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At least 37 records · Page 2Linked to original sources
USGS2000

Age and Pb-Sr-Nd isotopic systematics of plutonic rocks from the Green Mountain magmatic arc, southeastern Wyoming: Isotopic characterization of a Paleoproterozoic island arc system

Three new U-Pb zircon ages and the Pb-Sr-Nd isotopic systematics of 24 whole-rock samples from mainly plutonic rocks of the Sierra Madre and Medicine Bow Mountains near the Colorado-Wyoming border help establish the Green Mountain magmatic arc as a Paleoproterozoic, variably eroded, island arc terrane. The Green Mountain magmatic arc, a terrane composed of variably metamorphosed volcanic and volcaniclastic rocks, minor metasedimentary rocks, high-grade gneisses, and plutons ranging from gabbro to granodiorite, was formed between ca. 1792 and 1744 Ma. It is the northernmost and oldest part of the Colorado province and is separated from Archean rocks to the north by the east-west-trending Cheyenne belt. New U-Pb zircon ages were determined for two dioritic samples of the Mullen Creek complex (1778 ±2 and 1778 ±17 Ma; an ultramafic/mafic layered intrusion) and for a sample of the Rambler granite (1771 ±3.4 Ma); both units are exposed in the Medicine Bow Mountains. A Sm-Nd internal isochron age of 1750 ±24 Ma (ϵ Nd i = + 3.8) was determined that is within error of the Sm-Nd whole-rock isochron age for the entire Lake Owen sample database (1775 ±45 Ma). Initial Nd signatures (+ 3.3 to 4.8) indicate that the bulk of the arc rocks was derived from a depleted mantle source at 1.78 Ga. Although the Rb-Sr systematics appear disturbed, data from extremely low Rb/Sr, non-hydrous, ultramafic layered units indicate an initial 87 Sr/ 86 Sr value of 0.7024. The range of initial Sr isotopic values for these rocks is elevated relative to depleted mantle sources at 1.78 Ga, an isotopic distinction of modern primitive oceanic island arc systems. The U-Pb data on the same mafic rock samples are consistent with the other isotopic results. The values define average initial Pb values of 206 Pb/ 204 Pb = 15.7 and 207 Pb/ 204 Pb = 15.3, indicative of a depleted mantle source at 1.78 Ga. Felsic plutonic arc rocks exhibit disturbed Pb and Sr isotopic behavior. They are characterized by the same depleted mantle signature with initial ϵ Nd values of ∼2.9–4.4, however, indicating little crustal contamination of source magmas for granites and precluding their derivation by subduction of Archean crustal components during collisional accretion of the arc.

Colorado, Wyoming↗
USGS2003

Tectonic evolution of the Proterozoic Colorado Province, Southern Rocky Mountains: A summary and appraisal

The Colorado province is a major component of a >1000-km-wide belt of Paleoproterozoic ocean-arc rocks that occupies the southwestern United States. Known as the Transcontinental Proterozoic provinces, this belt of largely juvenile rocks was added to the southern margin of the North American craton during the interval 1.8-1.70 Ga by convergent tectonism along the Cheyenne belt. A growing body of data suggests that these rocks were deposited, at least locally, on older rocks of earliest Proterozoic and Archean ages, probably correlative with the Trans-Hudson and Penokean orogens. The volcano-plutonic and associated sedimentary rocks of the Colorado province record two major, regional orogenies: (1) an older, protracted thermotectonic episode (1.78-1.70 Ga), named the Colorado orogeny, which involved mainly amphibolite-facies metamorphism during piecemeal assembly of various ocean-arc terranes; and (2) a younger, Mesoproterozoic intra-continental orogeny, named the Berthoud orogeny, which involved associated regional heating and A-type plutonism chiefly during the interval 1.45-1.40 Ga. The term "Colorado orogeny" is proposed for the regional Paleoproterozoic dynamothermal deformation. To distinguish differences in the geodynamics and ages of deformation and facilitate comparisons from place to place, type localities are proposed for separate phases or events of the Colorado orogeny. The central Front Range is suggested as a type area for the Berthoud orogeny, because the character and orientation of structures there are readily distinguished from those of the older Colorado orogeny.

