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1
Watson, Ken, Lawrence C. Rowan, Timothy L. Bowers, Carmen Anton‐Pacheco, Pablo Gumiel, and Susanne H. Miller. "Lithologic analysis from multispectral thermal infrared data of the alkalic rock complex at Iron Hill, Colorado." GEOPHYSICS 61, no. 3 (May 1996): 706–21. http://dx.doi.org/10.1190/1.1443998.
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Airborne thermal‐infrared multispectral scanner (TIMS) data of the Iron Hill carbonatite‐alkalic igneous rock complex in south‐central Colorado are analyzed using a new spectral emissivity ratio algorithm and confirmed by field examination using existing 1:24 000‐scale geologic maps and petrographic studies. Color composite images show that the alkalic rocks could be clearly identified and that differences existed among alkalic rocks in several parts of the complex. An unsupervised classification algorithm defines four alkalic rock classes within the complex: biotitic pyroxenite, uncompahgrite, augitic pyroxenite, and fenite + nepheline syenite. Felsic rock classes defined in the surrounding country rock are an extensive class consisting of tuff, granite, and felsite, a less extensive class of granite and felsite, and quartzite. The general composition of the classes can be determined from comparisons of the TIMS spectra with laboratory spectra. Carbonatite rocks are not classified, and we attribute that to the fact that dolomite, the predominant carbonate mineral in the complex, has a spectral feature that falls between TIMS channels 5 and 6. Mineralogical variability in the fenitized granite contributed to the nonuniform pattern of the fenite‐nepheline syenite class. The biotitic pyroxenite, which resulted from alteration of the pyroxenite, is spatially associated and appears to be related to narrow carbonatite dikes and sills. Results from a linear unmixing algorithm suggest that the detected spatial extent of the two mixed felsic rock classes was sensitive to the amount of vegetation cover. These results illustrate that spectral thermal infrared data can be processed to yield compositional information that can be a cost‐effective tool to target mineral exploration, particularly in igneous terranes.
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Abu-Hejleh, Naser M., Michael W. O'Neill, Dennis Hanneman, and William J. Attwooll. "Improvement of the Geotechnical Axial Design Methodology for Colorado's Drilled Shafts Socketed in Weak Rocks." Transportation Research Record: Journal of the Transportation Research Board 1936, no. 1 (January 2005): 100–107. http://dx.doi.org/10.1177/0361198105193600112.
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Drilled shaft foundations embedded in weak rock formations support a large percentage of bridges in Colorado. Since the 1960s, empirical methods that entirely deviate from the AASHTO design methods have been used for the axial geotechnical design of these shafts. The margin of safety and expected shaft settlement are unknown in these empirical methods. Load tests on drilled shafts provide the most accurate design and research data for improvement of the design methods. Four Osterberg axial load tests were performed in Denver on drilled shafts embedded in soil-like claystone, very hard sandy claystone, and extremely hard clayey sandstone. An extensive program of simple geotechnical tests was performed at the load test sites, including standard penetration tests (SPT), unconfined compressive strength tests (UCT), and pressuremeter tests (PMT). Information on the construction and materials of the test shafts was documented, followed by thorough analysis of all test results. Conservative equations were suggested to predict the unconfined compressive strength and mass stiffness of weak rocks from SPT and PMT data. Colorado Department of Transportation (CDOT) and AASHTO–FHWA design methods for drilled shafts were thoroughly assessed. Design equations to predict the shaft ultimate unit base resistance ( qmax), side resistance ( fmax), and an approximate load–settlement curve as a function of the results of simple geotechnical tests were developed. The qualifications and limitations for using these design methods are presented (e.g., construction procedure, field conditions). Finally, a detailed strategic plan to identify the most appropriate design methods per LRFD for Colorado's drilled shafts was developed.
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Kadel-Harder, Irene M., Paul G. Spry, Audrey L. McCombs, and Haozhe Zhang. "Identifying pathfinder elements for gold in bulk-rock geochemical data from the Cripple Creek Au–Te deposit: a statistical approach." Geochemistry: Exploration, Environment, Analysis 21, no. 1 (October 26, 2020): geochem2020–048. http://dx.doi.org/10.1144/geochem2020-048.
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The Cripple Creek alkaline igneous rock-related, low-sulfidation epithermal gold telluride deposit, Colorado, is hosted in the 10 km wide Oligocene alkaline volcanic Cripple Creek diatreme in Proterozoic rocks. Gold occurs as native gold, Au-tellurides, and in the structure of arsenian pyrite, in potassically altered high-grade veins, and as disseminations in the host rocks.Correlation coefficients, principal component analysis, hierarchical cluster analysis and random forests were used to analyse major and trace element compositions of 995 rock samples primarily from low-grade gold mineralization in drill core from three currently operating pits (Wild Horse Extension, Globe Hill and Schist Island) in the northwestern part of the Cripple Creek diatreme. These methods suggest that Ag, As, Bi, Te and W are the best pathfinders to gold mineralization in low-grade disseminated ore. Although Mo correlates with gold in other studies and is spatially related to gold veins, molybdenite post-dated the formation of gold and is likely related to a late-stage porphyry overprint. These elements, in conjunction with mineralogical studies, indicate that tellurides, fluorite, quartz, carbonates, roscoelite, tennantite-tetrahedrite, pyrite, sphalerite, muscovite, monazite, bastnäsite and hübnerite serve as exploration guides to ore.
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Ward, Dylan J. "Dip, layer spacing, and incision rate controls on the formation of strike valleys, cuestas, and cliffbands in heterogeneous stratigraphy." Lithosphere 11, no. 5 (August 2, 2019): 697–707. http://dx.doi.org/10.1130/l1056.1.
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Abstract Landscapes developed over heterogeneous stratigraphy exhibit a spectrum of landforms from dramatic cliffbands to hogbacks, depending on the dip and spacing of the layers. In deeply incised landscapes, a single cliffband may consist of multiple resistant layers, whereas similar stratigraphy elsewhere is separated by strike valleys into individual cuesta benches or hogbacks. This paper presents a geometric analysis, informed by a numerical landscape model, to explain the conditions for development of a strike valley floored by erodible rocks. The results define a threshold incision rate below which strike valleys are more likely to form; this threshold incision rate is proportional to the stratigraphic spacing of cliff-forming layers and a trigonometric function of dip angle. The analysis also yields a time scale for the adjustment of structural landforms to changes in regional incision rate, which is a function of dip angle and the coupling between cliff retreat rate and escarpment height. In example landscapes of the Colorado Plateau, this time scale is likely much longer than that of documented variations of incision rates due to late Quaternary climate and land-use changes. The transitional state of escarpments in layered rock may therefore contain information about regional downcutting rates over time scales different from those recorded by the fluvial network. The utility of such features will require better understanding of the coupling between incision of a foot slope and the retreat rate of the cliff above in different kinds of rocks.
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Xu, Chen, Yujie Zhu, Danqing Song, Xiaogang Guo, Xiaoli Liu, Enzhi Wang, and Runhu Lu. "Comparison of DEM Models with Different Elemental Dimensions for TBM Disc Cutter Rock Fragmentation." Sustainability 14, no. 19 (October 10, 2022): 12909. http://dx.doi.org/10.3390/su141912909.
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Disc cutters are the dominant tool used in the excavation of hard rock formations in any underground construction application, such as when tunneling using tunnel-boring machines (TBM), as well as in shaft- and raise boring operations. Optimization of the cutting geometry of a given disc cutter for application in a rock formation often involves full-scale cutting tests, which is a difficult and costly proposition. An alternative to full-scale testing is the numerical simulation of TBM disc cutters for optimization under different settings. Recent efforts in the field of numerical simulations of rock cutting have shown the relative success of discrete element models, such as particle flow code (PFC), to simulate two- and three-dimensional rock fragmentation. This study is focused on a sensitivity analysis of PFC simulation of rock-cutting relative to the size of the elements. The calculated cutting forces were compared with the recorded forces under various conditions during full-scale tests using a linear cutting machine (LCM) on Colorado red granite (CRG). The estimated cutting coefficient and specific energy in the LCM tests and simulations showed good correlations, which validates the numerical simulation results. Two- and three-dimensional models showed that two-dimensional numerical models can offer a qualitative assessment of crack development, whereas three-dimensional models could be used to estimate the specific energy when cutting. The results can help in predicting the cutting forces in different rocks and ultimately improving disc-cutter geometry and cutter-head design.
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Riggs, N. R., T. B. Sanchez, and S. J. Reynolds. "Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA." Geosphere 16, no. 4 (June 30, 2020): 1042–57. http://dx.doi.org/10.1130/ges02193.1.
