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USGS2008

A Regional Approach to Wildlife Monitoring Related to Energy Exploration and Development in Colorado

The U.S. Bureau of Land Management (BLM) is currently developing a National Monitoring Strategy that will guide efforts to create an efficient and effective process for monitoring land health by BLM. To inform the ongoing development of the national strategy, BLM selected two States (Colorado, Alaska) to serve as focal areas on which to base a flexible framework for developing monitoring programs that evaluate wildlife responses to energy development. We developed a three-phase monitoring plan to serve as a template and applied it to the design of a monitoring program for the Colorado focal area (White River and Glenwood Springs Field Offices of the BLM). Phase I is a synthesis and assessment of current conditions that capitalizes on existing but under used data sources. A key component is the use of existing habitat and landscape models to evaluate the cumulative effects of surface disturbance. Phase II is the data collection process that uses information provided in Phase I to refine management objectives and provide a linkage to management decisions. The linkage is established through targeted monitoring, adaptive management, and research. Phase III establishes priorities and strategies for regional and national monitoring, and facilitates coordination among other land management agencies and organizations. The three phases are designed to be flexible and complementary. The monitoring plan guides an iterative process that is performed incrementally, beginning with the highest-priority species and management issues, while building on lessons learned and coordination among administrative levels. The activities associated with each phase can be repeated or updated as new information, data, or tools become available. This allows the development of a monitoring program that expands gradually and allows for rapid implementation. A demonstration application of the three-phase monitoring plan was conducted for a study area encompassing five BLM field offices in Colorado: White River, Glenwood Springs, Kremmling, Grand Junction, and Little Snake. The overall study area was selected to encompass the primary distribution of sagebrush and greater sage-grouse (Centrocercus urophasianus) in Colorado and to provide a larger context for evaluating priority management issues of the White River and Glenwood Springs Field Offices. Within the study area, we selected an additional scale of analysis: the Roan Plateau, an area of increased energy development. We focused our demonstration project on the primary objectives identified by the BLM and other stakeholders: (1) How do we evaluate the cumulative effects of energy development and mitigation activities on species of management interest or concern? (2) How can cumulative effects, including direct and indirect effects, be quantified relative to natural variation? (3) How can we implement compliance and effectiveness monitoring to determine whether lease stipulations are met and restoration/mitigation goals are achieved? We targeted greater sage-grouse because this species was identified as a monitoring priority for the White River Field Office. We also evaluated landscape-level indices to address fragmentation resulting from surface disturbance. The primary purpose of this exercise was to highlight the types of analyses and approaches that could be used to evaluate energy development in an application of the three-phase framework. We provide examples of Phase I products that can be used to guide the refinement of management objectives, development of adaptive management and research frameworks, and planning activities in Phase II. Finally, we report on the BLM's National Sage-Grouse Habitat Conservation Strategy as an example of Phase III activities. The development of an effective monitoring program is a daunting task, and will be difficult to implement by the BLM independently due to the current work load of staff. However, the scientific expertise and experience for developing cr

Open-File Report↗

USGS1943

Geology of the Cimarron Range, New Mexico

In north-central New Mexico the rugged Cimarron Range marks the eastern margin of the Southern Rocky Mountains, abruptly rising more than 5000 feet above the adjacent Great Plains. Structurally the range is a northward-plunging anticline with a core of pre-Cambrian crystalline rocks. Faulting along the eastern and western margins of the anticline separates the mountains from the Great Plains and the Moreno Valley. North of Cimarron Canyon the anticline plunges beneath the Tertiary sediments of the Raton Coal Basin. To the south the structure is obscured by the basaltic flows of the Ocaté Mesa. Upturned Paleozoic to Tertiary sedimentary rocks crop out along the eastern and northern margin of the anticlinal uplift. Regional relations are obscured by extensive Tertiary intrusions in the northern portion of the area and by the lava flows to the south. In the valley of Rayado Creek a volcanic plug which fed some of the lava flows has been exposed by erosion. In this region there is evidence for a Mid-Tertiary surface of low relief in the central portion of the mountains, a later lava-capped surface believed to be the equivalent of the Broad Valley Stage, the surface of the Park Plateau, and the Ocate Mesa. Three well-developed gravel-capped Pleistocene pediment surfaces extend steplike from the mountain front into the Great Plains. Both structurally and topographically the Cimarron Range is similar to the Colorado Front Range. An attempt is made to reconstruct the geologic history of the Cimarron Range and to fit it into the broader story of the development of the Southern Rocky Mountains in New Mexico. © 1943 Geological Society of America.

