waters since the original 1:24,000-scale topographic mapping program was active from 1947 to 1992. Building on decades of experience maintaining the National Hydrography Dataset (NHD), the Watershed Boundary Dataset (WBD), and the NHDPlus High Resolution (NHDPlus HR), the 3DHP will completely refresh the Nation’s hydrography data and improve discovery and sharing of water-related data. The design of the 3DHP is based on the results of a study that estimated that the fully implemented program would have the potential to provide more than $1 billion in benefits to Federal, State, Tribal, Territorial, and local governments and to private and nonprofit organizations every year, in addition to myriad societal benefits. The 3DHP would directly support better decision making regarding water resources by providing more accurate, complete, and integrated information than is currently available. The 3DHP datasets will include a three-dimensional (3D) hydrography network generated from and integrated with elevation data from the 3D Elevation Program (3DEP) to better represent stream gradients and channel conditions, along with waterbodies, hydrologic units, hydrologically enhanced elevation and other surfaces, and more consistent and accurate attributes. The 3DHP datasets will inherit key attributes of the NHD, WBD, and NHDPlus HR, and they also will include new attributes and links to other data such as the U.S. Fish and Wildlife Service National Wetlands Inventory, groundwater data, and engineered hydrologic systems such as stormwater networks. The 3DHP will be designed to provide a set of open and interoperable web-based tools, maps, and data catalogs, creating a robust system for users to reference their information about water; the system elements are collectively referred to as the “infostructure.” The 3DHP and the infostructure can provide a foundational geospatial underpinning for the Internet of Water, a community-based effort to modernize tools and technologies to share water data. As proposed, the 3DHP would begin providing products and services to the public in 2024.

Circular↗
USGS2020

Louisiana Barrier Island Comprehensive Monitoring Program: Mapping habitats in beach, dune, and intertidal environments along the Louisiana Gulf of Mexico shoreline, 2008 and 2015–16

Barrier islands, headlands, and coastal shorelines provide numerous valuable ecosystem goods and services, including storm protection and erosion control for the mainland, habitat for fish and wildlife, salinity regulation in estuaries, carbon sequestration in marshes, and areas for recreation and tourism. These coastal features are dynamic environments because of their position at the land-sea interface. Storms, wave energy, tides, currents, and relative sea-level rise are powerful forces that shape local geomorphology and habitat distribution. In order to make more informed decisions, coastal resource managers require insights into how these dynamic systems are changing through time. In 2005, Louisiana’s Coastal Protection and Restoration Authority, in partnership with the University of New Orleans and the U.S. Geological Survey, developed the Barrier Island Comprehensive Monitoring (BICM) Program. The goal of the BICM Program is to develop long-term datasets for habitat coverage, shoreline assessments, shoreline position, topobathymetric changes, and sediment characterization to assist with planning, designing, evaluating, and maintaining current and future barrier shorelines. The overall objectives of the study described in this report were to (1) map habitats for 2008 and 2015–16 for BICM coastal reaches and (2) map habitat change between these two time periods. This report highlights the second phase of habitat analyses for the BICM Program. This work builds on a previous habitat analysis conducted by the University of New Orleans, which included the development of habitat maps for 1996/1998, 2001, 2004, and 2005, along with habitat change maps. For this current effort, a new 15-class habitat scheme was developed from the original BICM scheme to further delineate various dune habitats, including meadow habitat found along the backslopes of dunes, to distinguish between marsh and mangrove, and to distinguish between beach and unvegetated barrier flat habitats. Additionally, a geographic object-based image analysis-based mapping framework was used to incorporate relative topography and address elevation uncertainty in light detection and ranging data to assist with mapping dune and intertidal habitats. For the entire BICM region, the area experiencing a change in a land/water category (that is, land gain or land loss) was 3.4 percent, of which, 59.2 percent was land gain and 40.8 percent was land loss. Areal coverages of meadow, mangrove, scrub/shrub, and vegetated dune increased from 2008 to 2015–16, whereas areal coverages of beach, grassland, and intertidal decreased. The decrease in intertidal, however, was largely due to differing water levels in the orthophotography between the two time periods. Regional analyses of habitat coverage and habitat change captured the dynamic nature of these systems and the effects of restoration efforts, most notably in the Late Lafourche Delta, Modern Delta, and Chandeleur Islands regions. For instance, in the Modern Delta region there was a marked increase in unvegetated flat, meadow, mangrove, scrub/shrub, beach, unvegetated dune, and vegetated dune. As a result, this region experienced the highest percent change for land/water classes (6.6 percent) with land gain accounting for much of this change (70.8 percent). In contrast, the Acadiana Bays region had the highest relative percent loss of all regions. The region had a percent change for land/water classes of 2.8 percent, of which, 79.7 percent was land loss. The results of this study provide information about the areal coverage and distribution of habitats for two recent time periods and change over about an 8-year period. These data can be used to evaluate changes along the Louisiana Gulf of Mexico shoreline, including gradual changes caused by coastal processes, restoration actions, and (or) episodic events, such as hurricanes and extreme storms.

