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At least 631 records · Page 35Linked to original sources
USGS2022

Field-trip guide to continental arc to rift volcanism of the southern Rocky Mountains—Southern Rocky Mountain, Taos Plateau, and Jemez Mountains volcanic fields of southern Colorado and northern New Mexico

The southern Rocky Mountains of northern New Mexico and southern Colorado preserve the Oligocene to Pleistocene record of North American continental arc to rift volcanism. The 35–23 million year old (Ma) southern Rocky Mountain volcanic field (SRMVF), spectacularly preserved in the San Juan Mountains of southern Colorado, records the evolution of large andesitic stratovolcanoes to complex caldera clusters, from which at least 22 major ignimbrite sheets (each 150–5,000 cubic kilometers) were erupted. Outflow deposits of the SRMVF preserved along the broadly uplifted northwest flank of the northern Rio Grande rift basin (the San Luis Valley) provide critical structural and temporal constraints on the inception of crustal extension. Coincident with waning stages of SRMVF caldera-forming volcanism (~25.4 Ma), extensional tectonism was accompanied by a transition from bimodal early Miocene to intermediate-composition late Miocene and dominantly basaltic Pliocene rift volcanism of the Taos Plateau in the southern San Luis Basin. Concomitant rift volcanism in the Española Basin and bordering Jemez Mountains of northern New Mexico records a similar Miocene eruptive history dominated by intermediate-composition volcanism that transitioned locally to Pliocene rift-related basaltic volcanism of the Cerros del Rio volcanic field and culminated in eruptions of the iconic rhyolitic Pleistocene Bandelier Tuff and formation of the Valles Caldera along the northwestern rift-basin margin. This 6-day, 7-night field trip will focus, in broadly equal proportions, on rift-related extensional volcanism of the Jemez Mountains and Taos Plateau regions during the first half of the trip, and on caldera-forming volcanism of the southern Rocky Mountain volcanic field during the second half of the trip. The 35-million-year volcanic history of the region highlighted by new geologic mapping, high-resolution geochronology, petrologic, geochemical, and geophysical data facilitates discussion of (1) the magmatic response to the tectonic transition from subducted-slab arc to continental-rift volcanism; (2) the nature and temporal evolution of rift magmas; (3) fault controls on the spatial evolution of rift magmatism; (4) the diversity of continental-arc ignimbrite volcanism and associated lavas; (5) ignimbrite caldera structure and associated intrusions in three-dimension; (6) the role of recycled crystal mush and magmatic cumulates during growth of Cordilleran batholiths; and (7) high-precision geochronologic contributions to interpretation of relations between regional tectonic and volcanic processes. Most stops will be along roads, but there will be moderate hikes on trails of less than 1-hour duration covering 1–2 kilometers (0.6–1.2 miles) with modest elevation gain of <150 meters (<492 feet). The route will progress in reverse stratigraphic order, starting in the Jemez Mountains of New Mexico and proceed northward to San Luis Basin and San Luis Hills before turning west to the southeast and central San Juan Mountains. Our last full day takes us to the little-visited and only recently mapped, Bonanza caldera of the northeastern San Juan Mountains and on the final day, we leave the San Luis Valley to briefly explore the Tertiary subvolcanic plutons of the Collegiate Range along the west side of the Arkansas Valley rift valley, en route to Denver. The authors of all daily contributions acknowledge the helpful reviews by Amy Gilmer and Joe Colgan and thank Christine Chan and Jeremy Havens for assistance with figures, tables, and guidebook text.