New Mexico↗

USGS2006

Fossils from the Middle Jurassic Wanakah formation near Delta in western Colorado

The Middle Jurassic Wanakah Formation averages about 30 m in thickness in Colorado. Fossils are sparse and include fish, ostracodes, and trace fossils. A thin (0.03-0.45 m) fossil bed near the middle of the formation extends for some 48 km along the northeast flank of the Uncompahgre Plateau near Delta. The fossil bed at one locality contains one pelecypod identified possibly as Modiolus cf. M. subimbricatus (Meek), as well as other specimens too poorly preserved for identification. Previously, Mytilus was found in the same fossil bed at another locality by C.N. Holmes. The Wanakah Formation is primarily of terrestrial origin, but the fossil bed represents a shallow-marine incursion.

Scientific Investigations Report↗

USGS1988

Hydrologic analysis of the Rio Grande basin north of Embudo, New Mexico, Colorado and New Mexico

Water yield was estimated for each of the five regions that represent contrasting hydrologic regimes in the 10,400 square miles of the Rio Grande basin above Embudo, New Mexico. Water yield was estimated as 2,800 cubic feet per second for the San Juan Mountains, and 28 cubic feet per second for the Taos Plateau. Evapotranspiration exceeded precipitation by 150 cubic feet per second on the Costilla Plains and 2,400 cubic feet per second on the Alamosa Basin. A three-dimensional model was constructed to represent the aquifer system in the Alamosa Basin. A preliminary analysis concluded that: (1) a seven-layer model representing 3,200 feet of saturated thickness could accurately simulate the behavior of the flow equation; and (2) the 1950 condition was approximately stable and would be a satisfactory initial condition. Reasonable modifications to groundwater withdrawals simulated 1950-79 water-level declines close to measured value. Sensitivity tests indicated that evapotranspiration salvage was the major source, 69 to 82 percent, of groundwater withdrawals. Evapotranspiration salvage was projected to be the source of most withdrawals.

Colorado, New Mexico↗

USGS1966

Volcanism in the western San Juan Mountains, Colorado

Three major cycles of volcanism during the Miocene and Pliocene formed a layered succession of calc-alkaline eruptive materials in the western San Juan Mountains nearly 1.5 miles thick and having a volume greater than 1,000 cubic miles. Each cycle was characterised by major eruptions followed by subsidence in the vent areas, and the resulting structure was a great volcanic plateau surrounding a complex of nested cauldrons. In the first cycle, cruption of several hundred cubic miles of tuff breccia and subordinate lavas was followed by subsidence that created the San Juan volcanic depression, about 15 miles wide and 30 miles long. During the second cycle, pyroclastic rocks and lava flows accumulated within this depression and on its borders, and the depression subsided further. During the third cycle, ash flows spead widely from centres within the depression, and their eruption resulted in formation and subsidence of the nearly circular comagmatic Silverton and Lake City cauldrons, each about 10 miles across, within the earlier depression. Cauldron subsidence in the second and third cycles was followed by resurgence and doming of the central blocks. Keystone grabens formed along the distended crests of the domed floors; graben faults formed in the third cycle were in part controlled by those formed in the second cycle. The distribution of post-cauldron radial and concentric fractures, dikes, and intrusive plutons, particularly around the Silverton cauldron, suggests that the underlying magma chamber must have been appreciably larger than the associated cauldrons.