Colorado↗
USGS2009

40Ar/39Ar dates for the Spanish Peaks intrusions in south-central Colorado

A diverse suite of spatially and temporally juxtaposed igneous rocks ranging from alkaline lamprophyres to granites intruded south-central Colorado during late Oligocene and early Miocene time. In addition to the stocks of the East and West Spanish Peaks, there are three types of dikes exposed in the region, based on orientation: radial, subparallel (striking approximately east–west), and independent dikes. The most striking features of this area are the numerous dikes radiating out from West Spanish Peak, some rising several tens of meters above the surrounding terrain and discontinuously exposed for tens of kilometers. New results from 40 Ar/ 39 Ar dating indicate that magmatism in the Spanish Peaks region began about 26.6 Ma and continued until about 21.8 Ma. Field evidence suggests that the initial intrusions were subparallel alkaline lamprophyre dikes south of the Spanish Peaks. A subsequent period of sub-alkaline magmatism occurred, producing West Spanish Peak (24.6 ± 0.13 Ma), East Spanish Peak (23.9 ± 0.08 Ma), and the radial dikes focused on West Spanish Peak. The final phase of magmatism included subparallel sub-alkaline lamprophyre dikes northeast of the Spanish Peaks. The 40 Ar/ 39 Ar results of this study substantiate the intrusive history derived from field relationships and establish the order of intrusion as West Spanish Peak, East Spanish Peak, and radial dikes, respectively. This study has implications for both the timing and style of the initiation of the Rio Grande rift, as well as the petrogenetic relationship between alkaline and sub-alkaline rocks in relatively stable cratonic areas.

Colorado, New Mexico↗
USGS2009

Structural development of high-temperature mylonites in the Archean Wyoming province, northwestern Madison Range, Montana

The Crooked Creek mylonite, in the northwestern Madison Range, southwestern Montana, is defined by several curved lenses of high non-coaxial strain exposed over a 7-km-wide, northeast-trending strip. The country rocks, part of the Archean Wyoming province, are dominantly trondhjemitic to granitic orthogneiss with subordinate amphibolite, quartzite, aluminous gneiss, and sills of metabasite (mafic granulite). Data presented here support an interpretation that the mylonite formed during a period of rapid, heterogeneous strain at near-peak metamorphic conditions during an early deformational event (D 1 ) caused by northwest–southeast-directed transpression. The mylonite has a well-developed L-S tectonite fabric and a fine-grained, recrystallized (granoblastic) texture. The strong linear fabric, interpreted as the stretching direction, is defined by elongate compositional “fish,” fold axes, aligned elongate minerals, and mullion axes. The margins of the mylonitic zones are concordant with and grade into regions of unmylonitized gneiss. A second deformational event (D 2 ) has folded the mylonite surface to produce meter- to kilometer-scale, tight-to-isoclinal, gently plunging folds in both the mylonite and country rock, and represents a northwest–southeast shortening event. Planar or linear fabrics associated with D 2 are remarkably absent. A third regional deformational event (D 3 ) produced open, kilometer-scale folds generally with gently north-plunging fold axes. Thermobarometric measurements presented here indicate that metamorphic conditions during D 1 were the same in both the mylonite and the country gneiss, reaching upper amphibolite- to lower granulite-facies conditions: 700 ± 50° C and 8.5 ± 0.5 kb. Previous geochronological studies of mylonitic and cross-cutting rocks in the Jerome Rock Lake area, east of the Crooked Creek mylonite, bracket the timing of this high-grade metamorphism and mylonitization between 2.78 and 2.56 Ga, nearly a billion years before the 1.78-Ga Big Sky orogeny, which overprinted the basement rocks exposed in adjacent ranges of the Wyoming province.