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Abstract A shift in the depositional systems and tectonic regime along the western margin of Laurentia marked the end of the Paleozoic Era. The record of this transition and the inception and tectonic development of the Permo-Triassic Cordilleran magmatic arc is preserved in plutonic rocks in southwestern North America, in successions in the distal back-arc region on the Colorado Plateau, and in the more proximal back-arc region in the rocks of the Buckskin Formation of southeastern California and west-central Arizona (southwestern North America). The Buckskin Formation is correlated to the Lower–Middle Triassic Moenkopi and Upper Triassic Chinle Formations of the Colorado Plateau based on stratigraphic facies and position and new detrital zircon data. Calcareous, fine- to medium-grained and locally gypsiferous quartzites (quartz siltstone) of the lower and quartzite members of the Buckskin Formation were deposited in a marginal-marine environment between ca. 250 and 245 Ma, based on detrital zircon U-Pb data analysis, matching a detrital-zircon maximum depositional age of 250 Ma from the Holbrook Member of the Moenkopi Formation. An unconformity that separates the quartzite and phyllite members is inferred to be the Tr-3 unconformity that is documented across the Colorado Plateau, and marks a transition in depositional environments. Rocks of the phyllite and upper members were deposited in wholly continental depositional environments beginning at ca. 220 Ma. Lenticular bodies of pebble to cobble (meta) conglomerate and medium- to coarse-grained phyllite (subfeldspathic or quartz wacke) in the phyllite member indicate deposition in fluvial systems, whereas the fine- to medium-grained beds of quartzite (quartz arenite) in the upper member indicate deposition in fluvial and shallow-lacustrine environments. The lower and phyllite members show very strong age and Th/U overlap with grains derived from Cordilleran arc plutons. A normalized-distribution plot of Triassic ages across southwestern North America shows peak magmatism at ca. 260–250 Ma and 230–210 Ma, with relatively less activity at ca. 240 Ma, when a land bridge between the arc and the continent was established. Ages and facies of the Buckskin Formation provide insight into the tectono-magmatic evolution of early Mesozoic southwestern North America. During deposition of the lower and quartzite members, the Cordilleran arc was offshore and likely dominantly marine. Sedimentation patterns were most strongly influenced by the Sonoma orogeny in northern Nevada and Utah (USA). The Tr-3 unconformity corresponds to both a lull in magmatism and the “shoaling” of the arc. The phyllite and upper members were deposited in a sedimentary system that was still influenced by a strong contribution of detritus from headwaters far to the southeast, but more locally by a developing arc that had a far stronger effect on sedimentation than the initial phases of magmatism during deposition of the basal members.
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Bracken, Kyle. "Mechanical stratigraphy and layer-bound normal faulting in the Upper Cretaceous Niobrara Formation, Wattenberg Field, Colorado." Mountain Geologist 57, no. 2 (April 1, 2020): 67–93. http://dx.doi.org/10.31582/rmag.mg.57.2.67.
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Layer-bound normal faults are pervasive within the very fine-grained rocks of the Upper Cretaceous Niobrara and Carlile formations in the Denver Basin. 3-D seismic and well log interpretation reveal a complex, segmented fault system that is divided into two discrete tiers: an upper tier located in the Pierre Shale, and a lower tier located in the Niobrara Formation. 3-D fault throw analysis shows maximum throw near the top of the Niobrara Formation with steep, asymmetrical throw gradient down section in the lower Niobrara and Carlile formations. Faults are laterally well-connected in the upper Niobrara Formation and commonly form linear arrays of linked graben systems. In contrast, faults deeper in the stratigraphic section that offset the Carlile and Greenhorn formations are more segmented and commonly form half grabens (as opposed to full, fault-bound grabens). In cross-section, fault planes measured from seismic have a general dip of 45°. However, close inspection reveals that faults consistently change dip angle as they pass through the lower Niobrara Formation, refracting from ~55° to ~35° through the Niobrara C Marl, then back up to ~50° in the Carlile and Greenhorn formations. The fault dip refraction produces a contractional step or bend in the fault plane associated with the lower dip segments. This geometry is investigated further with horizontal image logs and other borehole data to reveal a kinematic relationship between fault dip angle and mechanical stratigraphy. Field examples of normal faults that cut mechanically layered rock help better understand these complex fault geometries and provide reasonable inferences to their development and propagation history. In summary, it is argued that the mechanically layered nature of the Niobrara and Carlile formations is responsible for many of the fault characteristics described and provides valuable insight into understanding the fault system
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Groshong, Richard H., and Ken Kittleson. "Eastern Boulder-Weld fault zone, Colorado: A gravity slide with pop-up structures." Mountain Geologist 57, no. 3 (July 1, 2020): 177–98. http://dx.doi.org/10.31582/rmag.mg.57.3.177.
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The Boulder-Weld fault zone, located southeast of Boulder, Colorado, is about 10 km (6 mi) wide, 34 km (21 mi) long, and involves at least 335 m (1100 ft) of upper Cretaceous sedimentary rocks. It affects the Cretaceous upper Pierre Shale, Fox Hills Sandstone, and the coal–bearing lower Laramie Formation. This study is a detailed examination of the eastern portion of the fault zone which consists of undisturbed areas separated by three long, narrow, fault-bounded uplifts that have received a variety of interpretations over the years. The fault zone geometry is determined from 21 closely spaced cross sections that use more subsurface data than previous studies, incorporate the elevations of the major economic coal seam derived from a published composite structure-contour map, and are area balanced using area-depth-strain (ADS) analysis. The most common structural style is a pop-up structure in which the uplifts are bounded on both sides by reverse faults. At larger-displacement the pop-ups are at the tip of the ramp and a second fault has formed close to the base of the ramp. A few sections show simple ramp anticlines developed above listric thrusts. The lower detachment for all structures is the distinctive Kp2 marker in the upper Pierre Shale. ADS analysis of the best-controlled uplifts shows that the uplifts are area balanced and confirms the lower detachment to be near Kp2. The structures are interpreted to have formed as a gravity slide because they formed in a break-back sequence, a characteristic of gravity gliding, and because the transport direction is approximately down the current southeast dip of the Kp2 detachment.
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Velasco, Maria Soledad, David Alumbaugh, and Emmanuel Schnetzler. "Multiphysics data modeling and imaging for exploration in the southern Rocky Mountains." Interpretation 6, no. 3 (August 1, 2018): SG59—SG78. http://dx.doi.org/10.1190/int-2017-0215.1.
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We carried out a multidata geophysics study in southern Colorado to explore for [Formula: see text] reservoirs in an area where seismic imaging is very limited due to the mountainous terrain, the presence of high-velocity volcanic rocks, and difficulty in obtaining land access permits. We have developed a modeling/interpretation methodology using ground magnetotelluric data as well as airborne magnetic and electromagnetic data combined with public domain gravity data and existing well and seismic data. We used the integration of these data sets to produce a series of 2D and 3D geophysical models that reveal basin architecture previously poorly defined through the analysis of limited seismic and well data alone. We found that this type of analysis aids in decreasing uncertainty in the interpreted geologic cross sections and a better understanding of the structural complexities of the region. Through the application of machine learning methods, we are also able to integrate several data sets into a mathematical framework resulting in a predictive model of spatial [Formula: see text] distribution. The integration of the interpretations from all data sets, predictive analytics results, and knowledge of [Formula: see text] production, allows us to delineate areas of interest for further exploration.
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Allaz, Julien M., Joseph R. Smyth, Rhiana E. Henry, Charles R. Stern, Philip Persson, Joy J. Ma, and Markus B. Raschke. "Beryllium-silicon disorder and rare earth crystal chemistry in gadolinite from the White Cloud pegmatite, Colorado, USA." Canadian Mineralogist 58, no. 6 (November 1, 2020): 829–45. http://dx.doi.org/10.3749/canmin.1900084.
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ABSTRACT Gadolinite, REE2FeBe2Si2O10, is a monoclinic orthosilicate member of the gadolinite supergroup of minerals and occurs in beryllium and rare earth element (REE) bearing granites, pegmatites, and some metamorphic rocks. Gadolinite from the White Cloud pegmatite, South Platte Pegmatite district, Colorado, USA, has been investigated and shows unusually variable REE compositions and distinct Be-Si disorder. Crystal structure and chemistry of two petrographically distinct gadolinite samples from this locality have been studied by electron microprobe chemical analysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), single-crystal X-ray diffraction (XRD), and micro-Raman spectroscopy. Within these samples, the gadolinite was found to range from gadolinite-(Y) to gadolinite-(Ce). Regions of nearly full occupancy of Fe at the M site, and partial substitution of Si for Be at the Q tetrahedral site, as well as substitution of Be for Si at the T site were observed, with up to 15% vacancy at the Fe site and up to 15% disorder between Be and Si at distinct tetrahedral sites elsewhere. The layered nature of the crystal structure allows for large variation of the radius of the cation at the A site which contains the REE. This study shows that Be may substitute for Si and that Be may be more abundant in geochemical systems than previously assumed.
