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USGS2022

Magmatism, migrating topography, and the transition from Sevier shortening to Basin and Range extension, western United States

The paleogeographic evolution of the western U.S. Great Basin from the Late Cretaceous to the Cenozoic is critical to understanding how the North American Cordillera at this latitude transitioned from Mesozoic shortening to Cenozoic extension. According to a widely applied model, Cenozoic extension was driven by collapse of elevated crust supported by crustal thicknesses that were potentially double the present ~30–35 km. This model is difficult to reconcile with more recent estimates of moderate regional extension (≤50%) and the discovery that most high-angle, Basin and Range faults slipped rapidly ca. 17 Ma, tens of millions of years after crustal thickening occurred. Here, we integrated new and existing geochronology and geologic mapping in the Elko area of northeast Nevada, one of the few places in the Great Basin with substantial exposures of Paleogene strata. We improved the age control for strata that have been targeted for studies of regional paleoelevation and paleoclimate across this critical time span. In addition, a regional compilation of the ages of material within a network of middle Cenozoic paleodrainages that developed across the Great Basin shows that the age of basal paleovalley fill decreases southward roughly synchronous with voluminous ignimbrite flareup volcanism that swept south across the region ca. 45–20 Ma. Integrating these data sets with the regional record of faulting, sedimentation, erosion, and magmatism, we suggest that volcanism was accompanied by an elevation increase that disrupted drainage systems and shifted the continental divide east into central Nevada from its Late Cretaceous location along the Sierra Nevada arc. The north-south Eocene–Oligocene drainage divide defined by mapping of paleovalleys may thus have evolved as a dynamic feature that propagated southward with magmatism. Despite some local faulting, the northern Great Basin became a vast, elevated volcanic tableland that persisted until dissection by Basin and Range faulting that began ca. 21–17 Ma. Based on this more detailed geologic framework, it is unlikely that Basin and Range extension was driven by Cretaceous crustal overthickening; rather, preexisting crustal structure was just one of several factors that that led to Basin and Range faulting after ca. 17 Ma—in addition to thermal weakening of the crust associated with Cenozoic magmatism, thermally supported elevation, and changing boundary conditions. Because these causal factors evolved long after crustal thickening ended, during final removal and fragmentation of the shallowly subducting Farallon slab, they are compatible with normal-thickness (~45–50 km) crust beneath the Great Basin prior to extension and do not require development of a strongly elevated, Altiplano-like region during Mesozoic shortening.

Nevada↗

USGS2018

The Las Vegas Formation

The Las Vegas Formation was established in 1965 to designate the distinctive light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada. In a coeval designation, the sediments were subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the literature. Use of the Las Vegas Formation name over the past half century has been hampered because of the lack of a robust definition and characterization of the entire lithostratigraphic sequence, its geographic distribution, and chronology. This study evaluates and describes deposits attributed to the Las Vegas Formation with detailed stratigraphy, sedimentology, and field relations. A large suite of radiocarbon and luminescence ages facilitates revision and temporal expansion of the geochronology. In all, we characterize 17 informal geologic units within the formation, each dating to a unique period of geologic time, with stratigraphically ascending members X, A, B, D, and E and attendant beds in members B, D, and E. The age of the Las Vegas Formation spans at least the middle Pleistocene to early Holocene (from approximately 573 to 8.53 kilo-annum [thousands of years before present]) and is related to past episodes of groundwater discharge in the Las Vegas Valley. The contextual information derived from this new framework is dually noteworthy because the sediments entomb one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represent a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Characterizing the nature of these important deposits stabilizes the nomenclature, promotes the continued use of the informal units within the formation, and facilitates studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern United States.

Nevada↗

USGS2014

Discussion of “tide‐producing forces and artesian pressures”

I was an employee of the Texas State Board of Water Engineers in charge of the Fort Stockton field office at the time that the data for this paper were gathered. Since I have done both extensive and detailed ground‐water work in the Fort Stockton area, including the setting and maintaining of the water‐stage recorder at the Gonzales well, I believe I can add some pertinent hydrologic remarks about this paper. The authors state that the principal water‐bearing formation is a limestone. This opinion is not shared by myself and most likely the majority of other geologists in this area. Adkins [1927] favored the basal Cretaceous sands as the principal source of water to Comanche Springs. I believe that the most extensive and the principal water‐bearing formation is a sand and sandstone. The crevices and channels reported in wells and exposed at the springs are only a localized condition resulting from structural weakness and solution caused by a high water surface. The piezometric surface in sand and crevice wells is essentially identical; this suggests that there exists but one principal aquifer in this area. W.N. White, former District Geologist in Texas for the U.S. Geological Survey, in a personal communication to me in 1948, reported Comanche Springs to be the most reliable springs in Texas. This reliable flow strongly supports the concept of a sand aquifer, whose catchment area, or source, is of vast and varied extent, and a great distance from its outlet.