Colorado, New Mexico↗
USGS2001

Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado

New 1:24,000-scale geologic mapping in the Colorado National Monument Quadrangle and adjacent areas, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of and data for the stratigraphy, structure, geologic hazards in the area from the Colorado River in Grand Valley onto the Uncompahgre Plateau. The plateau drops abruptly along northwest-trending structures toward the northeast 800 m to the Redlands area and the Colorado River in Grand Valley. In addition to common alluvial and colluvial deposits, surficial deposits include Holocene and late Pleistocene charcoal-bearing valley-fill deposits, late to middle Pleistocene river-gravel terrace deposits, Holocene to middle Pleistocene younger, intermediate, and old fan-alluvium deposits, late to middle Pleistocene local gravel deposits, Holocene to late Pleistocene rock-fall deposits, Holocene to middle Pleistocene young and old landslide deposits, Holocene to late Pleistocene sheetwash deposits and eolian deposits, and Holocene Cienga-type deposits. Only the lowest part of the Upper Cretaceous Mancos Shale is exposed in the map area near the Colorado River. The Upper and Lower? Cretaceous Dakota Formation and the Lower Cretaceous Burro Canyon Formation form resistant dipslopes in the Grand Valley and a prominent ridge on the plateau. Less resistant strata of the Upper Jurassic Morrison Formation consisting of the Brushy Basin, Salt Wash, and Tidwell Members form slopes on the plateau and low areas below the mountain front of the plateau. The Middle Jurassic Wanakah Formation nomenclature replaces the previously used Summerville Formation. Because an upper part of the Middle Jurassic Entrada Formation is not obviously correlated with strata found elsewhere, it is therefore not formally named; however, the lower rounded cliff former Slickrock Member is clearly present. The Lower Jurassic silica-cemented Kayenta Formation forms the cap rock for the Lower Jurassic carbonate-cemented Wingate Sandstone, which forms the impressive cliffs of the monument. The Upper Triassic Chinle Formation was deposited on the eroded and weathered Middle Proterozoic meta-igneous gneiss, pegmatite dikes, and migmatitic gneiss. Structurally the area is deceptively challenging. Nearly flat-lying strata on the plateau are folded by northwest-trending fault-propagation folds into at least two S-shaped folds along the mountain front of the plateau. Strata under Grand Valley dip at about 6 degrees to the northeast. In the absence of local evidence, the uplifted plateau is attributed to Laramide deformation by dated analogous structures elsewhere in the Colorado Plateau. The major exposed fault records high-angle reverse relationships in the basement rocks but dissipates strain as a triangular zone of distributed microfractures and cataclastic flow into overlying Mesozoic strata that absorb the fault strain, leaving only folds. Evidence for younger, probably late Pliocene or early Pleistocene, uplift does exist at the antecedent Unaweep Canyon south and east of the map area. To what degree this younger deformation affected the map area is unknown. Several geologic hazards affect the area. Middle and late Pleistocene landslides involving the smectite-bearing Brushy Basin Member of the Morrison Formation are extensive on the plateau and common in the Redlands below the plateau. Expansive clay in the Brushy Basin and other strata create foundation stability problems for roads and homes. Flash floods create a serious hazard to people on foot in narrow canyons in the monument and to homes close to water courses downstream from narrow restrictions close to the monument boundary.

Colorado↗
USGS1990

Role of heat and detachment in continental extension as viewed from the eastern basin and range province in Arizona

The Bill Williams River area of west-central Arizona includes not only the Rawhide-Buckskin metamorphic core complex, which is part of the lower Colorado River highly extended terrane (HET), but also the boundary between the extended terranes of the Basin and Range Province and the less deformed Arizona Transition Zone/Colorado Plateau. This provides important constraints on models that address the mechanisms for the mid- to late Tertiary deformation. Three phases of extension are present. The oldest is the extension associated with core-complex tectonism, which characteristically shows a lower plate composed of lineated mylonitic gneiss overlain by a detachment fault that is regionally nearly horizontal but undulates at the local scale. The fault in turn is overlain by an upper plate that includes Precambrian basement rocks, recrystallized Paleozoic sedimentary rocks, Mesozoic(?) metasedimentary and metavolcanic rocks of greenschist facies, and unaltered to hydrothermally altered syntectonic sedimentary and volcanic rocks of Miocene age. The upper plate is cut by closely spaced faults of modest structural relief that strike northwest and strongly rotate intervening blocks to face southwest. Most of these faults do not penetrate below the detachment fault. Fault spacing increases, and rotation decreases, to the northeast, away from the trace of the detachment. The second phase consists of “classic” Basin-Range high-angle normal faults that strike about north and have wide spacing, high structural relief, and modest rotation of blocks. These faults have no consistent direction of displacement and so produced horst and graben that form the ranges and basins visible today. This phase is locally superposed on Phase I, and also extends in more subdued form into the Transition Zone/Colorado Plateau. The third phase consists of tectonic quiescence and is present everywhere except parts of the Transition Zone that are still active seismically. The first phase occurred in the early and middle Miocene and was accompanied by deposition of syntectonic fluviolacustrine rocks (Suite I); the second (middle to late Miocene) was marked by interior-basin deposits (Suite II); the third (latest Miocene through Quaternary) is characterized by deposits related to through-flowing drainage. The phases grade into each other and thus are likely to be genetically related. Tectonic models must take into account not only the geographic distribution of deformation at any one time but also the time-dependent succession of deformation at any one place. A model proposed in this paper attempts to do this. The model is thermotectonic. A heating event in the lower crust, (basaltic intrusion, asthenospheric upwelling) combined with stretching, causes a sharp thermal front to rise within the crust. Embedded within the front is an “isotherm” that marks the brittle-ductile transition. As the front rises, it leaves behind a trail of shear zones, each marking a locus of preferred failure defined by mechanical or physical properties, or combinations thereof. The highest shear zone, now preserved in fossil form as the “detachment”, occurs where the front impinges on the meteoric groundwater, a few km below the topographic surface. The water steepens the thermal gradient at the front, which it stabilizes. A convective hydrothermal circulation system is established, causing alteration and mineralization above the ductile-brittle transition, as well as pore overpressure that results in hydrofracturing (producing monolithologic breccias) and the sliding of gravity-glide sheets. During these events, extension is taking place by brittle failure in the upper plate and ductile deformation below the detachment. Simultaneously, the hottest areas (core complexes) are updomed, promoting drainage reversals and the sliding of breccias and glide sheets. All this occurred only in the hottest areas or “blisters”, now marked by the core complexes. Distal areas showed less or no deformation at the surface. With time and the waning of the thermal event, the thermal front, and thus the brittle-ductile transition, smoothed out and sank, again leaving a trail of shear zones. Phase 1 deformation ceased and was replaced by Phase 2 deformation that occurred over a much wider area. Eventually, the front sank so deep that surface deformation ceased. This illustrates how the style of deformation at the surface may be a measure of the depth to the brittle-ductile transition. According to the thermotectonic model, extensional strain does not need to be constant along the detachment, in contrast to models involving simple shear through crustal-scale normal faults. On the contrary, one would expect strain to vary geographically as a function of maximum temperature attained, because of the well known relation between temperature and lithospheric strength. The thermotectonic model is also in good accord with geophysical characteristics of the Basin and Range Province, which suggests that extension was accompanied by intrusion of basalt into the lower crust, with consequent heating and anatexis. Many studies in the U.S. and elsewhere support the model by showing that continental extension commonly is accompanied by near-surface temperatures corresponding to the brittle-ductile transition, by steep thermal gradients, and by hydrothemal convective systems. A possible driving mechanism from the thermotectonic processes described by the model is the rise of asthenospheric domes or welts, which thin the lithosphere by subcrustal transfer while heating and stretching it. An asthenospheric welt that migrates northeastward while dying out might explain the encroachment of relatively subdued extension onto the Colorado Plateau, as well as the juxtaposition of compressive stress on the plateau with extensional stress in the adjacent Transition Zone and Basin and Range Province.