Montana↗
USGS2017

U-Pb ages and geochemistry of zircon from Proterozoic plutons of the Sawatch and Mosquito ranges, Colorado, U.S.A.: Implications for crustal growth of the central Colorado province

A broad study of zircons from plutonic rocks of the Sawatch and Mosquito ranges of west-central Colorado (U.S.A.) was undertaken to significantly refine the magmatic chronology and chemistry of this under-studied region of the Colorado province. This region was chosen because it lies just to the north of the suspected arc-related Gunnison-Salida volcano-plutonic terrane, which has been the subject of many recent investigations—and whose origin is still debated. Our new results provide important insights into the processes active during Proterozoic crustal evolution in this region, and they have important ramifications for broader-scope crustal evolution models for southwestern North America. Twenty-four new U-Pb ages and sequentially acquired rare-earth element (REE), U, Th, and Hf contents of zircon have been determined using the sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG). These zircon geochemistry data, in conjunction with whole-rock major- and trace-element data, provide important insights into zircon crystallization and melt fractionation, and they help to further constrain the tectonic environment of magma generation. Our detailed zircon and whole-rock data support the following three interpretations: (1) The Roosevelt Granite in the southern Sawatch Range was the oldest rock dated at 1,766 ± 7 Ma, and it intruded various metavolcanic and metasedimentary rocks. Geochemistry of both whole-rock and zircon supports the contention that this granite was produced in a magmatic arc environment and, therefore, is likely an extension of the older Dubois Greenstone Belt of the Gunnison Igneous Complex (GIC) and the Needle Mountains (1,770–1,755 Ma). Rocks of the younger Cochetopa succession of the GIC, the Salida Greenstone Belt, and the Sangre de Cristo Mountains (1,740–1,725 Ma) were not found in the Sawatch and Mosquito ranges. This observation strongly suggests that the northern edge of the Gunnison-Salida arc terrane underlies the southern portion of the Sawatch and Mosquito ranges. (2) Calc-alkalic to alkali-calcic magmas intruded this region approximately 55 m.y. after the Roosevelt Granite with emplacement of pre-deformational plutons at ca. 1,710 Ma (e.g., Henry Mountain Granite and diorite of Denny Creek), and this continued for at least 30 m.y., ending with emplacement of post-deformational plutons at ca. 1,680 Ma (e.g., Kroenke Granodiorite, granite of Fairview Peak, and syenite of Mount Yale). The timing of deformation can be constrained to sometime after intrusion of the diorite of Denny Creek and likely before the emplacement of the undeformed granite of Fairview Peak. Geochemistry of both whole-rock and zircon indicates that the older group of ca. 1,710-Ma plutons formed at shallower depths, and then they intruded the younger group of more deeply generated, commonly peraluminous and sodic plutons. Although absent in the Sawatch and Mosquito ranges, Mazatzal-age (ca. 1,680–1,620 Ma) plutonic rocks are present regionally. Inherited zircon components of Mazatzal-age were found as cores in some 1.4-Ga Sawatch and Mosquito Range zircons, indicating the likelihood of a relatively local source. These combined data suggest the possibility that all were produced within a continental-margin magmatic arc created as a result of southward-migrating (slab rollback?), north-dipping subduction to the south of the region. (3) Widespread Mesoproterozoic plutonism—with emplacement at various depths and exhibiting bimodal geochemistry—is recognized in 16 different samples. An older group of predominantly peraluminous, yet magnesian granitoids (e.g., granodiorite of Sayers, granite of Taylor River, and the St. Kevin Granite) were emplaced between ca. 1,450 and 1,425 Ma. These geochemical parameters suggest moderate degrees of partial melting in a low-pressure environment. Three younger metaluminous, but ferroan plutons (diorite of Grottos, diorite of Mount Elbert, and granodiorite of Mount Harvard), probably represent a final magmatic pulse at ca. 1,416 Ma. A comprehensive treatment of zircon REE and whole-rock trace-element behavior from Proterozoic rocks is scarce. Discriminant U/Yb versus Y diagrams using zircon data show that the Sawatch and Mosquito plutons are of continental origin, not oceanic. Additional bivariate diagrams incorporating cation ratio combinations of Gd, Ce, Yb, U, Th, Hf, and Eu offer refined insight into differences in fractionation trends and depth of magma generation for the various plutons. These interpretations, on the basis of zircon trace-element data, are mirrored in the whole-rock geochemistry data.

Colorado↗
USGS2018

40Ar/39Ar geochronology and petrogenesis of the Table Mountain Shoshonite, Golden, Colorado, U.S.A.