Eos, Transactions, American Geophysical Union↗

USGS1992

Age and nature of the basement in northeastern Washington and northern Idaho: isotopic evidence from Mesozoic and Cenozoic granitoids

K-feldspar Pb and whole rock Nd isotopic analyses from 25 Mesozoic and Cenozoic plutonic rocks and two gneisses from NE Washington and northern Idaho are used to elucidate the age and nature of the concealed cratonic basement. The plutons form two highly distinct isotopie groups: Group I (hornblende-biotite and two-mica plutons of all ages) have Pb isotopie compositions suggesting derivation from rocks of the Belt Supergroup or their metamorphosed equivalents, although Nd isotopie data can only support this model if there was a significant input of juvenile mantle-derived or ancient light REE-depleted material. Group II (hornblende-biotite of Eocene age) have highly retarded Pb isotopie compositions relative to the present day crustal average and require a source region with long-term U (and other LIL) depletion, characteristic of cratonic lower crust. A U-Pb zircon upper intercept age of ca. 2600 Ma obtained from one of the Group II samples, together with Sm-Nd data from the gneisses, indicates possible late-Archean crust at depth, which acted as a source region for Eocene extension-related plutonism. Isotopie compositions and apparent geochemical evolution do not support a direct correlation with the nearest exposed North American Craton in the Wyoming province. If it represents attenuated pre-Mesozoic craton, then it must have been accreted to the craton prior to development of the miogeocline in the Late Proterozoic. Alternatively, it may be part of the Cordilleria terrane accreted to the craton in the Early Cretaceous.

Journal of Geology↗

USGS1997

Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

California↗

USGS2007

Increasing resiliency to natural hazards - A strategic plan for the Multi-Hazards Demonstration Project in Southern California

The U.S. Geological Survey (USGS) is initiating a new project designed to improve resiliency to natural hazards in southern California through the application of science to community decision making and emergency response. The Multi-Hazards Demonstration Project will assist the region’s communities to reduce their risk from natural hazards by directing new and existing research towards the community’s needs, improving monitoring technology, producing innovative products, and improving dissemination of the results. The natural hazards to be investigated in this project include coastal erosion, earthquakes, floods, landslides, tsunamis, and wildfires. Americans are more at risk from natural hazards now than at any other time in our Nation’s history. Southern California, in particular, has one of the Nation’s highest potentials for extreme catastrophic losses due to natural hazards, with estimates of expected losses exceeding $3 billion per year. These losses can only be reduced through the decisions of the southern California community itself. To be effective, these decisions must be guided by the best information about hazards, risk, and the cost-effectiveness of mitigation technologies. The USGS will work with collaborators to set the direction of the research and to create multi-hazard risk frameworks where communities can apply the results of scientific research to their decision-making processes. Partners include state, county, city, and public-lands government agencies, public and private utilities, companies with a significant impact and presence in southern California, academic researchers, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), and local emergency response agencies. Prior to the writing of this strategic plan document, three strategic planning workshops were held in February and March 2006 at the USGS office in Pasadena to explore potential relationships. The goal of these planning sessions was to determine the external organizations’ needs for mitigation efforts before potential natural hazard events, and response efforts during and after the event. On the basis of input from workshop participants, four priority areas were identified for future research to address. They are (1) helping decision makers design planning scenarios, (2) improving upon the mapping of multiple hazards in urban areas, (3) providing real-time information from monitoring networks, and (4) integrating information in a risk and decision-making analysis. Towards this end, short-term and out-year goals have been outlined with the priorities in mind. First-year goals are (1) to engage the user community to establish the structures and processes for communications and interactions, (2) to develop a program to create scenarios of anticipated disasters, beginning in the first year with a scenario of a southern San Andreas earthquake that triggers secondary hazards, (3) to compile existing datasets of geospatial data, and (4) to target research efforts to support more complete and robust products in future years. Both the first-year and out-year goals have been formulated around a working-group structure that builds on existing research strengths within the USGS. The project is intended to demonstrate how developments in methodology and products can lead to improvement in our management of natural hazards in an urban environment for application across the Nation.