Colorado↗

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↗

USGS1984

Water resources and potential hydrologic effects of oil-shale development in the southeastern Uinta Basin, Utah and Colorado

Proposed oil-shale mining in northeastern Utah is expected to impact the water resources of a 3,000-square-mile area. This report summarizes a comprehensive hydrologic investigation of the area which resulted in 13 published reports. Hydrologic information obtained during 1974-80 was used to evaluate the availability of water and to evaluate potential impacts of an oil-shale industry on the water resources. The study area is the southeastern part of the Uinta Basin, Utah and Colorado, where the hydrology is extremely variable. The normal annual precipitation averages 11 inches and varies with altitude. It ranges from less than 8 inches at altitudes below 5,000 feet along the White and Green Rivers to more than 20 inches where altitudes exceed 9,000 feet on the Roan Plateau. The White and Green Rivers are large streams that flow through the area. They convey an average flow of 4.3 million acre-feet per year from outside drainage areas of about 34,000 square miles, which is more than 150 times as much flow as that originating within the area. Streams originating in areas where precipitation is less than 10 inches are ephemeral. Mean annual runoff from the study area is about 28,000 acre-feet and ranges from less than 0.1 to 1.6 inches, depending on the location. At any given site, runoff varies greatly-from year to year and season to season. Potential evapotranspiration is large, exceeding precipitation in all years. Three major aquifers occur in the area. They are alluvial deposits of small areal extent along the major stream valleys; the bird's-nest aquifer of the Parachute Creek Member of the Green River Formation, which is limited to the central part of the study area; and the Douglas Creek aquifer of the Douglas Creek Member of the Green River Formation, which underlies most of the area. Total recoverable water in storage in the three aquifers is about 18 million acre-feet. Yields of individual wells and interference between wells limit the maximum practical withdrawal to about 20,000 acre-feet per year. An oil-shale industry in the southeastern Uinta Basin with a peak production of 400,000 barrels of oil per day would require a water supply of about 70,000 acre-feet per year. Sources of water supply considered for such an industry were: diversion from the natural flow of the White River, a proposed reservoir on the White River, diversion from the White River combined with proposed off-stream storage in Hells Hole Canyon, diversion from the Green River, and conjunctive use of ground and surface water. The proposed reservoir on the White River would trap about 90 percent of the sediment moving in the river and in turn would release almost sediment-free water. Possible impacts are changes in channel gradient in the downstream 18 miles of the White River and changes in bank stability. In some parts of the area, annual sheet-erosion rates are as great as 2.2 acre-feet per square mile but sediment yield to the White River is less than might be expected because the runoff is small. If process water from retort operations or water used in the construction of surface facilities is discharged into a normally dry streambed, increased channel erosion and sediment in tributary streams could result in increased sediment loads in the White River. In addition, sediment yields from retorted-shale piles with minimum slopes could exceed 0.1 acrefoot per square mile during a common storm. Thus, without safeguards, the useful life of any proposed reservoir or holding pond could be decreased considerably. Leachate water from retorted-shale piles has large concentrations of sodium and sulfate, and the chemical composition of retort waters differs considerably from that of the natural waters of the area. The retort waters contain a greater concentration of dissolved solids and more organic carbon and nutrients. Without proper disposal or impoundment of retort and leachate waters, the salinity of downstream waters in the Colorado River Basin would be increased.

Colorado, Utah↗

USGS2014

Geologic map of the Ute Mountain 7.5' quadrangle, Taos County, New Mexico, and Conejos and Costilla Counties, Colorado

The Ute Mountain 7.5' quadrangle is located in the south-central part of the San Luis Basin of northern New Mexico, in the Rio Grande del Norte National Monument, and contains deposits that record volcanic, tectonic, and associated alluvial and colluvial processes over the past four million years. Ute Mountain has the distinction of being one of the largest intermediate composition eruptive centers of the Taos Plateau, a largely volcanic tableland occupying the southern portion of the San Luis Basin. Ute Mountain rises to an elevation in excess of 3,000 m, nearly 700 m above the basaltic plateau at its base, and is characterized by three distinct phases of Pliocene eruptive activity recorded in the stratigraphy exposed on the flanks of the mountain and in the Rio Grande gorge. Unconformably overlain by largely flat-lying lava flows of Servilleta Basalt, the area surrounding Ute Mountain records a westward thickening of basin-fill volcanic deposits interstratified in the subsurface with Pliocene basin-fill sedimentary deposits derived from older Tertiary and Precambrian sources to the east. Superimposed on this volcanic stratigraphy are alluvial and colluvial deposits derived from the flanks of Ute Mountain and more distally-derived alluvium from the uplifted Sangre de Cristo Mountains to the east, that record a complex temporal and stratigraphic succession of Quaternary basin deposition and erosion. Pliocene and younger basin deposition was accommodated along predominantly north-trending fault-bounded grabens. These poorly exposed fault scarps cutting lava flows of Ute Mountain volcano. The Servilleta Basalt and younger surficial deposits record largely down-to-east basinward displacement. Faults are identified with varying confidence levels in the map area. Recognizing and mapping faults developed near the surface in young, brittle volcanic rocks is difficult because: (1) they tend to form fractured zones tens of meters wide rather than discrete fault planes, (2) the relative youth of the deposits has resulted in only modest displacements on most faults, and (3) some of the faults may have significant strike-slip components that do not result in large vertical offsets that are readily apparent in offset of sub-horizontal contacts. Those faults characterized as “certain” either have distinct offset of map units or had slip planes that were directly observed in the field. Lineaments defined from magnetic anomalies form an additional constraint on potential fault locations and are indicated as such on the map sheet.