Louisiana↗
USGS1972

Reconnaissance engineering geology of the Haines area, Alaska, with emphasis on evaluation of earthquake and other geologic hazards

The Alaska earthquake of March 27, 1964, brought into sharp focus the need for engineering geologic studies in urban areas. Study of the Haines area constitutes an integral part of an overall program to evaluate earthquake and other geologic hazards in most of the larger Alaska coastal communities. The evaluations of geologic hazards that follow, although based only upon reconnaissance studies and, therefore, subject to revision, will provide broad guidelines useful in city and land-use planning. It is hoped that the knowledge gained will result in new facilities being built in the best possible geologic environments and being designed so as to minimize future loss of life and property damage. Haines, which is in the northern part of southeastern Alaska approximately 75 miles northwest of Juneau, had a population, of about 700 people in 1970. It is built at the northern end of the Chilkat Peninsula and lies within the Coast Mountains of the Pacific Mountain system. The climate is predominantly marine and is characterized by mild winters and cool summers. The mapped area described in this report comprises about 17 square miles of land; deep fiords constitute most of the remaining mapped area that is evaluated in this study. The Haines area was covered by glacier ice at least once and probably several times during the Pleistocene Epoch. The presence of emergent marine deposits, several hundred feet above sea level, demonstrates that the land has been uplifted relative to sea level since the last major deglaciation of the region about 10,000 years ago. The rate of relative uplift of the land at Haines during the past 39 years is 2.26 cm per year. Most or all of this uplift appears to be due to rebound as a result of deglaciation. Both bedrock and surficial deposits are present in the area. Metamorphic and igneous rocks constitute the exposed bedrock. The metamorphic rocks consist of metabasalt of Mesozoic age and pyroxenite of probable early middle Cretaceous age. The igneous rocks consist of diorite and quartz diorite (tonalite) of Cretaceous age. Sedimentary rocks of Tertiary age may be present in the mapped area but are not exposed. The surficial deposits of Quaternary age,-have been divided into the following map units on the basis of time Of deposition, mode of origin, and grain size: (1) undifferentiated drift deposits, (2) outwash and Ice-contact deposits; (3) elevated fine-grained marine deposits, (4) elevated shore and delta deposits, (5) alluvial fan deposits, (6) colluvial deposits, (7) modern beach deposits, (8) Chilkat River flood-plain and delta deposits, and (9) manmade fill. Offshore deposits are described but are not mapped. Southeastern Alaska lies within the tectonically active belt that rims the northern Pacific Basin and has been active since at least early Paleozoic time. The outcrop pattern is the result of late Mesozoic and Tertiary deformational, metamorphic, and intrusive events. Large-scale faulting has been common. The two most prominent inferred fault systems in southeastern Alaska and surrounding regions are: (1) The Denali fault system and (2) the Fairweather-Queen Charlotte Islands fault system. In the general area of Haines, rocks of Mesozoic age northeast of Chilkat River have a simple monoclinal structure. Paleozoic-Mesozoic rocks southwest of Chilkat River are gently to rather complexly folded. Several major and numerous minor faults probably transect the general area of Haines but their exact location and character can only be inferred because their traces are coincident to the long axes of fiords and river valleys, where they are concealed by water or by valley-floor deposits. Inferred faults in or near the Haines mapped area are: (1) Chilkat River fault, (2) Chilkoot fault, (3) Takhin fault, and (4) faults in the saddle area at Haines. Southeastern Alaska lies in one of the two most seismically active zones in Alaska, a State where 6 percent of the world's shallow earthqua

Open-File Report↗
USGS1998

Weakness of the lower continental crust: A condition for delamination, uplift, and escape