Arizona↗
USGS2005

Digital data and derivative products from a high-resolution aeromagnetic survey of the central San Luis basin, covering parts of Alamosa, Conejos, Costilla, and Rio Grande counties, Colorado, and Taos county, New Mexico

This report describes data collected from a high-resolution aeromagnetic survey flown over the central San Luis basin during October, 2004, by PRJ, Inc., on contract to the U.S. Geological Survey (USGS). The survey extends from just north of Alamosa, Colorado, southward to just northwest of Taos, New Mexico. It covers large parts of the San Luis Valley in Alamosa, Conejos, Costilla, and Rio Grande Counties, southern Colorado, and the Taos Plateau in Taos County, northern New Mexico. The survey was designed to complement two surveys previously acquired along the eastern borders of the San Luis Basin over the vicinities of Taos, New Mexico (Bankey and others, 2004a) and Blanca, Colorado (Bankey and others, 2004b). Our overall objective in conducting these surveys is to improve knowledge of the subsurface geologic framework in order to understand ground-water systems in populated alluvial basins along the Rio Grande. These USGS efforts are conducted in collaboration with other federal, state, and local governmental entities where possible.

Open-File Report↗
USGS1974

Meteoric water in magmas

Oxygen isotope analyses of sanidine phenocrysts from rhyolitic sequences in Nevada, Colorado, and the Yellowstone Plateau volcanic field show that δ 18 O decreased in these magmas as a function of time. This decrease in δ 18 O may have been caused by isotopic exchange between the magma and groundwater low in 18 O. For the Yellowstone Plateau rhyolites, 7000 cubic kilometers of magma could decrease in δ 18 O by 2 per mil in 600,000 years by reacting with water equivalent to 3 millimeters of precipitation per year, which is only 0.3 percent of the present annual precipitation in this region. The possibility of reaction between large magmatic bodies and meteoric water at liquidus temperatures has major implications in the possible differentiation history of the magma and in the generation of ore deposits.

Colorado, Nevada, Wyoming↗
USGS2002

Streamflow characteristics for selected stations in and near the Grand Mesa, Uncompahgre, and Gunnison National Forests, southwestern Colorado

The U.S Geological Survey, in cooperation with the Grand Mesa, Uncompahgre, and Gunnison National Forests, began a study in 2000 to develop selected streamflow characteristics for 60 streamflow-gaging stations in and near the Grand Mesa, Uncompahgre, and Gunnison National Forests. The study area is located in southwestern Colorado within the Gunnison River, Dolores River, and Plateau Creek Basins, which are tributaries of the Colorado River. In addition to presenting the compiled daily, monthly, and annual discharge data for the 60 stations, the report presents tabular and graphical results for the following computed streamflow characteristics: (1) Instantaneous peak-flow frequency; (2) flow duration for daily mean discharges on an annual (water year) basis and on a monthly basis, and flow duration for the annual and monthly mean discharges; (3) low-flow and high-flow frequency of daily mean discharges for periods of 1, 3, 7, 15, 30, 60, 120, and 183 consecutive days; and (4) annual and monthly mean and median discharges for each year and month of record, and frequency of the annual and monthly mean and median discharges. All discharge data and results from the streamflow-characteristics analyses are presented in Microsoft Excel workbooks on the enclosed CD-ROM.