The Upper Cretaceous and Lower Paleogene Table Mountain Shoshonite lava flows and their proposed source, the Ralston Buttes intrusions, provide insight into the volcanic history of the Colorado Front Range. This study affirms the long-held hypothesis linking the extrusive Table Mountain lava flows and their intrusive equivalents at Ralston Buttes through major- and trace- element geochemistry. Systematic 40 Ar/ 39 Ar geochronology from all flows and intrusive units refines the eruptive history, improves precision on previously reported ages, and provides tighter constraints on the position of the K-Pg boundary in this location. Four flows are recognized on North and South Table mountains outside of Golden, Colorado. Flow 1 (66.5 ± 0.3 Ma, all ages reported with 2σ uncertainty) is the oldest, most compositionally distinct flow and is separated from younger flows by approximately 35 m of sedimentary deposits of the Denver Formation. Stratigraphically adjacent flows 2 (65.8 ± 0.2 Ma), 3 (65.5 ± 0.3 Ma), and 4 (65.9 ± 0.3 Ma) are compositionally indistinguishable. Lavas (referred to here as unit 5) that form three cone-shaped structures (shown by this study to be volcanic vents of a new unit 5) on top of North Table Mountain are compositionally similar to other units, but yield an age almost 20 m.y. younger (46.94 ± 0.15 Ma). Geochemistry and geochronology suggest that the rim phase of the Ralston plug (65.4 ± 0.2 Ma) is a reasonable source for flows 2, 3, and 4. All units are shoshonites—potassic basalts containing plagioclase, augite, olivine, and magnetite phenocrysts—and plot in the continental-arc field in tectonic discrimination diagrams. A continental-arc setting coupled with Late Cretaceous to early Paleogene ages suggest the high-K magmatism is associated with Laramide tectonism.

Colorado↗
USGS2022

Provenance of Devonian-Carboniferous strata of Colorado: The influence of the Cambrian and the Proterozoic

We report new LA-ICPMS U-Pb detrital zircon ages and sedimentary petrology of silty to sandy limestones and dolostones, as well as calcareous to dolomitic sandstones of the Devonian-Carboniferous (Mississippian) Chaffee Group, as well as detrital zircon ages from the Late Cambrian Sawatch Quartzite and a U-Pb zircon crystallization age on a late Mesoproterozoic (1087.9 13.5 Ma) granitoid of underlying basement from the Eagle basin of Colorado. Grain populations in the Chaffee Group are mostly bimodal, with over 84% of zircons centered around a Paleoproterozoic (ca. 1.78 Ga) mode typical of the Yavapai Province that forms much of the basement of Colorado and an early Mesoproterozoic (ca. 1.42 Ga) mode typical of A-type granites that intrude this region. A notable late Mesoproterozoic (ca. 1.08 Ga) mode exists in some Chaffee samples, giving those samples a trimodal detrital zircon age distribution. These bipartite or tripartite detrital zircon age modes exist in Cambrian, Devonian and Carboniferous strata from paleogeographically adjacent successions, but the correlation between the Chaffee zircons is highest with the regions basal Cambrian sandstones (Sawatch, Flathead, Ignacio formations) which have similar (1.08 Ga, 1.43 Ga, 1.71 Ga) zircon populations and a paucity of >1.8 Ga grains. This similarity suggests that the majority of grains in the Chaffee Group derive from recycling of these basal sandstones, and that little sediment was derived directly from then-exposed Precambrian basement highs, from the Wyoming Craton to the north, or from Paleoproterozoic arcs and orogens to the west and northeast. Minor Mesoarchean to early Paleoproterozoic (ca. 3.00 to 2.40 Ga) grains exist in the Chaffee Group, an attribute shared by the Late Ordovician Harding Sandstone of Colorados Front Range, but that is absent from the regions underlying Cambrian sandstonessuggesting some recycled mixture of Cambrian and Ordovician sedimentary rocks. No near-depositional age grains are present in the Chaffee Group; the youngest grain is Early Devonian (~417 Ma), >45 m.y. older than these strata, and Paleozoic grains are extremely uncommon (<0.1%; n=2927 grains).