We discuss three interconnected processes that occur during continental compression and extension: delamination of the lower crust and sub-crustal lithosphere, escape tectonics (i.e., lateral crustal flow), and crustal uplift. We combine calculations of lithospheric viscosity–depth curves with geologic observations and seismic images of the deep crust to infer the mechanisms controlling these processes. The basic driving force for delamination is the negative buoyancy (in some regions) of the continental lower crust and sub-crustal lithosphere with respect to the warm, mobile asthenosphere. A phase transformation in the lower crust from mafic granulite facies to eclogite may be important for providing negative buoyancy. Where negative buoyancy exists, the onset of delamination is mainly a question of the presence of a suitable decoupling zone between the denser lithosphere and the lighter upper and middle crust. We estimate the depth to potential decoupling zones by calculating lithospheric viscosity–depth curves based on reasonable geotherms and models of lithospheric composition. Low-viscosity zones occur at three depths: (1) at the base of the felsic (upper) crust; (2) within the lower crust; and (3) several tens of kilometers below the Moho. The commonly observed absence of a high-velocity (>6.8 km/s) lower crustal layer beneath extended crust may be explained by delamination wherein decoupling occurs at the top of the lower crust. In addition to being zones of potential decoupling, crustal low-viscosity zones are avenues for lateral crustal flow, a process that is often referred to as crustal escape (e.g., eastern Tibetan Plateau). The third process addressed here, crustal uplift, is mainly found in compressional environments and can be related to mature (i.e., complete or nearly complete) delamination and/or a thick low-viscosity lower crust. Mature delamination generates crustal uplift as the sinking, dense lithosphere is replaced by the mobilized hot asthenosphere. A very different mechanism of uplift is associated with some continental high plateaus, where a high convergence rate and the lateral intrusion of cold, rigid shield crust into warm, low-viscosity orogenic crust acts like a solid piston moving into hydraulic fluid. The displacement of the low-viscosity crustal `fluid' generates broad plateau uplifts. Modern examples are the intrusion of the Indian shield into the Tibetan Plateau and the Brazilian shield into the Andes. All of these processes, delamination, tectonic escape, and uplift are interconnected and are related to weakness in the lower crust during continental compression and extension.

Tectonophysics↗
USGS2008

Geomorphic map of Worcester County, Maryland, interpreted from a LIDAR-based, digital elevation model

A recently compiled mosaic of a LIDAR-based digital elevation model (DEM) is presented with geomorphic analysis of new macro-topographic details. The geologic framework of the surficial and near surface late Cenozoic deposits of the central uplands, Pocomoke River valley, and the Atlantic Coast includes Cenozoic to recent sediments from fluvial, estuarine, and littoral depositional environments. Extensive Pleistocene (cold climate) sandy dune fields are deposited over much of the terraced landscape. The macro details from the LIDAR image reveal 2 meter-scale resolution of details of the shapes of individual dunes, and fields of translocated sand sheets. Most terrace surfaces are overprinted with circular to elliptical rimmed basins that represent complex histories of ephemeral ponds that were formed, drained, and overprinted by younger basins. The terrains of composite ephemeral ponds and the dune fields are inter-shingled at their margins indicating contemporaneous erosion, deposition, and re-arrangement and possible internal deformation of the surficial deposits. The aggregate of these landform details and their deposits are interpreted as the products of arid, cold climate processes that were common to the mid-Atlantic region during the Last Glacial Maximum. In the Pocomoke valley and its larger tributaries, erosional remnants of sandy flood plains with anastomosing channels indicate the dynamics of former hydrology and sediment load of the watershed that prevailed at the end of the Pleistocene. As the climate warmed and precipitation increased during the transition from late Pleistocene to Holocene, dune fields were stabilized by vegetation, and the stream discharge increased. The increased discharge and greater local relief of streams graded to lower sea levels stimulated down cutting and created the deeply incised valleys out onto the continental shelf. These incised valleys have been filling with fluvial to intertidal deposits that record the rising sea level and warmer, more humid climate in the mid-Atlantic region throughout the Holocene. Thus, the geomorphic details provided by the new LIDAR DEM actually record the response of the landscape to abrupt climate change. Holocene trends and land-use patterns from Colonial to modern times can also be interpreted from the local macro- scale details of the landscape. Beyond the obvious utility of these data for land-use planning and assessments of resources and hazards, the new map presents new details on the impact of climate changes on a mid-latitude, outer Coastal plain landscape.