Colorado, New Mexico↗

USGS2006

Spatial data for Eurycea salamander habitats associated With three aquifers in south-central Texas

Eurycea salamander taxa comprise 12 known species that inhabit springs and caves in south-central Texas. Many of these are threatened or endangered species, and some are found only at one location. A number of the neotenic salamanders might be at risk from habitat loss associated with declines in ground-water levels. Eurycea salamander habitats are associated with three aquifers in south-central Texas: (1) the Edwards-Trinity (Plateau) aquifer, (2) the Edwards (Balcones Fault Zone) aquifer, and (3) the Trinity aquifer. The Edwards (Balcones fault zone) aquifer is commonly separated into three segments: from southwest to northeast, the San Antonio segment, the Barton Springs segment, and the northern segment. The Trinity aquifer south of the Colorado River can be divided into three permeable zones, the upper, middle, and lower zone. The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, developed this report (geodatabase) to aggregate the spatial data necessary to assess the potential effects of ground-water declines on known Eurycea habitat locations in south-central Texas. The geodatabase provides information about spring habitats, spring flow, cave habitats, aquifers, and projected water levels.

Data Series↗

USGS2016

Geomorphic evolution of the San Luis Basin and Rio Grande in southern Colorado and northern New Mexico

The San Luis Basin encompasses the largest structural and hydrologic basin of the Rio Grande rift. On this field trip, we will examine the timing of transition of the San Luis Basin from hydrologically closed, aggrading subbasins to a continuous fluvial system that eroded the basin, formed the Rio Grande gorge, and ultimately, integrated the Rio Grande from Colorado to the Gulf of Mexico. Waning Pleistocene neotectonic activity and onset of major glacial episodes, in particular Marine Isotope Stages 11–2 (~420–14 ka), induced basin fill, spillover, and erosion of the southern San Luis Basin. The combined use of new geologic mapping, fluvial geomorphology, reinterpreted surficial geology of the Taos Plateau, pedogenic relative dating studies, 3 He surface exposure dating of basalts, and U-series dating of pedogenic carbonate supports a sequence of events wherein pluvial Lake Alamosa in the northern San Luis Basin overflowed, and began to drain to the south across the closed Sunshine Valley–Costilla Plain region ≤400 ka. By ~200 ka, erosion had cut through topographic highs at Ute Mountain and the Red River fault zone, and began deep-canyon incision across the southern San Luis Basin. Previous studies indicate that prior to 200 ka, the present Rio Grande terminated into a large bolson complex in the vicinity of El Paso, Texas, and systematic, headward erosional processes had subtly integrated discontinuously connected basins along the eastern flank of the Rio Grande rift and southern Rocky Mountains. We propose that the integration of the entire San Luis Basin into the Rio Grande drainage system (~400–200 ka) was the critical event in the formation of the modern Rio Grande, integrating hinterland basins of the Rio Grande rift from El Paso, Texas, north to the San Luis Basin with the Gulf of Mexico. This event dramatically affected basins southeast of El Paso, Texas, across the Chisos Mountains and southeastern Basin and Range province, including the Rio Conchos watershed and much of the Chihuahuan Desert, inducing broad regional landscape incision and exhumation.