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Durrani, Bashir A., Diane I. Doser, G. R. Keller, and Thomas M. Hearn. "Velocity structure of the upper crust under the San Francisco volcanic field, Arizona." Bulletin of the Seismological Society of America 89, no. 1 (February 1, 1999): 239–49. http://dx.doi.org/10.1785/bssa0890010239.
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Abstract In addition to traditional in-line wide-angle seismic profiles, the 1989 Pacific to Arizona Crustal Experiment (PACE-1989) included some off-line shots and seismic recorders, which, along with the data from the main profiles, provide tomographic coverage of the late Cenozoic San Francisco volcanic field. This major volcanic center is interesting because of its location on the margin of the Colorado plateau and because of the diversity of the composition of the volcanics. We employed arrival times for the Pg phase to undertake a tomographic analysis of the structure of the upper crust. The tomographic image indicates high-velocity zones at upper crustal depths under the San Francisco Mountain region. The P-wave velocities within these zones are 6% higher than the surrounding basement rocks. Although other interpretations are possible, we believe that these high-velocity regions most likely represent igneous intrusions associated with the volcanic centers that formed the San Francisco volcanic field. Geologic studies indicate that these intrusions would be of intermediate to mafic composition. Gravity data in the San Francisco volcanic field area also indicate that these high-velocity regions are coincident with high-density bodies at upper crustal depths.
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Boak, Jeremy, Tengfei Wu, and Justin Birdwell. "Geochemical studies of the Green River Formation in the Piceance Basin, Colorado." Geosites 50 (September 1, 2022): 1–32. http://dx.doi.org/10.31711/ugap.v50i.114.
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The Eocene Green River Formation contains the largest oil shale deposits in the world and is a welldocumented example of a lacustrine depositional system. In addition, mineral resources associated with oil shale in the Piceance Basin nahcolite [NaHCO3] and dawsonite [NaAl(CO3)(OH)2)] are of current and potential economic value, respectively. Detailed geochemical analysis across the basin can aid in the understanding of the depositional environment, sedimentary processes, and water-chemistry evolution in this system. Quantitative geochemical data for Green River oil shale from the Piceance Basin of Colorado were collected by inductively coupled plasma optical emission spectroscopy and mass spectrometry as part of this study. The basin margin is represented by samples from exposures at Douglas Pass (Garfield County) and the basin center area is characterized by core samples from two drilled wells: the Shell 23X-2 and John Savage 24-1 (Rio Blanco County). Major elements and groups of elements are used as proxies for clastic influx (Si, Al, K, Ti), carbonate deposition (Ca, Mg), salinity (Na), paleo-productivity (P), and redox state (Fe, S), respectively. Minor and trace elements reinforce observations based on major elements, including Rb, Zr, Nb for clastic influx and Mn, Sr for carbonate. Trace elements are used to characterize redox conditions (As, Mo, U, V, Co, Ni, Cu, Zn) and salinity (Rb/K, B/Ga). Chemical distinctions between the basin margin and the basin center, in terms of these components and total organic carbon concentrations, support the model of a permanently stratified lake through most of the depositional interval. A primary purpose of the study was to conduct more extensive sampling to confirm conclusions of a previous reconnaissance study. Geochemical data from this study indicates elevated Na around the basin margin occurring earlier than in the deeper basin. Early in the history of Lake Uinta, the salinity may have been elevated first in the shallower marginal waters, due to increased evaporation, which then led to elevated salinity in the basin center through transport of saline density currents. Other indicators of salinity (Rb/K, B/Ga) do not track Na content in intervals where clay minerals are absent due to diagenetic alteration under hypersaline conditions but may be used to indicate the salinities at which authigenic Na-bearing minerals begin to form. Most Na-rich samples show high proportions of clastic constituents (Si, Al, K, Ti) compared to conventional carbonate constituents (Ca, Mg). Redox-sensitive period IV transition metal elements (V, Co, Ni, Cu, Zn) show only local occurrence of significant enrichment relative to average shale abundances. Analysis of Fe/Al ratios for this dataset suggests that the depletion of these elements may be related to source rocks depleted in mafic constituents, with apparent redox-related enrichments subdued by this effect. The basin margin samples reflect generally oxic bottom waters, with some intervals deposited under more reducing, possibly dysoxic to anoxic conditions. The basin center results indicate more reducing conditions, with Mo and U enrichment factors suggesting operation of a particulate shuttle mechanism that scavenged Mo on Fe/Mn-oxyhydroxides that redissolved at depth, with Mo precipitating along with sulfides and/or organic matter at or near the sediment/water interface.
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Thul, David, and Stephen Sonnenberg. "Expression of the Colorado Mineral Belt in Upper Cretaceous Niobrara Formation Source Rock Maturity Data from the Denver Basin." Mountain Geologist 55, no. 1 (January 2018): 19–52. http://dx.doi.org/10.31582/rmag.mg.55.1.19.
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New source rock maturity data along the Colorado Mineral Belt trend in the Denver Basin reveal that source rocks in the deepest portion of the basin range from the onset of oil generation to wet gas maturity across a distance of less than 30 miles along present day structure. Additionally, sampled rock core and cuttings along a northeast-southwest transect reveal that the Niobrara Formation is within the oil maturity window all the way to the Nebraska-Colorado border. The correlation of these analyses to an identified thermal anomaly demonstrate that maturity along these trends is affected by a historical increase in heat flow that can still be seen in the present-day bottom-hole temperatures. The identified maturity anomaly has significant implications for Niobrara prospectivity within the basin. Crossplotting, mapping, and numerical modeling show the onset of hydrocarbon maturity in the Niobrara is represented by 432 °C Tmax and that hydrocarbon expulsion occurs between 438 °C and 443 °C Tmax. In the Niobrara Formation of the Denver Basin there is a strong correlation between oil and gas shows, elevated bottom-hole temperatures (and thermal gradients), and geochemical maturity parameters. Through mapping of maturity and free hydrocarbon anomalies, more than 80% of the present day production can be predicted with source rock mapping.
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Faïn, X., D. Helmig, J. Hueber, D. Obrist, and M. W. Williams. "Mercury dynamics in the Rocky Mountain, Colorado, snowpack." Biogeosciences 10, no. 6 (June 13, 2013): 3793–807. http://dx.doi.org/10.5194/bg-10-3793-2013.
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Abstract. Gaseous elemental mercury (GEM) was monitored at the Niwot Ridge (NWT) Long-Term Ecological Research (LTER) site (Colorado, USA, 40° N) from interstitial air extracted from the snowpack at depths ranging from the snow surface to 10 cm above the soil. A highly dynamic cycling of mercury (Hg) in this mid-latitude snowpack was observed. Patterns were driven by both GEM production in surface snow and GEM destruction in the deeper snowpack layers. Thorough mixing and vertical transport processes were observed through the snowpack. GEM was photochemically produced near the snow-air interface throughout the entire winter, leading to enhanced GEM levels in interstitial air of surface snow of up to 8 ng m−3. During low-wind periods, GEM in surface snow layers remained significantly above ambient air levels at night as well, which may indicate a potential weak GEM production overnight. Analyses of vertical GEM gradients in the snowpack show that surface GEM enhancements efficiently propagated down the snowpack, with a temporal lag in peak GEM levels observed with increasing depth. Downward diffusion was responsible for much of these patterns, although vertical advection also contributed to vertical redistribution. Destruction of GEM in the lower snowpack layers was attributed to dark oxidation of GEM. Analysis of vertical GEM / CO2 flux ratios indicated that this GEM destruction occurred in the snow and not in the underlying soil. The strong, diurnal patterns of photochemical GEM production at the surface ultimately lead to re-emission losses of deposited Hg back to the atmosphere. The NWT data show that highest GEM surface production and re-emissions occur shortly after fresh snowfall, which possibly resupplies photoreducible Hg to the snowpack, and that photochemical GEM reduction is not radiation-limited as it is strong even on cloudy days.
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Faïn, X., D. Helmig, J. Hueber, D. Obrist, and M. M. Williams. "Mercury dynamics in the Rocky Mountain, Colorado, Snowpack." Biogeosciences Discussions 9, no. 11 (November 2, 2012): 15423–58. http://dx.doi.org/10.5194/bgd-9-15423-2012.