Maryland↗
USGS1973

Stratigraphy and geologic history of the Montana group and equivalent rocks, Montana, Wyoming, and North and South Dakota

During Late Cretaceous time a broad north-trending epicontinental sea covered much of the western interior of North America and extended from the Gulf of Mexico to the Arctic Ocean. The sea was bounded on the west by a narrow, unstable, and constantly rising cordillera which extended from Central America to Alaska and which separated the sea from Pacific oceanic waters. The east margin of the sea was bounded by the low-lying stable platform of the central part of the United States. Rocks of the type Montana Group in Montana and equivalent rocks in adjacent States, which consist of eastward-pointing wedges of shallow-water marine and nonmarine strata that enclose westward-pointing wedges of fine-grained marine strata, were deposited in and marginal to this sea. These rocks range in age from middle Santonian to early Maestrichtian and represent a time span of about 14 million years. Twenty-nine distinctive ammonite zones, each with a time span of about half a million years, characterize the marine strata. Persistent beds of bentonite in the transgressive part of the Claggett and Bearpaw Shales of Montana and equivalent rocks elsewhere represent periods of explosive volcanism and perhaps concurrent subsidence along the west shore in the vicinity of the Elkhorn Mountains and the Deer Creek volcanic fields in Montana. Seaward retreat of st randlines, marked by deposition of the Telegraph Creek, Eagle, Judith River, and Fox Hills Formations in Montana and the Mesaverde Formation in Wyoming, may be attributed to uplift in near-coastal areas and to an increase in volcaniclastic rocks delivered to the sea. Rates of transgression and regression determined for the Montana Group in central Montana reveal that the strandline movement was more rapid during times of transgression. The regression of the Telegraph Creek and Eagle strandlines averaged about 50 miles per million years compared with a rate of about 95 miles per million years for the advance of the strand-line during Claggett time. The Judith River regression averaged about 60 miles per million years compared with movement of the strandline during the Bearpaw advance of about 70 miles per million years. The final retreat of marine waters from Montana, marked by the Fox Hills regression, was about 35 miles per million years at first, but near the end of the regression it accelerated to a rate of about 500 miles per million years. Rates of sedimentation range from less than 50 feet per million years in the eastern parts of North and South Dakota to at least 2,500 feet in western Wyoming. The low rates in the Dakotas correspond well with modern rates in the open ocean, and the rates in western Wyoming approach the rate of present coastal sedimentation.

Montana, North Dakota, South Dakota, Wyoming↗
USGS2022

Nebraska and Landsat

The rolling plains of Nebraska occupy a storied place in the American psyche. For those living outside the Midwest, the Cornhusker State may be seen as a symbol of the Nation’s heartland, cropped border to border, with country churches and barely standing barns to be found around every turn of its gravel roads. Although the pioneer history and agricultural heritage of the 37th State lend credence to this idyllic view, Nebraska’s varied landscapes and modern economy make the reality of life in the State more complex than its rural image would suggest. Agriculture remains Nebraska’s top industry, but manufacturing now represents 12 percent of the State’s gross domestic product. The financial services and insurance industries account for 8 percent of the gross domestic product in Nebraska, which is the headquarters of Berkshire Hathaway and Mutual of Omaha, the latter of which is named after Nebraska’s largest city, which grew nearly 12 percent between 2010 and 2020. Cropland is indeed a prominent feature in Nebraska, but the State also is home to 8 State parks, 5 national parks, 2 national forests, and 3 national grasslands. The grasses and dunes of the Nebraska Sand Hills that stretch across the north-central quarter of the State are a National Natural Landmark. Data from the Landsat satellite program contribute to the study and management of Nebraska’s land in myriad ways, from monitoring crop productivity and aiding in rangeland management to tracking damage from floods, droughts, or hurricanes. Land cover maps produced using data pulled from the 50-year Landsat archive can offer important insights into urban growth, land use trends, and land change patterns. Here are a few examples of how Landsat has been used in Nebraska.

Nebraska↗
USGS2019

Variability in results from mineralogical and organic geochemical interlaboratory testing of U. S. Geological Survey shale reference materials