Colorado, New Mexico↗

USGS2026

Peak-, mean-, and low-streamflow regional-regression equations for natural streamflow in central and western Colorado, 2019

The U.S. Geological Survey (USGS), in cooperation with the Colorado Department of Transportation, developed peak-, mean-, and low-streamflow regional-regression equations for estimating various statistics for natural streamflow in hydrologic regions of central and western Colorado. The peak-streamflow regression equations were developed using data from 418 streamgages, consisting of 15,202 years of record and a mean of approximately 36 years of record per streamgage. The mean- and low-streamflow regional-regression equations were developed using data from 323 streamgages where daily streamflow data were collected year-round. The annual exceedance-probability discharges for each streamgage were computed using the USGS software program PeakFQ. Mean monthly and 7-day minimum and maximum streamflows were computed using the USGS software program SWToolbox. Streamflow-duration values were computed using an R script. The regional-regression equations were determined using data for the period of record for a given streamgage through water year 2019. Geographic information systems datasets were used to develop 55 basin and 42 climatic characteristics, which were evaluated as candidate explanatory variables in the regression analysis. For the peak-streamflow regional-regression equations, the study area was divided into four hydrologic regions based on mean basin elevation, including the Plateau (less than 8,014 feet), Mid-Elevation (8,015 feet to 9,492 feet), Sub-Alpine (9,493 feet to 10,490 feet), and Alpine (greater than 10,490 feet) regions. For the peak-streamflow equations, the selection of basin and climatic characteristics was based on the 1-percent annual exceedance-probability discharge for each hydrologic region. For the mean streamflow, streamflow-duration values, and 7-day minimum and maximum streamflows, the study area was divided into four hydrologic regions based on river basin, including the (1) Colorado-East Slope Headwaters, (2) Green River, (3) Rio Grande, and (4) San Juan-Dolores. For mean streamflows, basin and climatic characteristics were evaluated separately for the annual period and each month for each hydrologic region. Regional regression equations published in this report are available for use in the USGS web-based program StreamStats.

Colorado↗

USGS1981

Preliminary hydrologic evaluation of the North Horn Mountain coal-resource area, Utah

North Horn Mountain is part of a deeply dissected plateau in central Utah which is characterized by deep, narrow, steep-walled canyons with local relief of more than 1,000 feet. Geologic units exposed in the North Horn Mountain area range in age from Late Cretaceous to Holocene and contain two mineable seams of Cretaceous coal. The area is in the drainage basin of the San Rafael River, in the Colorado River Basin. Runoff from the mountain is ephemeral. This runoff to the San Rafael River is by way of Cottonwood and Perron Creeks and represents less than 10 percent of their average annual runoff. Probable peak discharges (100-year flood) for the ephemeral streams draining North Horn Mountain are estimated to range from 200 to 380 cubic feet per second. The chemical quality of surface water in the area is good. The water is generally of a calcium magnesium bicarbonate type with average dissolved solids less than 500 milligrams per liter. Annual sediment yield in most of the area ranges from 0.1 to 0.2 acre-foot per square mile but locally is as high as 1.0 acre-foot per square mile. Most of the sediment is eroded during cloudbursts. Most of the ground water above the coal on North Horn Mountain probably is in perched aquifers. These aquifers support the flow of small seeps and springs. In some areas, the regional water table appears to extend upward into the coal. The principal source of recharge is precipitation that probably moves to aquifers along faults, joints, or fractures. This movement is apparently quite rapid. The dissolved-solids concentrations of ground water in the North Horn Mountain area range from less than 500 to about 1,000 milligrams per liter. Coal mining on North Horn Mountain should have minor "effects on the quantity and quality of surface water. The maximum predicted decrease in the annual flow of Ferron and Cottonwood Creeks is less than U percent. The sediment loads of affected streams could be significantly increased if construction were to take place during the summer cloudburst season. Subsidence, which usually follows underground coal mining, could create rock fractures through which a perched aquifer might be drained, thus depleting the flow of seeps or springs fed by that aquifer. It is considered unlikely that the mining will adversely affect the chemical quality of the ground water.