Open-File Report↗

USGS2017

Hydrology of the Claiborne aquifer and interconnection with the Upper Floridan aquifer in southwest Georgia

The U.S. Geological Survey conducted a study, in cooperation with the Georgia Environmental Protection Division, to define the hydrologic properties of the Claiborne aquifer and evaluate its connection with the Upper Floridan aquifer in southwest Georgia. The effort involved collecting and compiling hydrologic data from the aquifer in subarea 4 of southwestern Georgia. Data collected for this study include borehole geophysical logs in 7 wells, and two 72-hour aquifer tests to determine aquifer properties. The top of the Claiborne aquifer extends from an altitude of about 200 feet above the North American Vertical Datum of 1988 (NAVD 88) in Terrell County to 402 feet below NAVD 88 in Decatur County, Georgia. The base of the aquifer extends from an altitude of about 60 feet above NAVD 88 in eastern Sumter County to about 750 feet below NAVD 88 in Decatur County. Aquifer thickness ranges from about 70 feet in eastern Early County to 400 feet in Decatur County. The transmissivity of the Claiborne aquifer, determined from two 72-hour aquifer tests, was estimated to be 1,500 and 700 feet squared per day in Mitchell and Early Counties, respectively. The storage coefficient was estimated to be 0.0006 and 0.0004 for the same sites, respectively. Aquifer test data from Mitchell County indicate a small amount of leakage occurred during the test. Groundwater-flow models suggest that the source of the leakage was the underlying Clayton aquifer, which produced about 2.5 feet of drawdown in response to pumping in the Claiborne aquifer. The vertical hydraulic conductivity of the confining unit between the Claiborne and Clayton aquifers was simulated to be about 0.02 foot per day. Results from the 72-hour aquifer tests run for this study indicated no interconnection between the Claiborne and overlying Upper Floridan aquifers at the two test sites. Additional data are needed to monitor the effects that increased withdrawals from the Claiborne aquifer may have on future water resources.

Georgia↗

USGS2011

The Sculptured Hills of the Taurus Highlands: Implications for the relative age of Serenitatis, basin chronologies and the cratering history of the Moon

New images from the Lunar Reconnaissance Orbiter Camera show the distribution and geological relations of the Sculptured Hills, a geological unit widespread in the highlands between the Serenitatis and Crisium basins. The Sculptured Hills shows knobby, undulating, radially textured, and plains-like morphologies and in many places is indistinguishable from the similarly knobby Alpes Formation, a facies of ejecta from the Imbrium basin. The new LROC image data show that the Sculptured Hills in the Taurus highlands is Imbrium ejecta and not directly related to the formation of the Serenitatis basin. This occurrence and the geological relations of this unit suggests that the Apollo 17 impact melts may not be not samples of the Serenitatis basin-forming impact, leaving their provenance undetermined and origin unexplained. If the Apollo 17 melt rocks are Serenitatis impact melt, up to half of the basin and large crater population of the Moon was created within a 30 Ma interval around 3.8 Ga in a global impact "cataclysm." Either interpretation significantly changes our view of the impact process and history of the Earth-Moon system. Copyright 2011 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2013

The United States-Mexican Border - A land of conflict and opportunity: Chapter 1 in United States-Mexican Borderlands: Facing tomorrow's challenges through USGS science

The boundary between the United States and Mexico was created for convenient expediency through political debate and agreements (fig. 1–1). With the exception of the eastern segment of the border, which follows the course of the Rio Grande (known as the Rio Bravo in Mexico), the defining of this border was based on political decisions that had little concern for ecosystems, geologic features, or water—all of which span that imaginary line. However, the location of the border has had a remarkable effect on the biologic and physical systems in the border region and, in turn, has had a growing influence on what we now see as 21st century socioeconomic and environmental priorities. Because of the complex interactions of the human, ecological, political, and economic exigencies associated with this area, the status of the United States–Mexican border region, known as the Borderlands, has become an ever-present concern for most American citizens and for Mexican and United States Federal, State, and local governments.