The expansion of unconventional petroleum resource exploration and production in the United States has led to an increase in source rock characterization efforts, particularly related to bulk organic and mineralogical properties. To support the analytical and research needs of industry and academia, as well as internal work, the U.S. Geological Survey (USGS) has collected and prepared shale geochemical reference materials (GRMs) from several major shale petroleum systems in the U.S. The sources of these materials are the Late Cretaceous Boquillas (lower Eagle Ford-equivalent) Formation (roadcut near Del Rio, TX), Late Cretaceous Mancos Shale (outcrop near Delta, CO), Devonian–Mississippian Woodford Shale (outcrop near Ardmore, OK), Late Cretaceous Niobrara Formation (quarry near Lyons, CO), Middle Devonian Marcellus Shale (creek bed in LeRoy, NY), and Eocene Mahogany zone oil shale of the Green River Formation (oil shale mine near Rifle, CO). Of particular interest in the development of these GRMs has been the examination of variability between laboratories and specific methods or instruments in commonly made measurements, including major- and trace-element concentrations, X-ray diffraction (XRD) mineralogy, total organic carbon (TOC) content, and programmed pyrolysis (PP) parameters. For the component concentrations and parameters we measured, the techniques and instrument types included: (1) elemental analysis by X-ray fluorescence, inductively coupled plasma mass spectrometry, and instrumental neutron activation analysis; (2) XRD mineralogy with various preparatory methods (spray drying or micronizing with or without internal standard); (3) TOC by combustion with infrared detection after carbonate removal or the PP approach; (4) PP by Rock-Eval 2 or more recently developed instruments (Rock-Eval 6, Source Rock Analyzer or SRA, and Hydrocarbon Analyzer With Kinetics or HAWK). Overall, the results showed that the selected shales cover a wide range of source rock organic and mineralogical properties. Major- and trace-element chemistry results showed low heterogeneity consistent with other USGS GRMs. Comparison of TOC results showed coefficients of variation (COV) of around 5% and the most consistent organic geochemical results between different laboratories and methods. Arguably the most relevant PP measurement, S2 or kerogen hydrocarbon-generating potential (mg-HC/g-rock), showed a somewhat wider range of variability than TOC (COV ~10%), but was consistent between the three modern instruments and the industry-standard Rock-Eval 2. Major phase mineralogy (mineral concentrations ≥10 wt. %, organic-free basis) were comparable between laboratories, but variability in minor phase identification and quantification was observed. Utilization of these shale GRMs as quality control samples and testing materials is expected to help support analytical and experimental efforts in the continued development of unconventional petroleum resources.

Colorado, Texas, Oklahoma↗
USGS1966

Evidence for an early recent warm interval in northwestern Alaska

A warm interval that began at least 10,000 years ago and lasted until at least 8300 years ago is recorded in the coastal tundra covered area of northwestern Alaska by the presence of fossil wood of tree size or tree species, fossil beaver-gnawed wood found beyond the modern range of beaver, evidence of ice-wedge melting, buried soils, and soils that extend below the top of modern permafrost. Dating of the warm interval is based on eight radiocarbon dates. Although these do not provide tight control for either the beginning or the end, they permit the interpretation that the warm event began at the start of the worldwide, postglacial warming and that it ended at the time of the Anivik Lake glacial readvance in the Brooks Range. If this is correct, the early Recent warm interval and the "postglacial thermal maximum" recognized by Livingstone in the Brooks Range were separated by a period of cooler climate. Deposits 7200 and 3600 years old also record moments when the climate was warmer than at present in coastal northwestern Alaska . Although these may record a continuation of the early Recent warm period, it seems more likely that they represent later and separate brief intervals of warmer climate. A postglacial thermal maximum between 6000 and 3000 years ago is recorded by pollen profiles in the Brooks Range, but is not clearly recorded in the coastal areas of northwestern Alaska . We suggest that as sea level rose to near its present position, the accompanying maritime climate lowered summer temperatures in this coastal area during the time at which areas farther inland were experiencing the high temperatures of the postglacial thermal maximum.

Alaska↗
USGS2007

Vertical gradients in water chemistry and age in the Northern High Plains Aquifer, Nebraska, 2003