Open-File Report↗
USGS1966

Geology of the Cerro Summit quadrangle, Montrose County, Colorado

The Cerro Summit quadrangle covers 58 square miles of dissected plateau on the south flank of the Gunnison uplift in southwestern Colorado. It lies east of the Uncompahgre River valley and south of the Black Canyon of the Gunnison River. Rocks dip gently in most of the quadrangle, but they are locally upturned and faulted on the margin of the Gunnison uplift and are intensely deformed in the core of the uplift. The rocks exposed are of Precambrian, late Mesozoic, and Cenozoic age. Precambrian rocks include metasedimentary schist and gneiss, granitic pegmatite, and olivine gabbro. The oldest Mesozoic rocks exposed are continental, fresh-water, and lagoonal deposits in the Late Jurassic Entrada Sandstone, Wanakah Formation, and Morrison Formation. Channel-fill deposits that unconformably overlie the Jurassic rocks are possibly the Burro Canyon Formation of Early Cretaceous age. Upper Cretaceous rocks include marine and nearshore deposits of the Dakota Sandstone, Mancos Shale, and Pictured Cliffs Sandstone, and the fresh- and brackish-water sandstone, shale, and coal of the Fruitland Formation. Rocks of Late Cretaceous age that crop out in the adjacent Cimarron Ridge area may also have been deposited in this quadrangle but are now eroded; these rocks include the nonmarine Kirtland Shale and an unnamed volcanic conglomerate and tuff breccia. Nine faunal zones in the Mancos Shale help to establish the correct correlation of units in the Upper Cretaceous. The Pictured Cliffs Sandstone, Fruitland Formation, and Kirtland Shale of the Cerro Summit area have been mapped by some geologists as the Mesaverde Formation. Fossils indicate that the rocks are younger than the type Mesaverde. The unnamed volcanic rocks represent major volcanism in nearby areas. A Late Cretaceous (Maestrichtian) age for the volcanism is indicated by palynological evidence and an isotopic age of approximately 66 million years. Middle Tertiary rocks are conglomerate and tuff breccia. Upper Tertiary or lower Quaternary rocks include gravel along Pool Gulch and older landslide debris on Waterdog Peak. Pleistocene and Recent deposits consist of the older stream gravel of Shinn Park, valley-fill deposits of Bostwick-Shinn Park, and pediment, landslide, eolian, alluvial, and colluvial deposits. P1elstocene valley-fill deposits of Bostwick-Shinn Park were deposited during the Cedar Ridge, or Kansan, to Pinedale or late Wisconsin times. The valley-fill deposits are divided into five units that are separated by strong Interglacial or Interstadial soils and that contain three volcanic ash beds. Chemical and petrographic data suggest that the middle ash bed may correlate with the Pearlette Ash Member (late Kansan) of the Sappa Formation in Nebraska. Alluvium on two pediment surfaces seems to be of Sacagawea Ridge or Illinoian age. Landslide deposits, of Pleistocene and Recent age, cover about 85 percent of the quadrangle; most of the deposits were formerly mapped as till. The name Cerro Till was abandoned because till does not occur in the type area. The dominant tectonic structures are the high-angle Cimarron fault of a few thousand feet displacement and the broad Montrose syncline. Evidence in the Cimarron Ridge area suggests that these structures formed in Late Cretaceous (Maestrichtian) time. Much of the strata near the surface of the quadrangle has been involved in landsliding that has continued from late Tertiary to the present.

Open-File Report↗
USGS2020

Water Quality of groundwater used for public supply in principal aquifers of the western United States