United States-Mexico Borderlands↗

USGS2008

Sandy signs of a tsunami's onshore depth and speed

Tsunamis rank among the most devastating and unpredictable natural hazards to affect coastal areas. Just 3 years ago, in December 2004, the Indian Ocean tsunami caused more than 225,000 deaths. Like many extreme events, however, destructive tsunamis strike rarely enough that written records span too little time to quantify tsunami hazard and risk. Tsunami deposits preserved in the geologic record have been used to extend the record of tsunami occurrence but not the magnitude of past events. To quantify tsunami hazard further, we asked the following question: Can ancient deposits also provide guidance on the expectable water depths and speeds for future tsunamis?

Eos, Transactions, American Geophysical Union↗

USGS2014

Investigations of the fluctuations of water‐levels in observation‐wells in Virginia

An automatic water ‐stage recorder has been maintained on an observation ‐ well in Arlington County, Virginia , about 1‐½ miles from the United States Weather Bureau, in Washington, D.C., since June, 1928, but there are a few interruptions in the record. This is a dug well , about 28 feet deep and extends through terrace deposits of gravelly silt or loam. It has not been used for water ‐supply during the period of record. The recorder was installed by the United States Geological Survey and the record has been given considerable study by O. E. Meinzer, W. N. White, and L. K. Wensel, all of the Geological Survey. In July, 1931, the study of this well was made a part of a more comprehensive investigation of the ground‐ water resources of Virginia in cooperation with the State Geological Survey, which was assigned to the writer. The well is essentially of the water ‐table type, and its hydrograph shows approximately the periods of rainfall‐penetration and the relative amounts of recharge in each of these periods. The record is especially instructive because of certain unusual climatic conditions that have existed in the last four years.

Virginia↗

USGS1990

Stratigraphy and tectonics of Paleozoic arc-related rocks of the northernmost Sierra Nevada, California; The eastern Klamath and northern Sierra terranes

The Eastern Klamath and Northern Sierra terranes of northern California consist of Devonian to Jurassic arc-related rocks that structurally and/or stratigraphically overlie Devonian(?) or older complexes that consist of quartzite, quartzofeldspathic sandstone, chert, and mafic and ultramafic rocks. These terranes lie within a regional belt of Paleozoic arc-related rocks that can be recognized from the Sierra Nevada to British Columbia. The Eastern Klamath and Northern Sierra terranes are geographically separate and have paleontologic linkage, but lack direct stratigraphic ties in strata of Late Devonian to Early Permian age. This chapter describes new stratigraphic correlations and structural interpretations of rocks that lie in the northernmost part of the Sierra Nevada. These rocks include the Butt Valley block of the Northern Sierra terrane, and rocks herein interpreted as dismembered Eastern Klamath terrane. The rocks of Eastern Klamath terrane affinity, Soda Ravine block, occur as a tectonic sliver that lies to the west of the Butt Valley block. The Soda Ravine block is about 2 to 4 km by 20 km and includes limestone lenses equivalent to zone A of the McCloud Limestone of the Eastern Klamath terrane, and upper Middle and Upper Triassic limestone, slate, siltstone, and pebble conglomerate. Similar Permian limestone with McCloud faunal affinities and slate-bearing slivers have been noted by previous workers in this area and to the south. The Butt Valley block had previously been interpreted as part of the west limb of a regional anticline, the Almanor anticline. New mapping suggests that the block is not contiguous with rocks that lie to the east. The Butt Valley block includes the Devonian and Mississippian Taylor Formation, which is unconformably overlain by an Upper Triassic (Carnian and Norian) basal conglomerate and sandstone, which in turn is overlain by Upper Triassic limestone. The Upper Triassic limestone is overlain by a sparsely fossiliferous, lithic-volcaniclastic sequence containing poorly preserved Triassic or Early Jurassic, and probable Early Jurassic, ammonites and clams. This sequence is similar to conglomerate, Triassic limestone, and volcaniclastic rocks of the Jurassic Sailor Canyon Formation, which overlie a regional Late Triassic unconformity west of Lake Tahoe, thus expanding the known distribution of the unconformity in the Sierra Nevada. The Triassic unconformity overlies Carboniferous and older rocks around the North Fork American River area to the south, and overlies Devonian and older rocks on the Butt Valley block, but overlies Permian rocks east and southeast of the Butt Valley block. These relations suggest that either the Butt Valley block was part of a highland or uplifted block along the western part of the northern Sierra terrane or that the Butt Valley block previously lay closer to the North Fork American River area and has been translated northward by right-slip displacement. Northern Sierra terrane east of the Butt Valley block consists of the Hough and Genesse blocks, which are separated by the Grizzly Mountain fault zone. The Grizzly Mountain fault zone is here interpreted to be a transpressional right-slip fault.