The northern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of Colorado, Kansas, Nebraska, South Dakota, and Wyoming. Despite the aquifer’s importance to the regional economy, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey’s National Water-Quality Assessment Program, water samples from nested, short-screen monitoring wells installed in the northern High Plains aquifer were analyzed for major ions, nutrients, trace elements, dissolved organic carbon, pesticides, stable and radioactive isotopes, dissolved gases, and other parameters to evaluate vertical gradients in water chemistry and age in the aquifer. Chemical data and tritium and radiocarbon ages show that water in the aquifer was chemically and temporally stratified in the study area, with a relatively thin zone of recently recharged water (less than 50 years) near the water table overlying a thicker zone of older water (1,800 to 15,600 radiocarbon years). In areas where irrigated agriculture was an important land use, the recently recharged ground water was characterized by elevated concentrations of major ions and nitrate and the detection of pesticide compounds. Below the zone of agricultural influence, major-ion concentrations exhibited small increases with depth and distance along flow paths because of rock/water interactions. The concentration increases were accounted for primarily by dissolved calcium, sodium, bicarbonate, sulfate, and silica. In general, the chemistry of ground water throughout the aquifer was of high quality. None of the approximately 90 chemical constituents analyzed in each sample exceeded primary drinking-water standards. Mass-balance models indicate that changes in groundwater chemistry along flow paths in the aquifer can be accounted for by small amounts of feldspar and calcite dissolution; goethite and clay-mineral precipitation; organic-carbon and pyrite oxidation; oxygen reduction and denitrification; and cation exchange. Mixing with surface water affected the chemistry of ground water in alluvial sediments of the Platte River Valley. Radiocarbon ages in the aquifer, adjusted for carbon mass transfers, ranged from 1,800 to 15,600 14C years before present. These results have important implications with respect to development of ground-water resources in the Sand Hills. Most of the water in the aquifer predates modern anthropogenic activity so excessive removal of water by pumping is not likely to be replenished by natural recharge in a meaningful timeframe. Vertical gradients in ground-water age were used to estimate long-term average recharge rates in the aquifer. In most areas, the recharge rates ranged from 0.02 to 0.05 foot per year. The recharge rate was 0.2 foot per year in one part of the aquifer characterized by large downward hydraulic gradients. Nitrite plus nitrate concentrations at the water table were 0.13 to 3.13 milligrams per liter as nitrogen, and concentrations substantially decreased with depth in the aquifer. Dissolved-gas and nitrogen-isotope data indicate that denitrification in the aquifer removed 0 to 97 percent (average = 50 percent) of the nitrate originally present in recharge. The average amount of nitrate removed by denitrification in the aquifer north of the Platte River (Sand Hills) was substantially greater than the amount removed south of the river (66 as opposed to 0 percent), and the extent of nitrate removal appears to be related to the presence of thick deposits of sediment on top of the Ogallala Group in the Sand Hills that contained electron donors, such as organic carbon and pyrite, to support denitrification. Apparent rates of dissolved-oxygen reduction and denitrification were estimated on the basis of decreases in dissolved-oxygen concentrations and increases in concentrations of excess nitrogen gas and ground-water ages along flow paths from the water table to deeper wells. Median rates of dissolved-oxygen reduction and denitrification south of the Platte River were at least 10 times smaller than the median rates north of the river in the Sand Hills. The relatively large denitrification rates in the Sand Hills indicate that the aquifer in that area may have a greater capacity to attenuate nitrate contamination than the aquifer south of the river, depending on rates of ground-water movement in the two areas. Small denitrification rates south of the river indicate that nitrate contamination in that part of the aquifer would likely persist for a longer period of time.