Groundwater provides nearly half of the Nation’s drinking water. As the Nation’s population grows, the importance of (and need for) high-quality drinking-water supplies increases. As part of a national-scale effort to assess groundwater quality in principal aquifers (PAs) that supply most of the groundwater used for public supply, the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Project staff sampled six principal aquifers in the western United States between 2013 and 2017: (1) the Basin and Range carbonate-rock aquifers, (2) Basin and Range basin-fill aquifers, (3) Rio Grande aquifer system, (4) High Plains aquifer, (5) Colorado Plateaus aquifers, and (6) Columbia Plateau basaltic-rock aquifers. These six PAs supply a large part of the Nation’s drinking water and cover a large geographic extent of the western conterminous United States. Groundwater samples were analyzed for a large suite of water-quality constituents including major ions, nutrients, trace elements, volatile organic compounds (VOCs), pesticide compounds, radioactive constituents, age tracers, and, in selected PAs, perchlorate. Two types of assessments were made: (1) a status assessment that describes the quality of the groundwater resource at time of collection and (2) an understanding assessment that evaluates relations between groundwater quality and potential explanatory factors that represent characteristics of the aquifer system. The assessments characterize untreated groundwater quality, which might be different than the quality of drinking water delivered to consumers. The assessments are based on water-quality data collected from 352 wells and 6 springs using an equal-area grid sampling design. This sampling approach allows for the estimation of the proportion of high, moderate, or low concentrations relative to federal water-quality benchmarks of selected constituents in the area of each PA. Results were compared to established benchmarks for drinking-water quality to provide context for evaluating the quality of untreated groundwater: Federal regulatory benchmarks for protecting human health, non-regulatory human-health benchmarks, and non-regulatory benchmarks for nuisance chemicals. Not all constituents that were analyzed have benchmarks and thus were not considered for assessments. Concentrations are characterized as high if they are greater than their benchmark. Concentrations are considered moderate if they are greater than one-half their benchmark (for inorganic constituents), or greater than one-tenth their benchmark (for organic constituents). Concentrations are considered low if they are less than moderate or the constituent was not detected. Status assessment results indicated that inorganic constituents more commonly occurred at high and moderate concentrations in the six PAs than organic constituents, and organic constituents predominately occurred at low concentrations. Inorganic constituents that exceeded health-based benchmarks (high concentrations) were present in all six PAs; aquifer-scale proportion were 30 percent in the Rio Grande aquifer system, 22 percent in the Basin and Range basin-fill aquifers, 20 percent in the Basin and Range carbonate-rock aquifers, 19 percent in the High Plains aquifer, 16 percent in the Colorado Plateaus aquifers, and 8 percent in the Columbia Plateau basaltic-rock aquifers. Arsenic, fluoride, manganese, and total dissolved solids were the constituents most commonly present at high concentrations. Organic constituents with human-health benchmarks (pesticide compounds and VOCs) did not occur at high concentrations and moderate concentrations were infrequent; aquifer-scale proportions ranged from 0 to 5 percent. Detections of organic compounds at low concentrations, however, occurred in all six PAs, with detection frequencies ranging from 10 to 26 percent for pesticide compounds and from 10 to 46 percent for VOCs. Specific organic constituents with detection frequencies greater than 10 percent were four herbicides (atrazine, didealkylatrazine, bromoform, and propazine), one insecticide (propoxur), and two VOCs (the trihalomethanes chloroform and bromodichloromethane). Where collected—in the Rio Grande aquifer system and High Plains aquifer—perchlorate did not occur at high concentrations; moderate aquifer-scale proportions were 3 and 11 percent, respectively. The understanding assessment included statistical tests to evaluate relations between constituent concentrations and potential explanatory factors to identify natural and human factors that affect groundwater quality. Potential explanatory factors included depth to bottom of well perforation, groundwater age category, land use, aquifer lithology, hydrologic conditions, and geochemical conditions. Higher concentrations of trace elements, radioactive constituents, and constituents with non-health-based benchmarks generally were associated with unconsolidated sand and gravel aquifer lithologies, premodern groundwater age, greater aridity, and more alkaline pH. Organic constituents with detection frequencies greater than 10 percent generally were associated with urban land use, shallower well depths, and higher total dissolved solids concentrations. The results for the six western PAs provide important insights into the quality of groundwater that is used for drinking water in the western United States, as well as natural and human factors that affect groundwater quality in this region.

Arizona, California, Colorado, Idaho, Kansas, Mont↗
USGS1979

Selected coal-related ground-water data, Wasatch Plateau-Book Cliffs area, Utah

The Wasatch Plateau-Book Cliffs%area as used in this report consists of about 8,000 square miles in east-central Utah. The major geographic features included in the area are the Wasatch Plateau, Book Cliffs, San Rafael Swell, Price River basin, and a small part of the Green River basin (pl. 1). The area is defined by approximate drainage-divide boundaries in the Wasatch Plateau and Book Cliffs, by an arbitrary boundary on the south, and by the Utah-Colorado State line on the east. The Wasatch Plateau-Book Cliffs area includes all the operating coal mines in Utah in 1978. Annual coal production in the area is expected to increase from the current (1978) rate of about 8 million tons to as much as 30 million tons within the next 10 years (J. W. Moffitt, U.S. Geological Survey, oral commun., 1978). Ground water is an important source of water supply in the area. As mining increases and mining-related municipalities grow, many sources of ground-water supply may be subjected to increased demands and possibly degradation of chemical quality. Waddell, Vickers, Upton, and Contratto (1978) reported some ground- water data after a reconnaissance of part of the area. The purpose of this report, which was prepared in cooperation with the U.S. Bureau of Land Management, is to present a more detailed compilation of ground-water-related data that were collected and compiled during October 1976 to March 1978. The report is designed to make the data available in an orderly and usable form for local and regional water managers and other users of water data.

