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Research about Arizona, California, Colorado, Nevada, New Mexico, Utah

Source-linked reports with geographic coverage including Arizona, California, Colorado, Nevada, New Mexico, Utah.

At least 19 recordsLinked to original sources
USGS2025

Rainfall thresholds for postfire debris-flow initiation vary with short-duration rainfall climatology

The size, frequency, and geographic scope of severe wildfires are expanding across the globe, including in the Western United States. Recently burned steeplands have an increased likelihood of debris flows, which pose hazards to downstream communities. The conditions for postfire debris-flow initiation are commonly expressed as rainfall intensity-duration thresholds, which can be estimated given sufficient observational history. However, the spread of wildfire across diverse climates poses a challenge for accurate threshold prediction in areas with limited observations. Studies of mass-movement processes in unburned areas indicate that thresholds vary with local climate, such that higher rainfall rates are required for initiation in climates characterized by frequent intense rainfall. Here, we use three independent methods to test whether initiation of postfire runoff-generated debris flows across the Western United States varies similarly with climate. Through the compilation of observed thresholds at various fires, analysis of the spatial density of observed debris flows, and quantification of feature importance at different spatial scales, we show that postfire debris-flow initiation thresholds vary systematically with short-duration rainfall-intensity climatology. The predictive power of climatological data sets that are readily available before a fire occurs offers a much-needed tool for hazard management in regions that are facing increased wildfire activity, have sparse observational history, and/or have limited resources for field-based hazard assessment. Furthermore, if the observed variation in thresholds reflects long-term adjustment of the landscape to local climate, rapid shifts in rainfall intensity related to climate change will likely induce spatially variable shifts in postfire debris-flow likelihood.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2020

The water-year water balance of the Colorado River Basin

Model‐estimated monthly water balance components (i.e., potential evapotranspiration, actual evapotranspiration, and runoff ( R )) for 146 United States (U.S.) Geological Survey 8‐digit hydrologic units located in the Colorado River Basin (CRB) are used to examine the temporal and spatial variability of the CRB water balance for water years 1901 through 2014 (a water year is the period from October 1 of one year through September 30 of the following year). Results indicate that the CRB can be divided into six subregions with similar temporal variability in monthly R . The water balance analyses indicated that approximately 75% of total water‐year R is generated by just one CRB subregion and that most of the R in the basin is derived from surplus ( S ) water generated during the months of October through April. Furthermore, the analyses show that temporal variability in S is largely controlled by the occurrence of negative atmospheric pressure anomalies over the northwestern conterminous U.S. (CONUS) and positive atmospheric pressure anomalies over the southeastern CONUS. This combination of atmospheric pressure anomalies results in an anomalous flow of moist air from the North Pacific Ocean into the CRB, particularly the Upper CRB. Additionally, the occurrence of extreme dry and wet periods in the CRB appears to be related to variability of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2020

Gaps and hotspots in the state of knowledge of pinyon-juniper communities

Pinyon-juniper (PJ) plant communities cover a large area across North America and provide critical habitat for wildlife, biodiversity and ecosystem functions, and rich cultural resources. These communities occur across a variety of environmental gradients, disturbance regimes, structural conditions and species compositions, including three species of juniper and two species of pinyon. PJ communities have experienced substantial changes in recent decades and identifying appropriate management strategies for these diverse communities is a growing challenge. Here, we surveyed the literature and compiled 441 studies to characterize patterns in research on PJ communities through time, across geographic space and climatic conditions, and among focal species. We evaluate the state of knowledge for three focal topics: 1) historical stand dynamics and responses to disturbance, 2) land management actions and their effects, and 3) potential future responses to changing climate. We identified large and potentially important gaps in our understanding of pinyon-juniper communities both geographically and topically. The effect of drought on Pinus edulis, the pinyon pine species in eastern PJ communities was frequently addressed, while few studies focused on drought effects on Pinus monophylla , which occurs in western PJ communities. The largest proportion of studies that examined land management actions only measured their effects for one year. Grazing was a common land-use across the geographic range of PJ communities yet was rarely studied. We found only 39 studies that had information on the impacts of anthropogenic climate change and most were concentrated on Pinus edulis . These results provide a synthetic perspective on PJ communities that can help natural resource managers identify relevant knowledge needed for decision-making and researchers design new studies to fill important knowledge gaps.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2020