Nebraska↗
USGS1992

The stable isotope geochemistry of acid sulfate alteration

Acid sulfate wall-rock alteration, characterized by the assemblage alunite + kaolinite + quartz + or - pyrite, results from base leaching by fluids concentrated in H 2 SO 4 . Requisite amounts of H 2 SO 4 can be generated by different mechanisms in three principal geologic environments: (1) by atmospheric oxidation of sulfides in the supergene environment, (2) by atmospheric oxidation at the water table in the steam-heated environment of H 2 S released by deeper, boiling fluids, and (3) by the disproportionation of magmatic SO 2 to H 2 S and H 2 SO 4 during condensation of a magmatic vapor plume at intermediate depths in magmatic hydrothermal environments in silicic and andesitic volcanic terranes. In addition, coarse vein alunite may form in a magmatic steam environment from rapid release of an SO 2 -rich magmatic vapor phase at high temperature and low pressure or from the oxidation of a more reduced magmatic vapor by entrained atmospheric oxygen in the carapace of a volcanic edifice.Alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] contains four stable isotope sites and complete analyses (delta D, delta 18 O (sub SO 4 ) , delta 18 O OH , and delta 34 S) are now possible. Except for delta 18 O OH in magmatic hydrothermal alunites, primary values are usually retained. In cooperation with many colleagues, over 500 measurements have been made on nearly 200 samples of alunite and associated minerals from 23 localities, and 55 additional analyses have been taken from the literature. This survey confirms that kinetic factors play an important role in the stable isotope systematics of alunite and acid sulfate alteration. To a very large extent they form the isotopic basis for distinguishing between environments of acid sulfate alteration, and they provide important insights into attendant processes. Stable isotope analyses of alunite, often in combination with those on associated sulfides and kaolinite, permit recognition of environments of formation and provide information on origins of components, processes (including rates), physical-chemical environments, and temperatures of formation.Supergene acid sulfate alteration may form over any sulfide zone when it is raised above the water table by tectonics or exposed by erosion. It may overprint earlier acid sulfate assemblages, particularly the magmatic hydrothermal assemblages which are pyrite rich such as at El Salvador, Chile; Rodalquilar, Spain; and Goldfield, Nevada. Supergene alunite normally has delta 34 S values virtually identical to precursor sulfides unless bacteriogenic reduction of aqueous sulfate takes place in standing pools of water. delta D values are close to that of local meteoric water unless extensive evaporation occurs. delta D and delta 18 O OH values of supergene alunites from a range of latitudes fall in a broad zone parallel to the meteoric water line much the way delta D and delta 18 O values of associated halloysite-kaolinite fall near the kaolinite line of Savin and Epstein (1970). delta 18 O (sub SO 4 ) values are kinetically controlled and will reflect the hydro-geochemistry of the environment. delta 18 O (sub SO 4 -OH) alues are grossly out of equilibrium and large negative values are definitive of a supergene origin.In steam-heated environments, such as those at the Tolfa district, Italy, and Marysvale, Utah, and numerous modern geothermal systems, acid sulfate alteration zones are characterized by pronounced vertical zoning. Such acid sulfate alteration may occur over adularia-sericite-type base and precious metal ore deposits such as the one at Buckskin, Nevada. Initial delta 18 O (sub SO 4 ) and delta 34 S values are kinetically controlled, but delta 18 O (sub SO 4 ) values usually reach equilibrium with fluids, and even delta 34 S values may reflect partial exchange with H 2 S where the residence time of aqueous sulfate is sufficient. Most alunites of steam-heated origin have delta 34 S values the same as those of precursor H 2 S (and as related sulfides, if present) and delta D values similar to that of local meteoric water. In the samples analyzed, most delta 18 O (sub SO 4 -OH) values give reasonable temperatures of 90 degrees to 160 degrees C, indicating that delta 18 O (sub SO 4 ) and delta 18 O OH values reflect a close approach to equilibrium with the fluid. The delta 18 O (sub SO 4 ) and delta 18 O OH values also reflect the degree of exchange of the meteoric fluids with wall rock. Coeval kaolinites typically have delta 18 O and delta D values to the left of the kaolinitc line.Magmatic hydrothermal, acid sulfate alteration zones in near-surface epithermal deposits such as Summitville, Colorado. Julcani, Peru, and Red Mountain and Lake City, Colorado, are characterized by vertical orientation and horizontal zoning, the presence of coeval pyrite, PO 4 analogues of alunite, zunyite, and later gold, pyrite and enargite, and often other Cu-As-Sb-S minerals. Acid sulfate alteration assemblages also occur as late stages in the porphyry-copper deposit at E1 Salvador, Chile. In the examples studied, magmatic hydrothermal alunites have delta D values close to those for magmatic water. delta 34 S values are 16 to 28 per mil larger than those for associated pyrite, reflecting equilibrium between aqueous H 2 S and SO 4 formed by the disproportionation of magmatically derived SO 2 . delta 18 O (sub SO 4 ) values are usually 8 to 18 per mil and vary systematically with delta 34 S values, reflecting variations in temperature and/or H 2 S/SO 4 fluid ratios. Further variation in delta 18 O (sub SO 4 ) values may result if SO 2 condenses in mixed magmatic meteoric water fluids. delta 18 O (sub SO (sub 4-) OH) values of magmatic hydrothermal alunites are generally unsuitable for temperature determinations because of retrograde exchange in the OH site, but delta 34 S (sub alunite-pyrite) values provide reliable temperature estimates.Magmatic steam environments appear to occur over a range of depths and are characterized by monomineralic veins of coarse alunite in variably alunitized and kaolinized wall rocks containing minor pyrite. Alunite formed in the magmatic steam environment can usually be recognized by delta 34 S near delta 34 S (sub Sigma S) values and delta D and delta 18 O (sub SO 4 ) values near magmatic values. Magmatic steam alunite differs from magmatic hydrothermal alunite by having delta 34 S close to delta 34 S (sub Sigma S) values of the system. delta 18 O (sub SO (sub 4-) OH) values of most magmatic steam alunite give temperatures ranging from 90 degrees to 210 degrees C but, for reasons which are not understood, some temperatures as well as calculated delta 18 O (sub H 2 O) values are too low for presumed precipitation from a magmatic vapor phase. Magmatic steam environments may occur over porphyry-type mineralization as at Red Mountain, Colorado, and Alunite Ridge, Utah, and over or adjacent to adularia-sericite-type deposits in volcanic domes as at Cactus, California.