Colorado↗
USGS2011

The U.S. Geological Survey's gravity program in the Rocky Mountain and Basin Range areas

Most of the gravity surveys of the U.S. Geological Survey have been support programs in connection with regional geologic structural studies, ground-water investigations, and heavy-metals exploration. Many of the studies were undertaken in conjunction with geological mapping and mineral investigations by the Survey's project geologists. Gravity data often complement aeromagnetic surveys to identify the sources of potential-field anomalies; other gravity data have been used to supplement high-resolution seismic and electrical investigations [ Mattick , 1967]. Geochemical follow-up has been fruitful in western Montana [ Mudge et al, 1967].

Arizona, Colorado, Idaho, Montana, Nevada, New Mex↗
USGS2014

Two decision-support tools for assessing the potential effects of energy development on hydrologic resources as part of the Energy and Environment in the Rocky Mountain Area interactive energy atlas

The U.S. Geological Survey project—Energy and Environment in the Rocky Mountain Area (EERMA)—has developed a set of virtual tools in the form of an online interactive energy atlas for Colorado and New Mexico to facilitate access to geospatial data related to energy resources, energy infrastructure, and natural resources that may be affected by energy development. The interactive energy atlas currently (2014) consists of three components: (1) a series of interactive maps; (2) downloadable geospatial datasets; and (3) decison-support tools, including two maps related to hydrologic resources discussed in this report. The hydrologic-resource maps can be used to examine the potential effects of energy development on hydrologic resources with respect to (1) groundwater vulnerability, by using the depth to water, recharge, aquifer media, soil media, topography, impact of the vadose zone, and hydraulic conductivity of the aquifer (DRASTIC) model, and (2) landscape erosion potential, by using the revised universal soil loss equation (RUSLE). The DRASTIC aquifer vulnerability index value for the two-State area ranges from 48 to 199. Higher values, indicating greater relative aquifer vulnerability, are centered in south-central Colorado, areas in southeastern New Mexico, and along riparian corridors in both States—all areas where the water table is relatively close to the land surface and the aquifer is more susceptible to surface influences. As calculated by the RUSLE model, potential mean annual erosion, as soil loss in units of tons per acre per year, ranges from 0 to 12,576 over the two-State area. The RUSLE model calculated low erosion potential over most of Colorado and New Mexico, with predictions of highest erosion potential largely confined to areas of mountains or escarpments. An example is presented of how a fully interactive RUSLE model could be further used as a decision-support tool to evaluate the potential hydrologic effects of energy development on a site-specific basis and to explore the effectiveness of various mitigation practices.

Colorado;New Mexico↗
USGS1995

Hydrogeologic data for the northern Rocky Mountains intermontane basins, Montana

The U.S. Geological Survey began a Regional Aquifer- System Analysis of the Northern Rocky Mountains Intermontane Basins of western Montana and central and central and northern Idaho in 1990 to establish a regional framework of information for aquifers in 54 intermontane basins in an area of about 77,500 square miles. Selected hydrogeologic data have been used as part of this analysis to define the hydro- logic systems. Records of 1,376 wells completed in 31 of the 34 intermontane basins in the Montana part of the study area are tabulated in this report. Data consist of location, alttiude of land surface, date well constructed, geologic unit, depth of well, diameter of casing, type of finish, top of open interval, primary use of water, water level, date water level measured, discharge, specific capacity, source of discharge data, type of log available, date water-quality parameters measured, specific conductance, pH, and temperature. Hydrographs for selected wells also are included. Locations of wells and basins are shown on the accompanying plate.

Open-File Report↗
USGS2007

2007 Rocky Mountain section Friends of the Pleistocene field trip - Quaternary geology of the San Luis basin of Colorado and New Mexico, September 7-9, 2007