Utah↗

USGS1999

Physiographic rim of the Grand Canyon, Arizona: A digital database

This Open-File report is a digital physiographic map database. This pamphlet serves to introduce and describe the digital data. There is no paper map included in the Open-File report. The report does include, however, PostScript and PDF format plot files, each containing an image of the map. For those interested in a paper plot of information contained in the database or in obtaining the PostScript plot files, please see the section entitled "For Those Who Don't Use Digital Geologic Map Databases" below. This physiographic map of the Grand Canyon is modified from previous versions by Billingsley and Hendricks (1989), and Billingsley and others (1997). The boundary is drawn approximately along the topographic rim of the Grand Canyon and its tributary canyons between Lees Ferry and Lake Mead (shown in red). Several isolated small mesas, buttes, and plateaus are within this area, which overall encompasses about 2,600 square miles. The Grand Canyon lies within the southwestern part of the Colorado Plateaus of northern Arizona between Lees Ferry, Colorado River Mile 0, and Lake Mead, Colorado River Mile 277. The Colorado River is the corridor for raft trips through the Grand Canyon. Limestone rocks of the Kaibab Formation form most of the north and south rims of the Grand Canyon, and a few volcanic rocks form the north rim of parts of the Uinkaret and Shivwits Plateaus. Limestones of the Redwall Limestone and lower Supai Group form the rim of the Hualapai Plateau area, and Limestones of Devonian and Cambrian age form the boundary rim near the mouth of Grand Canyon at the Lake Mead. The natural physiographic boundary of the Grand Canyon is roughly the area a visitor would first view any part of the Grand Canyon and its tributaries.

Arizona↗

USGS1988

High-resolution 40Ar 39Ar chronology of Oligocene volcanic rocks, San Juan Mountains, Colorado

The central San Juan caldera complex consists of seven calderas from which eight major ash-flow tuffs were erupted during a period of intense volcanic activity that lasted for approximately 2 m.y. about 26–28 Ma. The analytical precision of conventional K-Ar dating in this time interval is not sufficient to unambiguously resolve this complex history. However, 40 Ar 39 Ar "> 40 Ar 39 Ar incremental-heating experiments provide data for a high-resolution chronology that is consistent with stratigraphie relations. Weighted-mean age-spectrum plateau ages of biotite and sanidine are the most precise with standard deviations ranging from 0.08 to 0.21 m.y. The pooled estimate of standard deviation for the plateau ages of 12 minerals is about 0.5 percent or about 125,000 to 135,000 years. Age measurements on coexisting minerals from one tuff and on two samples of each of two other tuffs indicate that a precision in the age of a tuff of better than 100,000 years can be achieved at 27 Ma. New data indicate that the San Luis caldera is the youngest caldera in the central complex, not the Creede caldera as previously thought.

Geochimica et Cosmochimica Acta↗

USGS2012

Wyoming Basin Ecoregion: Chapter 25 in Status and trends of land change in the Western United States--1973 to 2000

The Wyoming Basin Ecoregion (Omernik 1987; U.S. Environmental Protection Agency, 1999) covers approximately 128,914 km 2 (49,774 mi 2 ) in Wyoming and parts of northwestern Colorado, northeastern Utah, southeastern Idaho, and southern Montana (fig. 1). The ecoregion is bounded on the east by the Northwestern Great Plains Ecoregion; on the south and east by the Southern Rockies Ecoregion; on the south by the Colorado Plateaus Ecoregion; on the south and west by the Wasatch and Uinta Mountains Ecoregion; and on the north by the Middle Rockies Ecoregion and parts of the Montana Valley and Foothill Prairies Ecoregion (fig. 1). The ecoregion generally consists of broad intermountain basins dominated by arid grasslands and shrublands, as well as isolated hills and low mountains that merge to the south into a dissected plateau.

Colorado;Idaho;Montana;Utah;Wyoming↗

USGS2016

Variability in rainfall at monitoring stations and derivation of a long-term rainfall intensity record in the Grand Canyon Region, Arizona, USA