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Abstract. Gaseous Elemental Mercury (GEM) was monitored at the Niwot Ridge (NWT) long-term ecological research (LTER) site (Colorado, USA, 40° N) from interstitial air extracted from the snowpack at depths ranging from the snow surface to 10 cm above the soil. A highly dynamic cycling of mercury (Hg) in this mid-latitude snowpack was observed. Patterns were driven by both GEM production in surface snow and GEM destruction in the deeper snowpack layers. Thorough mixing and vertical transport processes were observed through the snowpack. GEM was photochemically produced near the snow-air interface leading to enhanced GEM levels in interstitial air of surface snow of up to 8 ng m−3. During low wind periods, GEM in surface snow layers remained significantly above ambient air levels at night as well, which may indicate a potential weak GEM production over night. Analysis of vertical GEM gradients in the snowpack show that surface GEM enhancements efficiently propagated down the snowpack, with a temporal lag in peak GEM levels observed with increasing depth. Downward diffusion was responsible for much of these patterns, although vertical advection also contributed to vertical redistribution. Destruction of GEM in the lower snowpack layers was attributed to dark oxidation of GEM. Analysis of vertical GEM/CO2 flux ratios indicated that this GEM destruction occurred in the snow and not in the underlying soil. The strong, diurnal patterns of photochemical GEM production at the surface ultimately lead to re-emission losses of deposited Hg back to the atmosphere. The NWT data show that highest of GEM production and emission occur shortly after fresh snowfall, indicating that fresh snow possibly resupplies photoreducible Hg to the snowpack.
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Ward, D. S., and W. R. Cotton. "Cold and transition season cloud condensation nuclei measurements in western Colorado." Atmospheric Chemistry and Physics 11, no. 9 (May 10, 2011): 4303–17. http://dx.doi.org/10.5194/acp-11-4303-2011.
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Abstract. Recent studies have shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud droplet nucleating aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentrations were measured for a 24-day period in Mesa Verde National Park, in September and October 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship was found for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements collected aboard the King Air platform during December 2009. A CCN closure attempt was performed and suggested that the sampled aerosol may have had a low hygroscopicity that changed little with the large-scale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with CCN number concentrations that varied slowly in time, and little in space along the Western Slope.
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Sahl, Jason W., Raleigh Schmidt, Elizabeth D. Swanner, Kevin W. Mandernack, Alexis S. Templeton, Thomas L. Kieft, Richard L. Smith, et al. "Subsurface Microbial Diversity in Deep-Granitic-Fracture Water in Colorado." Applied and Environmental Microbiology 74, no. 1 (November 2, 2007): 143–52. http://dx.doi.org/10.1128/aem.01133-07.
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ABSTRACT A microbial community analysis using 16S rRNA gene sequencing was performed on borehole water and a granite rock core from Henderson Mine, a >1,000-meter-deep molybdenum mine near Empire, CO. Chemical analysis of borehole water at two separate depths (1,044 m and 1,004 m below the mine entrance) suggests that a sharp chemical gradient exists, likely from the mixing of two distinct subsurface fluids, one metal rich and one relatively dilute; this has created unique niches for microorganisms. The microbial community analyzed from filtered, oxic borehole water indicated an abundance of sequences from iron-oxidizing bacteria (Gallionella spp.) and was compared to the community from the same borehole after 2 weeks of being plugged with an expandable packer. Statistical analyses with UniFrac revealed a significant shift in community structure following the addition of the packer. Phospholipid fatty acid (PLFA) analysis suggested that Nitrosomonadales dominated the oxic borehole, while PLFAs indicative of anaerobic bacteria were most abundant in the samples from the plugged borehole. Microbial sequences were represented primarily by Firmicutes, Proteobacteria, and a lineage of sequences which did not group with any identified bacterial division; phylogenetic analyses confirmed the presence of a novel candidate division. This “Henderson candidate division” dominated the clone libraries from the dilute anoxic fluids. Sequences obtained from the granitic rock core (1,740 m below the surface) were represented by the divisions Proteobacteria (primarily the family Ralstoniaceae) and Firmicutes. Sequences grouping within Ralstoniaceae were also found in the clone libraries from metal-rich fluids yet were absent in more dilute fluids. Lineage-specific comparisons, combined with phylogenetic statistical analyses, show that geochemical variance has an important effect on microbial community structure in deep, subsurface systems.
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Ward, D. S., and W. R. Cotton. "Cold and transition season cloud condensation nuclei measurements in western Colorado." Atmospheric Chemistry and Physics Discussions 10, no. 11 (November 12, 2010): 27631–72. http://dx.doi.org/10.5194/acpd-10-27631-2010.
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Abstract. Recent research has shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud-active aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentration were measured for a 24-day period in Mesa Verde National Park, climatologically upwind of the San Juan Mountains, in Sept. and Oct. 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements aboard the KingAir platform during December 2009. A CCN closure attempt was performed using the size distribution information and suggested that the sampled aerosol in general had low hygroscopicity that changed slightly with the large-scale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with a cloud active portion that varied slowly in time, and little in space along the Western Slope.
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Johnson, J. Bradley. "Phytosociology and gradient analysis of a subalpine treed fen in Rocky Mountain National Park, Colorado." Canadian Journal of Botany 74, no. 8 (August 1, 1996): 1203–13. http://dx.doi.org/10.1139/b96-145.
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The vegetation of a subalpine fen in Colorado was studied. Insight was sought into the community structure and factors influencing species distribution of a vegetation type heretofore undescribed in the southern Rocky Mountains. A vegetational gradient was evaluated using detrended correspondence analysis (DCA). Four types of vegetation were subjectively defined; these same types were distinguished by the DCA. DCA further revealed marked differences in the vegetation occurring on peat hummocks versus in hollows. Species composition was related to environment using canonical correspondence analysis (CCA). Water-table depth, hummock height, shading, groundwater temperature, and conductivity were significantly correlated with species distribution, accounting for 51% of the total species variance. Univariate regression was used to examine how tree density varied with environment. The above factors, except for shading and conductivity, were also significantly correlated with tree density. It is suggested that the peat hummocks that form on this moderate fen provide an environment similar to that of an ombrotrophic bog and that these "miniature bogs" form in areas unable to support expansive bogs. Further, these hummocks provide small-scale environmental heterogeneity that exerts a strong control over species composition that would not be evident in studies based on samples of a large areal extent. Keywords: Colorado, gradient analysis, ordination, heterogeneity, peatlands, phytosociology.
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Rovnak, Joel, Laura A. St. Clair, Elena Lian, Carley McAlister, Rushika Perera, and Randall J. Cohrs. "The 19th Rocky Mountain Virology Association Meeting." Viruses 12, no. 1 (January 11, 2020): 85. http://dx.doi.org/10.3390/v12010085.
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This autumn, 95 scientists and students from the Rocky Mountain area, along with invited speakers from Colorado, California, Montana, Florida, Louisiana, New York, Maryland, and India, attended the 19th annual meeting of the Rocky Mountain Virology Association that was held at the Colorado State University Mountain Campus located in the Rocky Mountains. The two-day gathering featured 30 talks and 13 posters—all of which focused on specific areas of current virology and prion protein research. The keynote presentation reviewed new tools for microbial discovery and diagnostics. This timely discussion described the opportunities new investigators have to expand the field of microbiology into chronic and acute diseases, the pitfalls of sensitive molecular methods for pathogen discovery, and ways in which microbiology help us understand disruptions in the social fabric that pose pandemic threats at least as real as Ebola or influenza. Other areas of interest included host factors that influence virus replication, in-depth analysis of virus transcription and its effect on host gene expression, and multiple discussions of virus pathology, epidemiology as well as new avenues of diagnosis and treatment. The meeting was held at the peak of fall Aspen colors, surrounded by five mountains >11,000 ft (3.3 km), where the secluded campus provided the ideal setting for extended discussions, outdoor exercise and stargazing. On behalf of the Rocky Mountain Virology Association, this report summarizes 43 selected presentations.
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Baker, William L., and Peter J. Weisberg. "Landscape Analysis of the Forest-Tundra Ecotone in Rocky Mountain National Park, Colorado*." Professional Geographer 47, no. 4 (November 1995): 361–75. http://dx.doi.org/10.1111/j.0033-0124.1995.00361.x.
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Baker, William L., and Peter J. Weisberg. "Landscape Analysis of the Forest-Tundra Ecotone in Rocky Mountain National Park, Colorado*." Professional Geographer 47, no. 4 (November 1, 1995): 361–75. http://dx.doi.org/10.1111/j.0033-0124.1995.361_a.x.
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Phillips, Stephen, and Hudson Hudson. "The Upper Cretaceous Rock Springs Formation of northwest Colorado." Geology of the Intermountain West 8 (January 17, 2022): 45–71. http://dx.doi.org/10.31711/giw.v8.pp45-71.