California↗

USGS2004

Landsat yesterday and today: An American vision and an old challenge

Since the late 1960s, the United States government has invested more than $1 billion in designing, launching, and operating the Landsat (land satellite) series of Earth-observing satellites. Global change researchers, geologists, and environmental scientists have used images gathered by the satellites for purposes ranging from human health research, energy exploration, and pollution detection to agricultural assessments, urban growth monitoring, and earthquake lineament studies. The earliest data were captured on a digital medium called wide-band video tape (WBVT). However, two decades of unsound media storage conditions and a poorly maintained processing system have left the physically deteriorating WBVTs with no mechanism for interpretation. A national treasure was in jeopardy. With seed money from the National Aeronautics and Space Administration (NASA), the U.S. Geological Survey (USGS) began a project to rescue the data. More than 21,000 tapes from the 1970s have been transcribed to stable, archival media, preserving the data for future studies in Earth System Science.

Journal of Map & Geography Libraries↗

USGS2002

Geology of St. John, U.S. Virgin Islands

The rocks of St. John, which is located near the eastern end of the Greater Antilles and near the northeastern corner of the Caribbean plate, consist of Cretaceous basalt, andesite, keratophyre, their volcaniclastic and hypabyssal intrusive equivalents, and minor calcareous rocks and chert. These rocks were intruded by Tertiary mafic dikes and tonalitic plutons. The oldest rocks formed in an extensional oceanic environment characterized by abundant keratophyre and sheeted dikes. Subduction-related volcanism of the east-west-trending marine Greater Antilles volcanic arc began on St. John near the transition between the Early and Late Cretaceous. South-directed compression, probably caused by the initial collision between the Greater Antilles arc of the Caribbean plate and the Bahama platform of the North American plate, deformed the Cretaceous strata into east-west-trending folds with axial-plane cleavage. Late Eocene tonalitic intrusions, part of the Greater Antilles arc magmatism, produced a contact aureole that is as much as two kilometers wide and that partly annealed the axial-plane cleavage. East-west compression, possibly related to the relative eastward transport of the Caribbean plate in response to the beginning of spreading at the Cayman Trough, produced long-wavelength, low-amplitude folds whose axes plunge gently north and warp the earlier folds. A broad north-plunging syncline-anticline pair occupies most of St. John. The last tectonic event affecting St. John is recorded by a series of post-late Eocene sinistral strike-slip faults related to the early stages of spreading at the Cayman Trough spreading center and sinistral strike-slip accommodation near the northern border of the Caribbean plate. Central St. John is occupied by a rhomb horst bounded by two of these sinistral faults. Unlike other parts of the Greater Antilles, evidence for recent tectonic movement has not been observed on St. John.

Professional Paper↗

USGS2019

Applying the Community Ice Sheet Model to evaluate PMIP3 LGM climatologies over the North American ice sheets

We apply the Community Ice Sheet Model (CISM2) to determine the extent to which the Last Glacial Maximum (LGM) temperature and precipitation climatologies from the Paleoclimate Modelling Intercomparison Project 3 (PMIP3) simulations support the large North American ice sheets that were prescribed as a boundary condition. We force CISM2 with eight PMIP3 general circulation models (GCMs), and an additional model, GENMOM. Seven GCMs simulate LGM climatologies that support positive surface mass balances of the Laurentide and Cordilleran ice sheets (LIS, CIS) consistent with where ice was prescribed in the GCMs. Two GCMs simulate July temperatures that are too warm to support the ice sheets. Four of the nine CISM2 simulations support ice sheets in Beringia, in absence of prescribed ice in the driving GCMs and in disagreement with geologic evidence that indicates the area remained ice-free during the LGM. We test the sensitivity of our results to a range of snow and ice positive degree-day factors, daily, monthly, and climatological temperature and precipitation inputs, and we evaluate the role of albedo and snow in the simulations. Areas with perennial snow in the GCM simulations correspond well to the presence of ice in the CISM2 simulation. GCMs with unrealistically low surface albedos over the LIS yield simulations that fail to simulate realistic ice sheets.

Climate Dynamics↗

USGS2005

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

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

Sonora↗

USGS2005

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

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

Texas↗

USGS2014

The measurement and computation of flood‐discharge

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

Eos, Transactions, American Geophysical Union↗