The recurrence interval of post-fire debris-flow generating rainfall in the southwestern United States

In the southwestern United States, post-fire debris flows commonly initiate during short bursts of intense rainfall. To date, the frequency of the rainfall rates has not been quantified. Here, we combine an existing database of debris-flow occurrences and corresponding peak storm intensities with a geospatial library of rainfall recurrence interval (RI) information and climate type to determine the distribution of the estimated frequencies of the rainfall associated with 316 observed post-fire debris flows in the southwestern United States. Our results indicate that a majority (77%) of the observed debris flows were triggered by rainfall intensities with RI less than 2 years. Climatic and geographic differences in RI were evident in our analysis. Debris flows in most of the analyzed climates within California, Colorado, and New Mexico were primarily associated with 1-year or less RI intensities, whereas debris flows in arid portions of Arizona, Colorado, and Utah tended to be generated during storms greater than 2-year RI. Event consequence, as defined by the impact on downstream communities and infrastructure, was not directly related to RI, as very destructive debris flows were initiated at a wide range of RI intensities. Our results highlight that post-fire debris-flow initiation can be expected during common rainstorms in the southwestern United States, therefore emergency management plans and risk mitigation efforts must focus on both extreme and frequent rainstorms.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2017

Subsequent-year recaptures at winter sites in three species of shrubland sparrows (Emberizidae)

The tendency by individual birds to return to winter sites in subsequent years can be important in assessing the potential influence of habitat changes during the nonbreeding period. We recaptured five Brewer's ( Spizella breweri ), seven sagebrush ( Artemisiospiza nevadensis ), and three black-throated ( Amphispiza bilineata ) sparrows from 1–3 subsequent years at the same winter location following their initial capture. Two Brewer's and one sagebrush sparrow returned to the same winter location at least 4 years after their initial capture. Levels of feather deuterium indicated that birds captured together on winter sites had different breeding ranges. Although individuals of these species returned to specific sites used in previous years, the low recapture rate suggests that wintering individuals may use an itinerant strategy adapted to seasonal food resources.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2015

The quality of our Nation's waters: Water quality in basin-fill aquifers of the southwestern United States: Arizona, California, Colorado, Nevada, New Mexico, and Utah, 1993-2009

The Southwest Principal Aquifers consist of many basin-fill aquifers in California, Nevada, Utah, Arizona, New Mexico, and Colorado. Demands for irrigation and drinking water have substantially increased groundwater withdrawals and irrigation return flow to some of these aquifers. These changes have increased the movement of contaminants from geologic and human sources to depths used to supply drinking water in several basin-fill aquifers in the Southwest.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2013

The biogeographic histories of Pinus edulis and Pinus monophylla over the last 50,000 years

Well-preserved pine needles found in fossil packrat middens document the biogeographic responses of pinyon pines to changing climates over the last 50,000 years. During the full glacial Wisconsinan (MIS2), Pinus monophylla (single-needle pinyon), Pinus edulis (Colorado pinyon), and P. edulis var. fallax (Arizona singleleaf pinyon) all grew along the southern portions of their current ranges. P. monophylla extended from the southern Sierra Nevada across the Mojave Desert to northwestern Arizona. P. edulis grew from northwestern Arizona across central Arizona to New Mexico and south to westernmost Texas. P. edulis var. fallax grew throughout what is now the Sonoran Desert of southern Arizona. Application of the modern climate requirements for these species suggest that winter precipitation at this time was at least 150% of modern, but also that summer precipitation may have been somewhat greater than today, at least at the northernmost end of the Gulf of California. During the Bølling and Allerød intervals P. edulis and P. edulis var. fallax quickly expanded northward over the Mogollon Rim of central Arizona into the Little Colorado River basin and northwestern Arizona. This northerly expansion of the fallax variety during the Allerød interval suggests that temperatures were warmer than most of the latest Wisconsinan and that summer precipitation was at least 120% of modern. After the rapid warming at the start of the Holocene (11.7 ka), P. monophylla and P. edulis populations were reduced in extent as their retreating southerly stands were not immediately replaced by expansion into cooler regions. These populations slowly expanded 300–500 km northward at rates between 20 and 60 m y −1 , reaching some of their current northern limits only within the last millennium. Increases in temperature expected over the next several hundred years will result in a similar reduction in populations unless this warming is ameliorated by favorable increases in precipitation. The consistent needle anatomy and distributions of the three types relative to each other suggest that there has been little evolutionary change discernible from these needles over at least the last 25,000 years.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2013