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The Upper Cretaceous Rock Springs Formation of the Mesaverde Group in northwestern Colorado, southwestern Wyoming, and northeastern Utah is composed of fluvial, deltaic, and marine sediments that record the regression of the Western Interior Seaway during the Early to Middle Campanian. Contemporaneous deposits are present along the eastern and southeastern margins of the Greater Green River Basin in Wyoming, but correlation across the basin is challenging. Analysis of a small (1-km-long), understudied outcrop in northwestern Colorado assists in bridging that gap. The outcrop consists of distal and proximal deltaic deposits, overlain by distributary-channel complexes within delta-plain deposits. Correlation panels based on subsurface wireline logs and outcrop gamma-ray profiles show that the deposits are younger than lithostratigraphically equivalent strata of the Rock Springs Formation in Utah and Wyoming. Regional nomenclature is introduced for the area, and it is shown that these deposits differ from better-documented, older Rock Springs Formation deposits in Utah and Wyoming by having a higher net sandstone percentage due to the presence of substantial distributary-channel complexes. This study benefits subsurface exploration efforts in the Greater Green River Basin by providing outcrop analogs of reservoir distribution and quality.
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Ling, Chi-Hai, Edward G. Josberger, and A. S. Thorndike. "Mesoscale Variability of the Upper Colorado River Snowpack." Hydrology Research 27, no. 5 (October 1, 1996): 313–22. http://dx.doi.org/10.2166/nh.1996.0012.
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In the mountainous regions of the Upper Colorado River Basin, snow course observations give local measurements of snow water equivalent, which can be used to estimate regional averages of snow conditions. We develop a statistical technique to estimate the mesoscale average snow accumulation, using 8 years of snow course observations. For each of three major snow accumulation regions in the Upper Colorado River Basin – the Colorado Rocky Mountains, Colorado, the Uinta Mountains, Utah, and the Wind River Range, Wyoming – the snow course observations yield a correlation length scale of 38 km, 46 km, and 116 km respectively. This is the scale for which the snow course data at different sites are correlated with 70 per cent correlation. This correlation of snow accumulation over large distances allows for the estimation of the snow water equivalent on a mesoscale basis. With the snow course data binned into 1/4° latitude by 1/4° longitude pixels, an error analysis shows the following: for no snow course data in a given pixel, the uncertainty in the water equivalent estimate reaches 50 cm; that is, the climatological variability. However, as the number of snow courses in a pixel increases the uncertainty decreases, and approaches 5-10 cm when there are five snow courses in a pixel.
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Hegmon, Michelle. "Pueblo I Ceramic Production in Southwest Colorado: Analyses of Igneous Rock Temper." KIVA 60, no. 3 (January 1995): 371–90. http://dx.doi.org/10.1080/00231940.1995.11758276.
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Gonzales, David. "New Constraints on the Timing and History of Breccia Dikes in the Western San Juan Mountains, Southwestern Colorado." Mountain Geologist 56, no. 4 (October 1, 2019): 397–420. http://dx.doi.org/10.31582/rmag.mg.56.4.397.
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In the western San Juan Mountains, clastic (breccia) dikes crop out in Paleozoic to Cenozoic rocks. The dikes are tabular to bifurcating masses up to several meters thick and are exposed on northwest or northeast trends for up to several kilometers. They are matrix- to clast-supported with angular to rounded pebble- to boulder-sized fragments that in most dikes are dominated by Proterozoic igneous and metamorphic rocks. U-Pb age analyses (n = 3) reveal a range of zircon ages in all samples with several containing high proportions of 1820 to 1390 Ma zircons. The majority of Proterozoic zircons are interpreted as direct contributions from basement rocks during breccia dike formation and emplacement. Field relations and U-Pb zircon analyses reveal that breccia dikes formed in intervals from 65 to 30 Ma (Ouray) and 27 to 12 Ma (Stony Mountain); some dikes are closely allied with mineralization. The dikes formed at depths over 500 meters where Proterozoic basement was fragmented, entrained, and transported to higher structural levels along with pieces of Paleozoic to Cenozoic rocks. A close spatial relationship exists between breccia dikes and latest Mesozoic to Cenozoic plutons. This is best exemplified near Ouray where clastic dikes share similar trends with ~65 Ma granodiorite dikes, and there is a clear transition from intrusive rocks to altered-brecciated plutons, and finally to breccia dikes. The preponderance of evidence supports breccia dike formation via degassing and explosive release of CO2-charged volatiles on deep fractures related to emplacement of 70 to 4 Ma plutons or mantle melts. In addition to breccia dikes, several post-80 Ma events in the region involved explosive release of volatile-charged magmas: 29-27 Ma calderas, ~25 Ma diatremes, and ~24 Ma breccia pipes. Causal factors for production of these gas-charged magmas remain poorly understood, but partial melting or assimilation of altered and metasomatized lithospheric mantle could have played a role.
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Kuckelman, Kristin A., Ricky R. Lightfoot, and Debra L. Martin. "The Bioarchaeology and Taphonomy of Violence at Castle Rock and Sand Canyon Pueblos, Southwestern Colorado." American Antiquity 67, no. 3 (July 2002): 486–513. http://dx.doi.org/10.2307/1593823.
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Violence and the role of violence have emerged recently as topics important to understanding the prehistory of the northern Southwest. Recent excavations at Castle Rock and Sand Canyon pueblos, two thirteenth-century sites in the Mesa Verde region of southwestern Colorado, bring new data to bear on these subjects. Field contexts and the results of bone and myoglobin analyses indicate that nonlethal and lethal violence occurred in both of these villages and that additional modifications to bodies and bones occurred near the time of death. Around A.D. 1280, at least eight individuals at Sand Canyon Pueblo died violently, and at least 41 individuals died at Castle Rock. During or after the warfare event that ended the occupation of Castle Rock, some bodies were dismembered, bones were broken, crushed, and heat altered; a few bones were reamed, and the end of one bone was polished. Several incidents of violence and probable anthropophagy (the consumption of human flesh) have been documented in the Mesa Verde region for the mid-A.D. 1100s; however, this analysis of violent events in the late A.D. 1200s establishes a critical link between probable anthropophagy and warfare, and links both with the depopulation of the region.
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Shepperd, Wayne D. "A Classification of Quaking Aspen in the Central Rocky Mountains Based on Growth and Stand Characteristics." Western Journal of Applied Forestry 5, no. 3 (July 1, 1990): 69–75. http://dx.doi.org/10.1093/wjaf/5.3.69.
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Abstract A classification procedure using stand growth data from 140 aspen stands throughout Colorado and southern Wyoming was developed using multivariate clustering and discriminant analysis techniques. Stands were grouped into seven logical stand classses that differed in age, stocking, productivity, or other characteristics. A method of assigning other stands to these classes is presented and applied to an independent data set. West. J. Appl. For. 5(3):69-75, July 1990.
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Schavran, Gabrielle. "Structural Features in the Huerfano Park Area, East Flank, Sangre de Cristo Range, Colorado." Mountain Geologist 22, no. 1 (January 1, 1985): 33–39. http://dx.doi.org/10.31582/rmag.mg.22.1.33.
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Laramide deformation along the east flank of the Sangre de Cristo Range, Colorado, has produced an imbricate thrust system with associated major folds in the Middle Pennsylvanian Minturn Formation, west of the town of Gardner. Thrusts dip 5 to 15 degrees to the west and are offset along strike by small tear faults. Major folds are inclined to overturned near the leading edges of the thrusts and become open and diminish in amplitude to the west, farther from the leading edges. Fold axes trend between N 10 Wand N 60 Wand plunge gently to the northwest or southeast. Tectonic transport was from west-southwest to east-northeast as interpreted from ma1or thrust and fold trends. Detailed analyses of minor structures such as bedding-plane thrusts, minor folds, and angle faults substantiate the style of deformation and the interpreted direction of transport Pennsylvanian sedimentary rocks were detached and thrusted, probably above a major decollement surface. Folds, bedding thrust reverse faults, and tear faults developed during thrusting and imbrication. Regionally, Precambrian rocks to the west in the Sangre de Cristo Range are interpreted to be allochthonous suggesting that the fold and thrust belt represents a zone of Laramide crustal shortening.
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Litaor, M. Iggy. "Spatial Analysis of Plutonium-239 + 240 and Americium-241 in Soils around Rocky Flats, Colorado." Journal of Environmental Quality 24, no. 3 (May 1995): 506–16. http://dx.doi.org/10.2134/jeq1995.00472425002400030018x.
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Griffith, Michael B., Brian H. Hill, Alan T. Herlihy, and Philip R. Kaufmann. "MULTIVARIATE ANALYSIS OF PERIPHYTON ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN COLORADO ROCKY MOUNTAIN STREAMS1." Journal of Phycology 38, no. 1 (February 2002): 83–95. http://dx.doi.org/10.1046/j.1529-8817.2002.01117.x.