Prologue Welcome to the 2007 Rocky Mountain Cell Friends of the Pleistocene Field Trip, which will concentrate on the Quaternary geology of the San Luis Basin of Colorado and New Mexico. To our best knowledge, Friends of the Pleistocene (FOP) has never run a trip through the San Luis Basin, although former trips in the region reviewed the 'Northern Rio Grande rift' in 1987 and the 'Landscape History and Processes on the Pajarito Plateau' in 1996. After nearly a decade, the FOP has returned to the Rio Grande rift, but to an area that has rarely hosted a trip with a Quaternary focus. The objective of FOP trips is to review - in the field - new and exciting research on Quaternary geoscience, typically research being conducted by graduate students. In our case, the research is more topically oriented around three areas of the San Luis Basin, and it is being conducted by a wide range of Federal, State, academic, and consulting geologists. This year's trip is ambitious?we will spend our first day mainly on the Holocene record around Great Sand Dunes National Park and Preserve, the second day on the Quaternary stratigraphy around the San Luis Hills, including evidence for Lake Alamosa and the 1.0 Ma Mesita volcano, and wrap up the trip's third day in the Costilla Plain and Sunshine Valley reviewing alluvial stratigraphy, the history of the Rio Grande, and evidence for young movement on the Sangre de Cristo fault zone. In the tradition of FOP trips, we will be camping along the field trip route for this meeting. On the night before our trip, we will be at the Great Sand Dunes National Park and Preserve's Pinyon Flats Campground, a group facility located about 2 miles north of the Visitors Center. After the first day's trip, we will dine and camp in the Bachus pit, about 3 miles southwest of Alamosa. For the final night (after day 2), we will bed down at La Junta Campground at the Bureau of Land Management (BLM) Wild and Scenic Rivers State Recreation Area, west of Questa, New Mexico, overlooking a majestic canyons of the Rio Grande and Red River. This is the 48th meeting of the Rocky Mountain Section of FOP, which was initiated by Gerry Richmond (USGS-Denver, deceased) in 1952 (see the following table, which lists all the Rocky Mountain Section field trips). The Rocky Mountain Section has been inactive for three years owing to a series of problems, including an unfortunate cancellation of Dennis Dahms' trip to the southern Wind River Range in 2005. Hopefully, this year's trip will provide the logistical initiative and scientific momentum for future Friends of the Pleistocene trips in the Rocky Mountain region.

Colorado, New Mexico↗
USGS2007

Geologic Map of the Albuquerque 30' x 60' Quadrangle, North-Central New Mexico

The Albuquerque 30' x 60' quadrangle spans the Rio Grande rift between the Colorado Plateau and Great Plains geologic provinces, and includes parts of the Basin and Range and Southern Rocky Mountain physiographic provinces. Geologic units exposed in the quadrangle range in age from Early Proterozoic schist and granite to modern river alluvium. The principal geologic features of the area, however, chiefly reflect contractional folding and thrusting of the Late Cretaceous Laramide orogeny and the Neogene extension of the Rio Grande rift. Significant parts of the history of the rift in this region are displayed and documented by the geology exposed in the Albuquerque quadrangle. Post-Laramide erosion, beginning at about 60 Ma, is recorded by the Diamond Tail and Galisteo Formations (upper Paleocene and Eocene) that are preserved in the Hagan Basin and around the uplifted margins of the younger Rio Grande rift. Intermediate volcaniclastic deposits of the Espinaso Formation (upper Eocene and Oligocene) were shed in and around the contemporaneous volcanic-intrusive complexes of the Ortiz porphyry belt in the northeastern part of the quadrangle. The earliest fluvial sediments attributed to extension in the Rio Grande rift in this area are the Tanos and Blackshare Formations (upper Oligocene and Miocene) in the Hagan Basin, which indicate extension was underway by 25 Ma. Farther west, the oldest rift-filling sediments are eolian sand and interdune silty deposits of the Zia Formation (lower to middle Miocene). Major extension occurred during the Miocene, but subsidence and sedimentation were highly irregular from place to place. Parts of three rift sub-basins are known within the Albuquerque quadrangle, each basin locally as deep as about 14,000 ft, separated by less-extended zones (structural horsts) where the rift fill is much thinner. The geometry of these early, deep rift sub-basins suggests the primary extension direction was oriented northeast-southwest. Significant local folding and uplift within the complex rift seems to have occurred in the late Miocene, accompanied by erosion and recycling of earlier rift-fill sediments. This deformation may reflect clockwise reorientation of the primary extension direction to its Pliocene and current east-west alignment. Late Miocene and early Pliocene uplift and erosion were widespread in the region, as indicated by channeled and local angular unconformities at the bases of all Pliocene units, especially prominent along basin margins. These Pliocene fluvial and alluvial deposits (Ceja and Ancha Formations and Tuerto Gravel) and the upper part of the Cochiti Formation are all conspicuously coarser grained than the Miocene beds they cover, particularly near source areas along the margins of the rift. These observations together indicate that the regional streams flowed at much greater discharge than the Miocene streams and that the Pliocene onset of cooler, wetter climate worldwide was the most likely cause. Despite these higher discharge conditions, it appears there was no Pliocene trunk stream through the rift valley because the youngest Pliocene beds in the basin center are largely fine grained sand, pebbly sand, and sandy silt. No Pliocene cobble-gravel deposits, or thick crossbed sets indicative of major stream discharge, have been documented in the basin center. Considerable evidence indicates significant erosion began in late Pliocene time, coincident with and following eruption of abundant basalt from several local centers at about 2.7-2.6 Ma. The onset of central valley erosion marks the initiation of the first through-flowing, high-energy trunk stream (the 'ancestral' Rio Grande), which most likely was caused by integration of drainage southward through the Socorro region. No upper Pliocene fluvial deposits have been identified in the valley center; rather, a significant unconformity separates beds with medial (or earliest late) Blancan fauna (older than about 2.2 Ma) from