Utah↗
USGS2012

Mojave Basin and Range Ecoregion: Chapter 29 in Status and trends of land change in the Western United States--1973 to 2000

This chapter has been modified from original material published in Sleeter and Raumann (2006), entitled “Land-cover trends in the Mojave Basin and Range Ecoregion” (U.S. Geological Survey Scientific Investigations Report 2006–5098). The Mojave Basin and Range Ecoregion (Omernik, 1987; U.S. Environmental Protection Agency, 1997) covers approximately 130,922 km 2 (50,549 mi 2 ) in the southwestern United States. The ecoregion, which encompasses parts of four states, includes the Mojave Desert and much of the other desert areas in southeastern California, as well as a large part of the southern Nevada desert (fig. 1). The ecoregion is bounded on the north by the Central Basin and Range Ecoregion, on the east by the Colorado Plateaus and the Arizona/New Mexico Plateau Ecoregions, on the south by the Sonoran Basin and Range Ecoregion, and on the west by the Southern California Mountains and the Sierra Nevada Ecoregions.

Arizona;California;Nevada;Utah↗
USGS2006

Structural fabrics, mineralization and Lamaride kinematics of the Idaho Springs-Ralston shear zone, Colorado mineral belt and central Front Range uplift

The Idaho Springs and Central City mining districts form the central portion of a structurally controlled hydrothermal precious- and base-metal vein system in the Front Range of the northeast-trending Colorado Mineral Belt. Three new 40Ar/39Ar plateau ages on hydrothermal sericite indicate the veins formed during the Laramide orogeny between 65.4??1.5 - 61.9??1.3 Ma. We compile structural geologic data from surface geological maps, subsurface mine maps, and theses for analysis using modern graphical methods and integration into models of formation of economic mineral deposits. Structural data sets, produced in the 1950s and 1960s by the U.S. Geological Survey, are compiled for fabric elements, including metamorphic foliations, fold axial trends, major brittle fault zones, quartz and precious- and base-metal veins and fault veins, Tertiary dikes, and joints. These fabric elements are plotted on equal-area projections and analyzed for mean fabric orientations. Strike-slip fault-vein sets are mostly parallel or sub-parallel, and not conjugate as interpreted by previous work; late-stage, normal-slip fault veins possibly show a pattern indicative of triaxial strain. Fault-slip kinematic analysis was used to model the trend of the Laramide maximum horizontal stress axis, or compression direction, and to determine compatibility of opening and shear motions within a single stress field. The combined-model maximum compression direction for all strike slip fault veins is ???068??, which is consistent with published Laramide compression directions of ???064?? (mean of 23 regional models) and ???072?? for the Front Range uplift. The orientations of fabric elements were analyzed for mechanical and kinematic compatibility with opening, and thus permeability enhancement, in the modeled regional east-northeast, Laramide compression direction. The fabric orientation analysis and paleostress modeling show that structural permeability during mineralization was enhanced along pre-existing metamorphic foliations and fold axial planes. Large orientation dispersion in most fabric elements likely caused myriad potential pathways for permeability. The dominant orientations of opening and shear mode structures are consistent with a sub-parallel network of structures that formed in the Laramide east-northeast compression direction. The results presented demonstrate the importance of using mechanical and kinematic theory integrated with contemporary ideas of permeability structure to better understand the coupled nature of fluid flow, mineral deposition, stress, and strain. Further, the results demonstrate that there is significant internal strain within this basement-cored uplift that was localized by optimally oriented pre-existing structures in a regional stress field.

Mountain Geologist↗
USGS2023

Environmental, morphological, and molecular data reveal a new species of freshwater mussel, Strophitus howellsi, endemic to the Edwards Plateau in Texas

Freshwater mussels are considered the most imperiled group of organisms in North America and systematics research has played an integral role in the development and implementation of their conservation. Despite the importance of systematics in conservation planning, the evolutionary relationships between many mussel taxa remain poorly explored, clearly illustrated by Strophitus undulatus . This species is wide-ranging, occurring in streams across the United States and Canada with a disjunct population in the Colorado River drainage in central Texas. The widespread distribution of S. undulatus , as well as high intraspecific morphological variation, has led previous authors to doubt the taxon is representative of a single species. In this study, we set out to investigate species boundaries in S. undulatus by integrating environmental, molecular, and morphological datasets. Molecular and morphological data supported S. undulatus from the Colorado River as distinct, which was supplemented by a species distribution modeling approach, suggesting potential adaptation to Edwards Plateau streams has contributed to speciation. Given our findings, we formally describe a new species of freshwater mussel, Strophitus howellsi , endemic to streams along the Edwards Plateau in the Colorado River drainage. A conservation assessment of S. howellsi suggests the species is extremely rare within a highly restricted distribution and may warrant future recovery actions. Our findings build on a growing body of literature highlighting aquatic endemism along the Edwards Plateau and have significant conservation implications for freshwater mussels in Texas.