In this study, we examine rainfall datasets of varying temporal length, resolution, and spatial distribution to characterize rainfall depth, intensity, and seasonality for monitoring stations along the Colorado River within Marble and Grand Canyons. We identify maximum separation distances between stations at which rainfall measurements might be most useful for inferring rainfall characteristics at other locations. We demonstrate a method for applying relations between daily rainfall depth and intensity, from short-term high-resolution data to lower-resolution longer-term data, to synthesize a long-term record of daily rainfall intensity from 1950–2012. We consider the implications of our spatio-temporal characterization of rainfall for understanding local landscape change in sedimentary deposits and archaeological sites, and for better characterizing past and present rainfall and its potential role in overland flow erosion within the canyons. We find that rainfall measured at stations within the river corridor is spatially correlated at separation distances of tens of kilometers, and is not correlated at the large elevation differences that separate stations along the Colorado River from stations above the canyon rim. These results provide guidance for reasonable separation distances at which rainfall measurements at stations within the Grand Canyon region might be used to infer rainfall at other nearby locations along the river. Like other rugged landscapes, spatial variability between rainfall measured at monitoring stations appears to be influenced by canyon and rim physiography and elevation, with preliminary results suggesting the highest elevation landform in the region, the Kaibab Plateau, may function as an important orographic influence. Stations at specific locations within the canyons and along the river, such as in southern (lower) Marble Canyon and eastern (upper) Grand Canyon, appear to have strong potential to receive high-intensity rainfall that can generate runoff which may erode alluvium. The characterization of past and present rainfall variability in this study will be useful for future studies that evaluate more spatially continuous datasets in order to better understand the rainfall dynamics within this, and potentially other, deep canyons.

Arizona↗

USGS1952

Glaciation and drainage changes in the fish Lake Plateau, Utah

The Fish Lake Plateau , nearly centrally located among the High Plateaus of Utah , exhibits glacial and other geomorphic features of regional significance. The plateau is divided into two areas by Fish Lake and the wide valley of Sevenmile Creek. The Fish Lake trough is a structural basin; Sevenmile Valley may be largely erosional. Volcanic rocks of Tertiary age underlie most of the plateau ; early Tertiary sedimentary rocks are also present. Glaciated canyons with well-developed cirques are especially prominent along the east-facing sides of the Fish Lake trough and Sevenmile Valley. Ice-eroded features occur over much of the plateau top. Near the mouths of several of the glaciated canyons are two conspicuous sets of moraines. The older set is more extensive and less rugged than the younger and occurs at somewhat lower elevations. Two substages of glaciation thus recognized are correlated with Wisconsin I and II of Ray; probable correlatives of Wisconsin III, IV, and V are represented by moraines which are younger than these two sets. Fish Lake drains north into Fremont River, a tributary of the Colorado River. An abandoned southern outlet and waterfall, the latter at a higher elevation than the present elevation of the original northern bedrock divide, indicate drainage reversal. Evidence is presented which suggests that this reversal was pre-glacial and probably the result of fault-block tilting.

Utah↗

USGS2018

Fish Lake limnology and watershed aqueous geochemistry, Fish Lake Plateau, Utah

Fish Lake is located at 2696 m elevation on the Fish Lake Plateau with a bedrock geology of Oligocene to Pliocene age volcanics and Cretaceous to Eocene age sedimentary rocks. Lake bathymetry indicates a maximum depth of ~27 m and volume of 2.31 x 108 m3. The lake is dimictic with summer water column temperature declines of 13˚C between 7 to 15 m depth, whereas in spring and fall water column is isothermal. Numerous surface streams flow into the lake and there is one surface outflow stream, Lake Creek, which drains to the northeast into Johnson Valley Reservoir and the Fremont River, which is a tributary of the upper Colorado River. Surface inflow streams and spring waters are generally dilute and ionic compositions are consistent with bedrock geology. Spring and creek water oxygen and hydrogen stable isotope compositions indicate snowmelt is the predominant water source to the lake. High evaporative enrichment is indicated by lake water stable oxygen and hydrogen compositions and conservative ions, which suggest evaporative water loss equal or greater than inflow. The ionic and isotope data combined with preliminary discharge measurements provide a preliminary estimated lake-water residence time between approximately 15 and 30 years, although groundwater flux is currently unknown. Dissolved silica concentrations decline by two orders of magnitude between inflowing waters and summer lake waters, indicating substantial uptake by freshwater diatoms and high biological productivity. During summer, epilimnion pH values of 8.7 contribute to slight oversaturation with respect to calcite/aragonite, which suggests that precipitates could form in minor concentration. Below the thermocline pH is near neutral and carbonate mineral dissolution within the water column is likely.

Utah↗