Scientific Investigations Map↗
USGS1996

Selected geohydrologic data from a regional aquifer-system analysis of the Northern Rocky Mountains intermontane basins in Idaho

The U.S. Geological Survey began a regional aquifer-system analysis of the Northern Rocky Mountains of northern and central Idaho and western Montana in 1990. The analysis helped establish a regional framework of information for aquifers in about 70 ntermontane basins in an area of 80,000 square miles. In many areas, ground water is the only suitable source of supply, yet little information is available about this resource. Selected geohydrologic data from 1,004 wells in 19 intermontane basins in Idaho were compiled as part of the regional analysis. Data consist of basin name and well number, altitude of land surface, date of well construction, geologic unit, depth of well, diameter of casing, type of finish, top of open interval, primary use of water, date of water level measurement, water level, discharge, specific capacity, source of discharge data, type of log available, date of water-quality constituent measurement, specific conductance, pH, and temperature. A similar report for intermontane basins in Montana has been published by the U.S. Geologcial Survey in Montana. (USGS)

Idaho↗
USGS2007

Reported Historic Asbestos Mines, Historic Asbestos Prospects, and Natural Asbestos Occurrences in the Rocky Mountain States of the United States (Colorado, Idaho, Montana, New Mexico, and Wyoming)

This map and its accompanying dataset provide information for 48 natural asbestos occurrences in the Rocky Mountain States of the United States (U.S.), using descriptions found in the geologic literature. Data on location, mineralogy, geology, and relevant literature for each asbestos site are provided. Using the map and digital data in this report, the user can examine the distribution of previously reported asbestos occurrences and their geological characteristics in the Rocky Mountain States. This report is part of an ongoing study by the U.S. Geological Survey to identify and map reported natural asbestos occurrences in the U.S., which thus far includes similar maps and datasets of natural asbestos occurrences within the Eastern U.S. (http://pubs.usgs.gov/of/2005/1189/) and the Central U.S. (http://pubs.usgs.gov/of/2006/1211/). These reports are intended to provide State and local government agencies and other stakeholders with geologic information on natural occurrences of asbestos in the U.S.

Open-File Report↗
USGS2009

Core Research Center

The Core Research Center (CRC) of the U.S. Geological Survey (USGS), located at the Denver Federal Center in Lakewood, Colo., currently houses rock core from more than 8,500 boreholes representing about 1.7 million feet of rock core from 35 States and cuttings from 54,000 boreholes representing 238 million feet of drilling in 28 States. Although most of the boreholes are located in the Rocky Mountain region, the geologic and geographic diversity of samples have helped the CRC become one of the largest and most heavily used public core repositories in the United States. Many of the boreholes represented in the collection were drilled for energy and mineral exploration, and many of the cores and cuttings were donated to the CRC by private companies in these industries. Some cores and cuttings were collected by the USGS along with other government agencies. Approximately one-half of the cores are slabbed and photographed. More than 18,000 thin sections and a large volume of analytical data from the cores and cuttings are also accessible. A growing collection of digital images of the cores are also becoming available on the CRC Web site Internet http://geology.cr.usgs.gov/crc/.

General Information Product↗