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Boy, M., T. Karl, A. Turnipseed, R. L. Mauldin, E. Kosciuch, J. Greenberg, J. Rathbone, et al. "New particle formation in the front range of the Colorado Rocky Mountains." Atmospheric Chemistry and Physics Discussions 7, no. 6 (November 5, 2007): 15581–617. http://dx.doi.org/10.5194/acpd-7-15581-2007.
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Abstract. New particle formation is of interest because of its influence on the properties of aerosol population, and due to the possible contribution of newly formed particles to cloud condensation nuclei. Currently no conclusive evidence exists as to the mechanism or mechanisms of nucleation and subsequent particle growth. However, nucleation rates exhibit a clear dependence on ambient sulphuric acid concentrations and particle growth is often attributed to the condensation of organic vapours. A detailed study of new particle formation in the Front Range of the Colorado Rocky Mountains is presented here. Gas and particle measurement data for 32 days was analyzed to identify event days, possible event days, and non-event days. A detailed analysis of nucleation and growth is provided for four days on which new particle formation was clearly observed. Evidence for the role of sesquiterpenes in new particle formation is presented.
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Boy, M., T. Karl, A. Turnipseed, R. L. Mauldin, E. Kosciuch, J. Greenberg, J. Rathbone, et al. "New particle formation in the Front Range of the Colorado Rocky Mountains." Atmospheric Chemistry and Physics 8, no. 6 (March 17, 2008): 1577–90. http://dx.doi.org/10.5194/acp-8-1577-2008.
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Abstract. New particle formation is of interest because of its influence on the properties of aerosol population, and due to the possible contribution of newly formed particles to cloud condensation nuclei. Currently no conclusive evidence exists as to the mechanism or mechanisms of nucleation and subsequent particle growth. However, nucleation rates exhibit a clear dependence on ambient sulphuric acid concentrations and particle growth is often attributed to the condensation of organic vapours. A detailed study of new particle formation in the Front Range of the Colorado Rocky Mountains is presented here. Gas and particle measurement data for 32 days was analyzed to identify event days, possible event days, and non-event days. A detailed analysis of nucleation and growth is provided for four days on which new particle formation was clearly observed. Evidence for the role of sesquiterpenes in new particle formation is presented.
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Elias, Scott A. "Late Pleistocene and Holocene Seasonal Temperatures Reconstructed from Fossil Beetle Assemblages in the Rocky Mountains." Quaternary Research 46, no. 3 (November 1996): 311–18. http://dx.doi.org/10.1006/qres.1996.0069.
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Mutual Climatic Range (MCR) analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14,500 to 400 yr B.P. The fossil sites represent a transect of the Rocky Mountain region from northern Montana to central Colorado. The analyses yielded estimates of mean July and mean January temperatures. The oldest assemblage (14,500 yr B.P.) yielded mean July values of 10–11°C colder than present and mean January values 26–30°C colder than present. Postglacial summer warming was rapid, as indicated by an assemblage dating 13,200 yr B.P., with mean July values only 3–4°C cooler than modern. By 10,000 yr B.P., several assemblages indicate warmer-than-modern mean summer and winter values. By 9000 yr B.P., MCR reconstructions indicate that both summer and winter temperatures were already declining from an early Holocene peak. Mean July values remained above modern levels and mean January values remained below modern levels until 3000 yr B.P. A series of small-scale oscillations followed.
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Bigelow, Amy, Natalie Mladenov, David Lipson, and Mark Williams. "Dust deposition drives microbial metabolism in a remote, high-elevation catchment." Holocene 30, no. 4 (September 25, 2019): 589–96. http://dx.doi.org/10.1177/0959683619875191.
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In barren alpine catchments of the Colorado Rocky Mountains, microorganisms are typically carbon (C)-limited, and C-limitation can influence critical heterotrophic processes, such as denitrification. In these remote locations, organic matter deposited during dust intrusion events and other forms of aerosol deposition may be an important C source for heterotrophs; however, little is known regarding the biodegradability of atmospherically deposited organic matter. This study evaluated the extent to which organic matter in Holocene dust and other types of atmospheric deposition in the Colorado Rocky Mountains could support metabolic activity and be biodegraded by alpine bacteria. Microplate bioassays revealed that all atmospheric deposition samples were able to activate microbial metabolism. Decreases in dissolved organic carbon (DOC) concentrations over time in biodegradability incubations reflect the presence of two pools of dissolved organic matter (DOM), a rapidly decaying pool with rate constants in the range of 0.0130–0.039 d–1 and a slowly decaying pool with rate constants in the range of 0.0008–0.009 d–1. Changes in the fluorescence excitation-emission matrix of solutions evaluated over time indicated a transformation of organic matter by bacteria resulting in a more humic-like fluorescence signature. Fluorescence spectroscopic analyses, therefore, suggest that the degradation of non-fluorescent DOM in glutamate and dust-derived C sources by bacteria results in the production of fluorescent DOM.
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Liu, Tao, Lin Ji, Victor R. Baker, Tessa M. Harden, and Michael L. Cline. "Holocene extreme paleofloods and their climatological context, Upper Colorado River Basin, USA." Progress in Physical Geography: Earth and Environment 44, no. 5 (February 5, 2020): 727–45. http://dx.doi.org/10.1177/0309133320904038.
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Given its singular importance for water resources in the southwestern USA, the Upper Colorado River Basin (UCRB) is remarkable for the paucity of its conventional hydrological record of extreme flooding. Short-term record-based flood frequency analyses lead to very great aleatory uncertainties about infrequent extreme flood events and their climate-driven causal associations. This study uses paleoflood hydrology to examine a small portion of the underutilized, but very extensive natural record of Holocene extreme floods in the UCRB. We perform a meta-analysis of 82 extreme paleofloods from 18 slack water deposit sites in the UCRB to show linkages between Holocene climate patterns and extreme floods. The analysis demonstrates several clusters of extreme flood activity: 8040–7960, 4400–4300, 3600–3460, 2900–2740, 2390–1980, 1810–720, and 600–0 years BP. The extreme paleofloods were found to occur during both dry and wet periods in the paleoclimate record. When compared with independent paleoclimatic records across the Rocky Mountains and the southwestern USA, the observed temporal clustering pattern of UCRB extreme paleofloods shows associations with periods of abruptly intensified North Pacific-derived storms connected with enhanced variability of El Niño. This approach demonstrates the value of creating paleohydrological databases and comparing them with hydro-climatic proxies in order to identify natural patterns and to discover possible linkages to fundamental processes such as changes in climate.
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St Clair, Laura A., Ali L. Brehm, Shelby Cagle, Tillie Dunham, Jonathan Faris, Paul Gendler, Monica E. Graham, Sandra L. Quackenbush, Joel Rovnak, and Rushika Perera. "The 21st Annual Meeting of the Rocky Mountain Virology Association." Viruses 13, no. 12 (November 29, 2021): 2392. http://dx.doi.org/10.3390/v13122392.
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Nestled within the Rocky Mountain National Forest, 114 scientists and students gathered at Colorado State University’s Mountain Campus for this year’s 21st annual Rocky Mountain National Virology Association meeting. This 3-day retreat consisted of 31 talks and 30 poster presentations discussing advances in research pertaining to viral and prion diseases. The keynote address provided a timely discussion on zoonotic coronaviruses, lessons learned, and the path forward towards predicting, preparing, and preventing future viral disease outbreaks. Other invited speakers discussed advances in SARS-CoV-2 surveillance, molecular interactions involved in flavivirus genome assembly, evaluation of ethnomedicines for their efficacy against infectious diseases, multi-omic analyses to define risk factors associated with long COVID, the role that interferon lambda plays in control of viral pathogenesis, cell-fusion-dependent pathogenesis of varicella zoster virus, and advances in the development of a vaccine platform against prion diseases. On behalf of the Rocky Mountain Virology Association, this report summarizes select presentations.
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Levsen, Nicholas D., and Mark E. Mort. "Inter-simple sequence repeat (ISSR) and morphological variation in the western North American range of Chrysosplenium tetrandrum (Saxifragaceae)." Botany 87, no. 8 (August 2009): 780–90. http://dx.doi.org/10.1139/b09-038.