Water resources in the desert southwest

As the old saying goes, there is nothing more precious than water in the desert. The Ancestral Puebloans, Hohokam, and other pre-Columbian cultures knew this and built their civilizations near guaranteed water supplies. When the Spaniards arrived in present-day Arizona, they found that the Tohono O’odham and Piman cultures had settled in prime riverine sites, turning perennial flow through lush riparian ecosystems into irrigation water for productive agriculture. The Spaniards followed suit, building their missions along perennial reaches of the Santa Cruz River, including at one place aptly named “Punta de Agua” (Point of Water) south of Tucson. When the Mormons spread southward from Utah in the 1870s, their destinations were riverside settings on the Little Colorado, Salt, and San Pedro Rivers (Figure 4.1).

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2013

Observed changes in phenology across the USA: A regional review for the 2013 National Climate Assessment, Southwest Regional Information Sheet

This is one in a series of eight, geographic region-focused information sheets that summarizes documented changes in plant and animal phenology over the past century across the United States. This summary is based on long-term studies (10 years or more) published in the primary scientific literature since 2001. A forthcoming manuscript synthesizes the findings of the eight regional information sheets. This information was developed in support of the U.S. Global Change Research Program’s National Climate Assessment and can be used to facilitate preparation for the cascading effects of ongoing climate change.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2012

Predicted nitrate and arsenic concentrations in basin-fill aquifers of the Southwestern United States

The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) is conducting a regional analysis of water quality in the principal aquifer systems across the United States. The Southwest Principal Aquifers (SWPA) study is building a better understanding of the susceptibility and vulnerability of basin-fill aquifers in the region to groundwater contamination by synthesizing baseline knowledge of groundwater-quality conditions in 16 basins previously studied by the NAWQA Program. The improved understanding of aquifer susceptibility and vulnerability to contamination is assisting in the development of tools that water managers can use to assess and protect the quality of groundwater resources. Human-health concerns and economic considerations associated with meeting drinking-water standards motivated a study of the vulnerability of basin-fill aquifers to nitrate con­tamination and arsenic enrichment in the southwestern United States. Statistical models were developed by using the random forest classifier algorithm to predict concentrations of nitrate and arsenic across a model grid that represents about 190,600 square miles of basin-fill aquifers in parts of Arizona, California, Colorado, Nevada, New Mexico, and Utah. The statistical models, referred to as classifiers, reflect natural and human-related factors that affect aquifer vulnerability to contamina­tion and relate nitrate and arsenic concentrations to explana­tory variables representing local- and basin-scale measures of source, aquifer susceptibility, and geochemical conditions. The classifiers were unbiased and fit the observed data well, and misclassifications were primarily due to statistical sampling error in the training datasets. The classifiers were designed to predict concentrations to be in one of six classes for nitrate, and one of seven classes for arsenic. Each classification scheme allowed for identification of areas with concentrations that were equal to or exceeding the U.S. Environmental Protection Agency drinking-water standard. Whereas 2.4 percent of the area underlain by basin-fill aquifers in the study area was predicted to equal or exceed this standard for nitrate (10 milligrams per liter as N; mg/L), 42.7 percent was predicted to equal or exceed the standard for arsenic (10 micrograms per liter; μg/L). Areas predicted to equal or exceed the drinking-water standard for nitrate include basins in central Arizona near Phoenix; the San Joaquin, Inland, and San Jacinto basins of California; and the San Luis Valley of Colorado. Much of the area predicted to equal or exceed the drinking-water standard for arsenic is within a belt of basins along the western portion of the Basin and Range Physiographic Province in Nevada, California, and Arizona. Predicted nitrate and arsenic concentrations are substantially lower than the drinking-water standards in much of the study area—about 93.0 percent of the area underlain by basin-fill aquifers was less than one-half the standard for nitrate (5.0 mg/L), and 50.2 percent was less than one-half the standard for arsenic (5.0 μg/L).