Conservation Genetics↗
USGS1999

The importance of SAR wavelength in penetrating blow sand in Northern Arizona

Multifrequency and polarimetric Airborne Synthetic Aperture Radar (AIRSAR) images of a sand streak in northern Arizona demonstrate the ability of C- (6-cm wavelength), L- (24 cm), and P-band (68 cm) radar signals to backscatter, respectively, from increasingly greater depths reaching 2 m or more in active blow sand. The studied sand streak, located on a salient of Ward Terrace at lat 35??48.4'N and long 111??15.0'W, is sourced in the normally dry Little Colorado River channel and migrates northeastward toward the Moenkopi Plateau Scarp. The sand streak is 'radar dark' compared to the 'radar-bright' surface of Ward Terrace on all C-band images. It is, however, penetrated completely at P-band and is invisible on these images. The sand streak is recognizable on the LHH image but is poorly defined on the LHV image. High resolution AIRSAR images constitute the primary data set analyzed; in addition, a C-band radar image acquired by the European Remote Sensing (ERS) satellite is also presented. The spaceborne image data confirms the results of the aircraft data at C-band.Multifrequency and polarimetric Airborne Synthetic Aperture Radar (AIRSAR) images of a sand streak in northern Arizona demonstrate the ability of C- (6-cm wavelength), L- (24 cm), and P-band (68 cm) radar signals to backscatter, respectively, from increasingly greater depths reaching 2 m or more in active blow sand. The studied sand streak, located on a salient of Ward Terrace at lat 35??48.4???N and long 111??15.0???W, is sourced in the normally dry Little Colorado River channel and migrates northeastward toward the Moenkopi Plateau Scarp. The sand streak is `radar dark' compared to the `radar-bright' surface of Ward Terrace on all C-band images. It is, however, penetrated completely at P-band and is invisible on these images. The sand streak is recognizable on the LHH image but is poorly defined on the LHV image. High resolution AIRSAR images constitute the primary data set analyzed; in addition, a C-band radar image acquired by the European Remote Sensing (ERS) satellite is also presented. The spaceborne image data confirms the results of the aircraft data at C-band.

Remote Sensing of Environment↗
USGS2012

Colorado Plateaus Ecoregion: Chapter 21 in Status and trends of land change in the Western United States--1973 to 2000

The Colorado Plateaus Ecoregion covers approximately 129,617 km 2 (50,045 mi 2 ) within southern and eastern Utah, western Colorado, and the extreme northern part of Arizona (fig. 1). The terrain of this ecoregion is characterized by broad plateaus, ancient volcanoes, and deeply dissected canyons (Booth and others, 1999; fig. 2). The ecoregion is bounded on the east by the Wyoming Basin and Southern Rockies Ecoregions in Colorado and on the northwest by the Wasatch and Uinta Mountains Ecoregion in northern and central Utah. To the south, the ecoregion borders the Arizona/New Mexico Plateau Ecoregion, which has a higher elevation and more grasslands than the Colorado Plateaus Ecoregion (Omernik, 1987; U.S. Environmental Protection Agency, 1997).

Arizona;Colorado;New Mexico;Utah↗
USGS1995

Population trends of the loggerhead shrike from the North American Breeding Bird Survey

North American Breeding Bird Survey data indicated a general decline in Loggerhead Shrike (Lanius ludovicianus) populations during 1966-1993. At the continental level, shrikes declined at an average rate of 2.9% per year. Average rates of regional declines varied from 2.5-3.4% annually. These declines were prevalent in most states, provinces, and physiographic strata. Only the Edwards Plateau, High Plains, and Great Plains Roughlands strata, and Colorado, Louisiana, Montana, and South Dakota apparently have stable breeding populations. Severe winter weather during 1976-1979 may have contributed to this decline in the eastern half of the continent, combining with other factors during the winter and breeding seasons that have been implicated in the rangewide decline of this species.

Book chapter↗
USGS2012

Southern Rockies Ecoregion: Chapter 8 in Status and trends of land change in the Western United States--1973 to 2000

The Southern Rockies Ecoregion is a high-elevation mountainous ecoregion that covers approximately 138,854 km2 (53,612 mi2), including much of central Colorado and parts of southern Wyoming and northern New Mexico (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). It abuts six other ecoregions: the Wyoming Basin and Colorado Plateaus Ecoregions on the north and west, the Arizona/New Mexico Plateau Ecoregion on the south, and the Northwestern Great Plains, Western High Plains, and Southwestern Tablelands Ecoregions on the east (fig. 1). The ecoregion receives most of its annual precipitation (25–100 cm) as snowfall, which provides a significant amount of high-elevation snowpack that is an important water source for surrounding ecoregions. The Southern Rockies Ecoregion has a steep elevation gradient from low foothills to high peaks, with several hundred summits higher than 3,660 m (12,000 ft). As a southern extension of the larger RockyMountain system, it is composed primarily of seven main north-south trending mountain ranges that are separated by four large intermontane basins. A fifth basin, the San Luis Valley, is outside the ecoregion, forming a northern finger of the Arizona/New Mexico Plateau Ecoregion that lies mostly to the south. To the east, late Tertiary sand and gravel deposits that were eroded from the relatively young Rocky Mountains were carried eastward by streams, forming the nearby Western High Plains Ecoregion and its underlying Ogallala aquifer.