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The herbaceous perennial Chrysosplenium tetrandrum (Lund ex Malmgr.) Th. Fr. (Saxifragaceae) is a self-pollinating, circumpolar species with a broad latitudinal distribution and a disjunct North American range. The southernmost populations are isolated in the Rocky Mountains of Colorado and Montana, distantly separated from elements of the main range, which is largely coincident with known glacial refugia (e.g., Beringia) and recently deglaciated regions. We employed analyses of inter-simple sequence repeats (ISSRs) and morphology to determine patterns of variation within the western North American range of C. tetrandrum and test hypotheses of glacial population history and reproductive strategy. Analyses revealed very low estimates of range-wide genetic differentiation (θII = 0.085) and diversity (HS = 0.077, HT = 0.084), which are similar to levels found in other arctic plant species and have been primarily attributed to recent population establishment. Low levels of genetic differentiation among populations of Alaska (θII = 0.072), British Columbia (θII = 0.088), and Washington (θII = 0.058) suggest recent bottleneck or range expansion events. Both the Colorado and Alaska regions showed strong differentiation from each of the other regions, suggesting long-term isolation. The non-association between morphological and genetic variation indicates the effects of phenotypic plasticity or sexual reproduction.
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Anderson, R. Scott, Gonzalo Jiménez-Moreno, Thomas Ager, and David F. Porinchu. "High-elevation paleoenvironmental change during MIS 6–4 in the central Rockies of Colorado as determined from pollen analysis." Quaternary Research 82, no. 3 (November 2014): 542–52. http://dx.doi.org/10.1016/j.yqres.2014.03.005.
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AbstractPaleoecological studies from Rocky Mountain (USA) high elevations encompassing the previous interglacial (MIS 5e) are rare. The ~10-m composite profile from the Ziegler Reservoir fossil site (2705 m asl) of central Colorado allows us to determine paleoenvironments from Marine Oxygen Isotope Stages (MIS) 6– 4 using pollen zones that are approximately equivalent to marine oxygen isotope stages. During Pollen Zone (PZ) 6 time, pollen assemblages dominated by Artemisia (sagebrush) suggest that alpine tundra or steppe occurred nearby. The transition to PZ 5e was characterized by a rapid increase in tree pollen, initially Picea (spruce) and Pinus (pine) but also Quercus (oak) and Pseudotsuga menziesii (Douglas-fir). Non-arboreal pollen (NAP) types increased during PZ 5d, while Abies (fir) and Juniperus (juniper) increased during PZ 5c. Pollen evidence suggests that temperatures during PZ 5b were as cold as during PZ 6, with the site again surrounded by alpine tundra. Picea dominated during PZ 5a before the onset of cooler conditions during PZ 4. The MIS 6–MIS 5e transition here was similar to the MIS 2–MIS 1 transition at other Rocky Mountain sites. However, the Ziegler Reservoir pollen record contains evidence suggesting unexpected climatic trends at this site, including a warmer-than-expected MIS 5d and cooler-than-expected MIS 5b.
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Santi Malnis, Paula, Carina E. Colombi, Luis Martin Rothis, and Oscar Alcober. "Fluvial architecture and paleoenvironmental evolution of the Los Colorados Formation (Norian): Postrift stage of the Ischigualasto–Villa Unión Basin, NW Argentina." Journal of Sedimentary Research 90, no. 10 (October 1, 2020): 1436–62. http://dx.doi.org/10.2110/jsr.2020.65.
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ABSTRACT The last stage of activity of the Ischigualasto–Villa Unión Rift Basin in west-central Argentina is represented by the 1100-m-thick fluvial red-beds of the Los Colorados Formation (Norian). Facies and architectural-element analysis were applied and vertical stacking patterns evaluated in the Los Colorados Formation to develop a depositional model for the postrift stage of basin fill. The Los Colorados Formation is subdivided into eleven stratigraphic intervals, generally characterized by multistory and multilateral channelized bodies interspersed with thick floodplain deposits developed under seasonal semihumid to semiarid climate conditions. The evolution of the fluvial architectural style shows changes in the location of channel facies concentration, in paleocurrents, and sediment provenance from the sixth stratigraphic interval toward the upper part of the Los Colorados Formation. The fluvial architecture observed in the upper part exhibits a drift in paleocurrents from a SE to a NE mean direction, together with a radial pattern in paleocurrent directional data. Thus, the paleoenvironmental evolution of the Los Colorados Formation is interpreted in terms of axial vs. transverse drainage system fluvial architecture under ongoing postrift conditions. While the fluvial architecture of the lower part responds to an axial fluvial system, the upper part is compatible with the entrance of a fluvial transverse drainage system. The role of axial vs. transverse drainage systems is discussed in the Los Colorados Formation paleoenvironmental evolution. Despite the axial system being considered the main sediment feeder of the basin fill in most interpretations of the rock record, our results indicate that transverse drainage systems can play a central role in postrift basin filling, as is proposed in modern examples.
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Kitchell, Jennifer A. "Basketmaker and Archaic Rock Art of the Colorado Plateau: A Reinterpretation of Paleoimagery." American Antiquity 75, no. 4 (October 2010): 819–40. http://dx.doi.org/10.7183/0002-7316.75.4.819.
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A new cognitive model is proposed and applied to the analysis of the anthropomorphic-dominated paleoimagery or rock art of both the Archaic Barrier Canyon Style and the Basketmaker San Juan Style of the Colorado Plateau, including the attributes of headdresses and messengers. Under the cognitive model, the decision to execute rock art is culturally and historically conditioned; the interaction of narrative language and visual imagery takes precedence over hallucinatory and trance mechanisms. The cognitive model examines the interplay between perceptual imagery and stored mental imagery, both of which occur within the human cognitive system. Such an interplay arguably has been as important in the shaping of human cultures as the role of language. These Archaic and Basketmaker ecologies and cultures also may have developed group ritual, an early adoption not requisitely tied to the transition from a mobile hunter-gatherer ecology to an agricultural ecology. Such interpretations redefine the predominant images of the region's Archaic and Basketmaker anthropomorphic figures, bird-headed imagery, messenger spirits, supplication panels, and processional panels. The model reinstates the praejudico role that visual imagery plays in the construction of culture.
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Johnson, J. Bradley, and David A. Steingraeber. "The vegetation and ecological gradients of calcareous mires in the South Park valley, Colorado." Canadian Journal of Botany 81, no. 3 (March 1, 2003): 201–19. http://dx.doi.org/10.1139/b03-017.
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The vegetation, environment, and ecological gradients present on three calcareous mires in the South Park valley, Park County, Colorado, were investigated. Vegetation was classified into four habitat classes, nine subclasses, and twelve species associations using two-way species indicator analysis (TWINSPAN). Detrended correspondence analysis (DCA) was used to ordinate vegetation samples along two axes representing the three predominant ecological gradients: water table height, miremargin to expanse, and region. Canonical correspondence analysis (CCA) was used to directly relate local environmental conditions to vegetation. Water table depth, microtopographical development, soil and water pH and nutrient level, soil organic matter, and hydraulic head were significantly correlated with vegetation gradients. The mire soils consist of intermixed areas of organic and mineral soils. Mire soils and water are highly alkaline and nutrient-rich. Mean pore water calcium concentration on these mires is 115 mg/L, electrical conductivity averages 575 µS, and mean pH is 7.4. Owing to these conditions, the fen floras include a number of highly minerophilic species. Based on water chemistry and species criteria, each site was classified as rich to extremely rich fen, with the two fen types mixing in complex patterns according to local environmental conditions. The species Trichophorum pumilum, Salix candida, Salix myrtillifolia, Carex microglochin, Carex viridula, Carex scirpoidea, Eriophorum gracile, Triglochin maritimum, Triglochin palustris, Kobresia myosuroides, Kobresia simpliciuscula, Thalictrum alpinum, Scorpidium scorpioides, Scorpidium turgescens, and Calliergon trifarium were determined to be indicative of extremely rich fen conditions in the southern Rocky Mountains.Key words: Colorado, canonical correspondence analysis, detrended correspondence analysis, extremely rich fen, gradient analysis, mire.
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Pavlacky, David C., and Stanley H. Anderson. "Habitat Preferences of Pinyon-Juniper Specialists Near the Limit of Their Geographic Range." Condor 103, no. 2 (May 1, 2001): 322–31. http://dx.doi.org/10.1093/condor/103.2.322.
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Abstract We investigated habitat preferences for five pinyon-juniper specialists during the 1998 and 1999 breeding seasons in Utah juniper (Juniperus osteosperma) woodlands of southwestern Wyoming. We compared avian use and availability of vegetation features using univariate and multivariate analysis to detect selection for vegetative features of pinyon-juniper specialists near the northeastern range boundary of pinyon-juniper habitat on the Colorado Plateau. Gray Flycatchers (Empidonax wrightii), Juniper Titmice (Baeolophus griseus), and Bewick's Wrens (Thryomanes bewickii) preferred woodlands with high overstory juniper cover. The Juniper Titmouse was associated with senescent trees, Blue-gray Gnatcatcher (Polioptila caerulea) with rock outcrops and shrubs in the family Rosaceae, and Black-throated Gray Warbler (Dendroica nigrescens) with pinyon pine (Pinus edulis). We suggest the geographic distribution of four of five pinyon-juniper specialists is limited by the occurrence of pinyon pine in semiarid woodlands on the northeastern Colorado Plateau. The geographic limit for Blue-gray Gnatcatchers in this region may correspond to the presence of mountain mahogany in the woodland understory. The conservation of pinyon-juniper specialists in southwestern Wyoming will benefit from the maintenance of successional processes, particularly those that perpetuate mature woodlands with a pinyon pine component.