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2011

Effects of natural and human factors on groundwater quality of basin-fill aquifers in the southwestern United States: Conceptual models for selected contaminants

As part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program, the Southwest Principal Aquifers (SWPA) study is building a better understanding of the factors that affect water quality in basin-fill aquifers in the Southwestern United States. The SWPA study area includes four principal aquifers of the United States: the Basin and Range basin-fill aquifers in California, Nevada, Utah, and Arizona; the Rio Grande aquifer system in New Mexico and Colorado; and the California Coastal Basin and Central Valley aquifer systems in California. Similarities in the hydrogeology, land- and water-use practices, and water-quality issues for alluvial basins within the study area allow for regional analysis through synthesis of the baseline knowledge of groundwater-quality conditions in basins previously studied by the NAWQA Program. Resulting improvements in the understanding of the sources, movement, and fate of contaminants are assisting in the development of tools used to assess aquifer susceptibility and vulnerability. This report synthesizes previously published information about the groundwater systems and water quality of 15 information-rich basin-fill aquifers (SWPA case-study basins) into conceptual models of the primary natural and human factors commonly affecting groundwater quality with respect to selected contaminants, thereby helping to build a regional understanding of the susceptibility and vulnerability of basin-fill aquifers to those contaminants. Four relatively common contaminants (dissolved solids, nitrate, arsenic, and uranium) and two contaminant classes (volatile organic compounds (VOCs) and pesticide compounds) were investigated for sources and controls affecting their occurrence and distribution above specified levels of concern in groundwater of the case-study basins. Conceptual models of factors that are important to aquifer vulnerability with respect to those contaminants and contaminant classes were subsequently formed. The conceptual models are intended in part to provide a foundation for subsequent development of regional-scale statistical models that relate specific constituent concentrations or occurrence in groundwater to natural and human factors.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2010

Conceptual understanding and groundwater quality of selected basin-fill aquifers in the Southwestern United States

The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey has been conducting a regional analysis of water quality in the principal aquifer systems in the southwestern United States (hereinafter, “Southwest”) since 2005. Part of the NAWQA Program, the objective of the Southwest Principal Aquifers (SWPA) study is to develop a better understanding of water quality in basin-fill aquifers in the region by synthesizing information from case studies of 15 basins into a common set of important natural and human-related factors found to affect groundwater quality. The synthesis consists of three major components: 1. Summary of current knowledge about the groundwater systems, and the status of, changes in, and influential factors affecting quality of groundwater in basin-fill aquifers in 15 basins previously studied by NAWQA (this report). 2. Development of a conceptual model of the primary natural and human-related factors commonly affecting groundwater quality, thereby building a regional understanding of the susceptibility and vulnerability of basin-fill aquifers to contaminants. 3. Development of statistical models that relate the concentration or occurrence of specific chemical constituents in groundwater to natural and human-related factors linked to the susceptibility and vulnerability of basin-fill aquifers to contamination. Basin-fill aquifers occur in about 200,000 mi 2 of the 410,000 mi 2 SWPA study area and are the primary source of groundwater supply for cities and agricultural communities. Four of the principal aquifers or aquifer systems of the United States are included in the basin-fill aquifers of the study area: (1) the Basin and Range basin-fill aquifers in California, Nevada, Utah, and Arizona; (2) the Rio Grande aquifer system in New Mexico and Colorado; (3) the California Coastal Basin aquifers; and (4) the Central Valley aquifer system in California. Because of the generally limited availability of surface-water supplies in the arid to semiarid climate, cultural and economic activities in the Southwest are particularly dependent on supplies of good-quality groundwater. Irrigation and public-supply withdrawals from basin-fill aquifers in the study area account for about one quarter of the total withdrawals from all aquifers in the United States. Many factors influence the quality of groundwater in the 15 case-study basins, but some common factors emerge from the basin summaries presented in this report. These factors include the chemical composition of the recharge water, consolidated rock geology and composition of aquifer materials derived from consolidated rock, and land and water use. The major water-quality issues in many of the developed case-study basins are increased concentrations of dissolved solids, nitrate, and VOCs in groundwater as a result of human activities. The information presented and the citations listed in this report serve as a resource for those interested in the groundwater-flow systems in the NAWQA case-study basins. The summaries of water-development history, hydrogeology, conceptual understanding of the groundwater system under both predevelopment and modern conditions, and effects of natural and human-related factors on groundwater quality presented in the sections on each basin also serve as a foundation for the synthesis and modeling phases of the SWPA regional study.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2009