Economic Geology↗
USGS1964

Availability of ground water in parts of the Acoma and Laguna Indian Reservations, New Mexico

The need for additional water has increased in recent years on the Acoma and Laguna Indian Reservations in west-central New Mexico because the population and per capita use of water have increased; the tribes also desire water for light industry, for more modern schools, and to increase their irrigation program. Many wells have been drilled in the area, but most have been disappointing because of small yields and poor chemical quality of the water. The topography in the Acoma and Laguna Indian Reservations is controlled primarily by the regional and local dip of alternating beds of sandstone and shale and by the igneous complex of Mount Taylor. The entrenched alluvial valley along the Rio San Jose, which traverses the area, ranges in width from about 0.4 mile to about 2 miles. The climate is characterized by scant rainfall, which occurs mainly in summer, low relative humidity, and large daily fluctuations of temperature. Most of the surface water enters the area through the Rio San Jose. The average annual streamflow past the gaging station Rio San Jose near Grants, N. Mex. is about 4,000 acre-feet. Tributaries to the Rio San Jose within the area probably contribute about 1,000 acre-feet per year. At the present time, most of the surface water is used for irrigation. Ground water is obtained from consolidated sedimentary rocks that range in age from Triassic to Cretaceous, and from unconsolidated alluvium of Quaternary age. The principal aquifers are the Dakota Sandstone, the Tres Hermanos Sandstone Member of the Mancos Shale, and the alluvium. The Dakota Sandstone yields 5 to 50 gpm (gallons per minute) of water to domestic and stock wells. The Tres Hermanos sandstone Member generally yields 5 to 20 gpm of water to domestic and stock wells. Locally, beds of sandstone in the Chinle and Morrison Formations, the Entrada Sandstone, and the Bluff Sandstone also yield small supplies of water to domestic and stock wells. The alluvium yields from 2 gpm to as much as 150 gpm of water to domestic and stock wells. Thirteen test wells were drilled in a search for usable supplies of ground water for pueblo and irrigation supply and to determine the geologic and hydrologic characteristics of the water-bearing material. The performance of six of the test wells suggests that the sites are favorable for pueblo or irrigation supply wells. The yield of the other seven wells was too small or the quality of the water was too poor for development of pueblo or irrigation supply to be feasible. However, the water from one of the seven wells was good in chemical quality, and the yield was large enough to supply a few homes with water. The tests suggest that the water in the alluvium of the Rio San Jose valley is closely related to the streamflow and that it might be possible to withdraw from the alluvium in summer and replenish it in winter. The surface flow in summer might be decreased by extensive pumpage of ground water, but on the other hand, more of the winter flow could be retained in the area by storage in the ground-water reservoir. Wells could be drilled along the axis of the valley, and the water could be pumped into systems for distribution to irrigated farms. The chemical quality of ground water in the area varies widely from one stratigraphic unit to another and laterally within each unit and commonly the water contains undesirably large amounts of sulfate. However, potable water has been obtained locally from all the aquifers. The water of best quality seemingly is in the Tres Hermanos Sandstone Member of the Mancos Shale and in the alluvium north of the Rio San Jose. The largest quantity of water that is suitable for irrigation is in the valley fill along the Rio San Jose. Intensive pumping of ground water from aquifers containing water of good quality may draw water of inferior chemical quality into the wells.

Water Supply Paper↗
USGS2013

Anatomy of La Jolla submarine canyon system; offshore southern California

An autonomous underwater vehicle (AUV) carrying a multibeam sonar and a chirp profiler was used to map sections of the seafloor within the La Jolla Canyon, offshore southern California, at sub-meter scales. Close-up observations and sampling were conducted during remotely operated vehicle (ROV) dives. Minisparker seismic-reflection profiles from a surface ship help to define the overall geometry of the La Jolla Canyon especially with respect to the pre-canyon host sediments. The floor of the axial channel is covered with unconsolidated sand similar to the sand on the shelf near the canyon head, lacks outcrops of the pre-canyon host strata, has an almost constant slope of 1.0° and is covered with trains of crescent shaped bedforms. The presence of modern plant material entombed within these sands confirms that the axial channel is presently active. The sand on the canyon floor liquefied during vibracore collection and flowed downslope, illustrating that the sediment filling the channel can easily fail even on this gentle slope. Data from the canyon walls help constrain the age of the canyon and extent of incision. Horizontal beds of moderately cohesive fine-grained sediments exposed on the steep canyon walls are consistently less than 1.232 million years old. The lateral continuity of seismic reflectors in minisparker profiles indicate that pre-canyon host strata extend uninterrupted from outside the canyon underneath some terraces within the canyon. Evidence of abandoned channels and point bar-like deposits are noticeably absent on the inside bend of channel meanders and in the subsurface of the terraces. While vibracores from the surface of terraces contain thin (< 10 cm) turbidites, they are inferred to be part of a veneer of recent sediment covering pre-canyon host sediments that underpin the terraces. The combined use of state of the art seafloor mapping and exploration tools provides a uniquely detailed view of the morphology within an active submarine canyon.

California↗