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Weisberg, Peter J., and William L. Baker. "Spatial variation in tree regeneration in the forest-tundra ecotone, Rocky Mountain National Park, Colorado." Canadian Journal of Forest Research 25, no. 8 (August 1, 1995): 1326–39. http://dx.doi.org/10.1139/x95-145.
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Ecotone vegetation may be especially sensitive to climate change. In particular, the invasion of subalpine meadows by tree seedlings has been well documented. However, there has been no systematic analysis of tree regeneration across the environmental heterogeneity of the alpine forest–tundra ecotone (FTE). Also, the position of the FTE may be relictual from more favorable climates of the past and therefore unresponsive to changing climate. To assess the environmental controls on FTE tree regeneration, to determine whether the ecotone might be relictual, and to determine whether tree invasion of nonforested FTE areas is occurring, we measured tree regeneration in various environments within the FTE of Rocky Mountain National Park, Colorado. Generally, seedling establishment appears to be controlled by patterns of soil moisture. Little seedling establishment was observed in krummholz openings, except for high seedling densities in willow wetlands. Tree seedling invasion of tundra is rare. Therefore, the upper limits of the FTE in Rocky Mountain National Park may be relictual from more favorable climates of the past. Abundant seedling establishment in patch forest openings suggests that patch forest may be poised to change to closed forest.
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Knowles, Peggy, and Michael C. Grant. "Genetic variation of lodgepole pine over time and microgeographical space." Canadian Journal of Botany 63, no. 4 (April 1, 1985): 722–27. http://dx.doi.org/10.1139/b85-091.
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The genetic composition of Pinus contorta var. latifolia as determined by isozyme analysis was examined in terms of its variation over space and time. Four populations of lodgepole pine consisting of approximately 125 trees each were sampled along an elevational gradient spanning a distance of 2 km in the Front Range of the Rocky Mountains in Colorado. Four isozymes were electrophoretically resolved from needle tissue removed from each tree. Ages were estimated from ring counts of either a tree core or a basal cross section of each tree. Gene frequencies were submitted to two-way analyses of variance using a subsampling procedure to generate multiple estimates within each cell. Analyses were performed to examine the variation in gene frequencies for each of the seven alleles resolved, using site (spatial) and age (temporal) as the independent factors. The results indicated that spatial heterogeneity contributes more to variation in genetic composition of lodgepole pine than does temporal heterogeneity. These results support theoretical proposals that spatial environmental heterogeneity under certain conditions can have more effect on variation in genetic composition than does temporal heterogeneity. It is further concluded that under certain conditions the analysis of variance procedure can be a useful analytic tool for examining gene frequency differences.
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James, Sarah E., and Robert T. M'Closkey. "Patterns of microhabitat use in a sympatric lizard assemblage." Canadian Journal of Zoology 80, no. 12 (December 1, 2002): 2226–34. http://dx.doi.org/10.1139/z02-212.
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The distribution of animals among habitats and microhabitats has frequently been used to examine patterns of niche overlap. We characterized microhabitat differences within an assemblage of four phrynosomatine lizard species (Sceloporus graciosus, Sceloporus undulatus, Urosaurus ornatus, and Uta stansburiana) that are commonly syntopic in the pinyon pine juniper woodland habitat on the elevated mesas of western Colorado. We censused lizard populations and recorded microhabitat characteristics of areas surrounding capture sites within Colorado National Monument, U.S.A. Discriminant function analysis of microhabitat features extracted two significant roots, explaining 89% of the microhabitat variation observed among species. Planned comparisons of canonical scores revealed two significant microhabitat niche differences. First, the microhabitat niche of U. ornatus was distinguished from those of all the other species by higher perch height and more vertical substrate, indicating this species' arboreality. Second, the microhabitat niche of S. graciosus was distinguished from those of the other species by having more flatland and less rock, indicating the use of more open flat sandy areas within the pinyon pine juniper woodland by this terrestrial species. Although the observed differences in microhabitat may influence the coexistence of these ecologically similar species, changes in relative abundance of the species over time suggest alternative mechanisms of coexistence.
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Peterson, David L., Michael J. Arbaugh, and Lindsay J. Robinson. "Effects of ozone and climate on ponderosa pine (Pinusponderosa) growth in the Colorado Rocky Mountains." Canadian Journal of Forest Research 23, no. 9 (September 1, 1993): 1750–59. http://dx.doi.org/10.1139/x93-221.
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Long-term radial growth trends of ponderosa pine (Pinusponderosa var. scopulorum) were studied in second-growth stands in the Front Range of the Colorado Rocky Mountains to determine if there has been any impact from oxidant air pollution. Although ozone concentrations are relatively high at some locations, visible pollutant injury was not found in any trees. Time series of basal area increments are generally homogeneous within stands. Concurrent periods of increasing and decreasing growth can be found in stands throughout the Front Range, which indicates that there are temporal growth trends at the regional level. Most of these trends appear to be related to the effects of stand dynamics and climate. Correlation analysis with climatic variables indicates that soil moisture supply is the dominant factor controlling interannual variation of basal area growth. Palmer hydrological drought index is highly correlated (positively) with growth during the summer months; total precipitation in spring is positively correlated with growth, and mean temperature in spring is negatively correlated with growth. There are no recent changes in growth trends that might be associated with elevated levels of ambient ozone in the Front Range.
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Wanty, Richard B., Andrew H. Manning, Michaela R. Johnson, and Philip L. Verplanck. "A 20-year record of water chemistry in an alpine setting, Mount Emmons, Colorado, USA." E3S Web of Conferences 98 (2019): 13002. http://dx.doi.org/10.1051/e3sconf/20199813002.
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From 1997 to the present, the U.S. Geological Survey and other agencies have been collecting water samples for chemical analyses on Mount Emmons in central Colorado, USA. The geology of Mount Emmons is dominated by Upper Cretaceous to Paleogene sediments of marine to continental origin, with felsic intrusive rocks interrupting the sedimentary block. Extensive sulphide-rich alteration accompanied the intrusive events and forms an alteration halo in the sediments. Weathering of these sulphide minerals has led to numerous springs and seeps with a naturally low pH and high concentrations of metals, especially Fe and Zn. Superimposed on the natural geochemical signature are acid, metal-rich drainages from several mines and drill holes. Thus, streams on Mt. Emmons have a mix of natural and anthropogenic metal sources. Nearly 450 samples compose the database, with numerous sample locations replicated from the late 1990s to the present. Although there does not appear to be any temporal pattern in the data, consistent spatial variations are observed that allow us to characterize the natural and anthropogenic water sources.
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Baldwin, Roger A., and Louis C. Bender. "Foods and nutritional components of diets of black bear in Rocky Mountain National Park, Colorado." Canadian Journal of Zoology 87, no. 11 (November 2009): 1000–1008. http://dx.doi.org/10.1139/z09-088.
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We used scat analysis to determine diets and relative nutritional values of diets for black bears ( Ursus americanus Pallas, 1780) in Rocky Mountain National Park, Colorado, from 2003 to 2006, and compared foods consumed and nutritional components to identify important sources of fecal gross energy (GE), crude fat (CF), and fecal nitrogen (FN) in annual and seasonal diets. Patterns of use of food classes followed typical seasonal patterns for bears, although use of animal matter was among the highest reported (>49% annually). Use of animal matter increased after spring, although crude protein levels in bear diets were always >25%. GE was typically lowest for grasses and other herbaceous plants and highest for ants and ungulates; FN was strongly positively related to most animal sources, but negatively correlated with vegetative matter; and CF showed the strongest positive relationship with ungulates and berries, with the latter likely influenced by the presence of seeds. Compared with historic data (1984–1991), contemporary diets included substantially greater prevalence of anthropogenic foods, which likely contributed to increases in size, condition, and productivity of the contemporary bear population. Management strategies are needed to increase quantity and quality of natural foods while minimizing dependence on anthropogenic sources.
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Lowry, Anthony R., and Robert B. Smith. "Flexural rigidity of the Basin and Range-Colorado Plateau-Rocky Mountain transition from coherence analysis of gravity and topography." Journal of Geophysical Research: Solid Earth 99, B10 (October 10, 1994): 20123–40. http://dx.doi.org/10.1029/94jb00960.
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