Geospatial data to support analysis of water-quality conditions in basin-fill aquifers in the southwestern United States

The Southwest Principal Aquifers study area consists of most of California and Nevada and parts of Utah, Arizona, New Mexico, and Colorado; it is about 409,000 square miles. The Basin-fill aquifers extend through about 201,000 square miles of the study area and are the primary source of water for cities and agricultural communities in basins in the arid and semiarid southwestern United States (Southwest). The demand on limited ground-water resources in areas in the southwestern United States has increased significantly. This increased demand underscores the importance of understanding factors that affect the water quality in basin-fill aquifers in the region, which are being studied through the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program. As a part of this study, spatial datasets of natural and anthropogenic factors that may affect ground-water quality of the basin-fill aquifers in the southwestern United States were developed. These data include physical characteristics of the region, such as geology, elevation, and precipitation, as well as anthropogenic factors, including population, land use, and water use. Spatial statistics for the alluvial basins in the Southwest have been calculated using the datasets. This information provides a foundation for the development of conceptual and statistical models that relate natural and anthropogenic factors to ground-water quality across the Southwest. A geographic information system (GIS) was used to determine and illustrate the spatial distribution of these basin-fill variables across the region. One hundred-meter resolution raster data layers that represent the spatial characteristics of the basins' boundaries, drainage areas, population densities, land use, and water use were developed for the entire Southwest.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2002

Early to Middle Proterozoic construction of the Mojave province, southwestern United States

Zircon and monazite U-Pb geochronology of rocks in the western Mojave province of the southwest US reveals that the Proterozoic arc exposed there shares an intrusive and deformational history with rocks exposed further east in the Yavapai and Mazatzal belts after approximately 1780 Ma. Consequently, it seems likely that the Mojave province was contiguous with these other Laurentian provinces by that time. Isotopic and geochronologic data also suggest that Mojave province plutonic rocks inherit their distinctive isotopic compositions, at least in part, from an enriched lithospheric mantle source and interaction with sedimentary rocks containing Archean detritus.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS1967

Devonian of the Southwestern United States

The structural framework that controlled Devonian deposition consisted of, from west to east: (1) a eugeosynclinal area in northern California and western Nevada; (2) a miogeosynclinal area in southeastern California, eastern Nevada, and western Utah; and (3) a cratonic area in Arizona, eastern Utah, Colorado, New Mexico, and western Texas, east of a northeast-trending hinge line (Wasatch line). The eugeosyncline contains a fragmentary record of Middle Devonian rocks at least 4,000 feet thick characterized by thin-bedded chert, siliceous mudstone, and some limestone and volcanic rocks. The original thickness, however, probably exceeded 6,000 feet and probably included Lower and Upper Devonian rocks. The miogeosyncline contains Lower, Middle, and Upper Devonian rocks as much as 6,000 feet thick characterized by thick units of dolomite and limestone and some local interbeds of sandstone. A transitional zone perhaps 50 miles wide separates the eugeosynclinal and miogeosynclinal facies. The craton contains mostly Upper Devonian rocks, generally less than 1,000 feet thick, characterized by dolomite and limestone and local interbeds of sandstone and mudstone. Widespread crustal movements occurred during Late Devonian time. The Antler orogeny in Nevada initiated a culm facies in the geosyncline. Eugeosynclinal and transitional rocks including those of Devonian age were uplifted to form the Antler orogenic belt, and then were thrust eastward over autochthonous miogeosynclinal rocks in latest Devonian or earliest Mississippian time. Folding and faulting, and subsequent erosion on local uplifts, produced clastic deposits of Late Devonian age in Utah and southwestern Colorado. Devonian rocks in many parts of the geosynclinal area have been moved since Devonian time by large-scale, generally eastward thrusting, oroflexural bending and strike-slip faulting. Four major subdivisions of the Devonian System and related rocks are treated separately: 1) Lower Devonian (Gedinnian, Siegenian, Emsian) and related Upper Silurian (Ludlovian) rocks. 2) Middle Devonian (Eifelian and Givetian) rocks. 3) Lower Upper Devonian (Frasnian, to I ) rocks. 4) Upper Upper Devonian (Famennian, to II-VI ) and related lowermost Mississippian (Tournaisian, cu I ) rocks.

Conference Paper↗