Colorado;New Mexico;Wyoming↗
USGS1961

Tertiary geology and oil-shale resources of the Piceance Creek basin between the Colorado and White Rivers, northwestern Colorado

The area of the Piceance Creek basin between the Colorado and White Rivers includes approximately 1,600 square miles and is characterized by an extensive plateau that rises 1,000 to more than 4,000 feet above the surrounding lowlands. Relief is greatest in Naval Oil-Shale Reserves Nos. 1 and 3 near the south margin of the area, where the spectacular Roan Cliffs tower above the valley of the Colorado River. The oldest rocks exposed in the mapped area are sandstone, shale, and coal beds of the Mesaverde group of Late Cretaceous age, which crop out along the east margin of the area. Overlying the Mesaverde is an unnamed sequence of dark-colored sandstone and shale, Paleocene in age. The Ohio Creek conglomerate, composed of black and red chert and quartzite pebbles in a white sandstone matrix, is probably the basal unit in the Paleocene sequence. The Wasatch formation of early Eocene age overlies the Paleocene sedimentary rocks. It is composed of brightly colored shale, lenticular beds of sandstone, and a few thin beds of fresh-water limestone. The Kasatch formation interfingers with and is overlain by the Green River formation of middle Eocene age. The Green River formation has been divided into the Douglas Creek, Garden Gulch, Anvil Points, Parachute Creek, and Evacuation Creek members. The basal and uppermost members, the Douglas Creek and Evacuation Creek, respectively, are predominantly sandy units. The two middle members, the Garden Gulch and Parachute Creek, are composed principally of finer clastic rocks. The Anvil Points member is present only on the southeast, east, and northeast margins of the area. It is a nearshore facies composed principally of sandstone and is the equivalent of the Douglas Creek, Garden Gulch, and the lower part of the Parachute Creek members. All of the richer exposed oil-shale beds are found in the Parachute Creek member, which is divided into two oil-shale zones by a series of low-grade oilshale beds. The upper oil-shale zone has several key beds and zones which can be traced throughout most of the mapped area. One of these, the Mahogany ledge or zone, is a group of very rich oil-shale beds at the base of the upper oil-shale zone. Drilling for oil and gas in the northeastern part of the area has revealed rich oil-shale zones in the Garden Gulch member also. Local unconformities within and at the base of the Evacuation Creek member are exposed at several places along Piceance Creek and at one place near the mouth of Yellow Creek; otherwise, the rock sequence is conformable. The mapped area is the major part of a large syncline, modified by numerous smaller structural features. Fractures, probably associated genetically with the minor structural features, are present in the central part of the area. These fractures are high-angle normal faults with small displacement. They occur in pairs with the intervening block downdropped. Two sets of joints are prominent, one trending northwest and the other northeast. The joint systems control the drainage pattern in the south-central part of the area. More than 20,000 feet of sedimentary rocks underlies the area. Many of the formations yield oil or gas in northwestern Colorado, northeastern Utah, and southwestern Wyoming. The Piceance Creek gas field, in which gas occurs in the Douglas Creek member of the Green River formation, is the largest oil or gas field discovered thus far within the area. About 7,000 million barrels of oil is contained in oil shale that yields an average of 45 gallons per ton from a continuous sequence 5 or more feet thick in the Mahogany zone. Oil shale in the Mahogany zone and adjacent beds that yields an average of 30 gallons of oil per ton from a continuous sequence 15 or more feet thick contains about 91,000 million barrels of oil. Similar shale in deeper zones in the northern part of the area, for which detailed estimates have not been prepared, are now known to contain at least an additional 72,000 million barrels of oil. Oil shale in a sequence 15 or more feet thick that yields an average of 25 gallons of oil per ton contains about 154,000 million barrels of oil in the Mahogany zone and adjacent beds; such shale in deeper zones in the northern part of the area probably contains at least an additional 157,000 million barrels of oil, although detailed estimates were not made. Oil shale in a sequence greater than 15 feet thick that yields an average of 15 gallons of oil per ton contains more than 900,000 million barrels of oil. These estimates of the oil content of the deposit do not take into account any loss in mining or processing of the shale.

Colorado↗