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USGS2026

Small earthquake moment magnitude and implications for frequency–magnitude scaling of injection induced earthquakes of the Raton Basin

Accurate estimation of earthquake source parameters—such as moment magnitudes, corner frequencies, and stress drops—is essential for improving seismic hazard assessments and understanding earthquake physics. In this study, moment magnitudes ( M W ) are calculated for 31,581 earthquakes associated with wastewater injection in the Raton Basin (located along the border between northern New Mexico and southern Colorado) between 2016 and 2024 using radiative transfer theory to fit coda decay envelopes. Our results show that it is feasible to estimate moment magnitudes down to M W ~1 with coda envelopes from a small local monitoring network. Significant differences were found between M W and local magnitudes ( M L ) for small earthquakes ( M < 3.0). A linear relationship was optimized to convert M L to M W : M W = 0.7 M L + 0.96 and M W = 0.73 M L + 0.99 (for the events reported by the U.S. Geological Survey), which can be applied in future studies of Raton Basin seismicity. We find that b -values calculated employing different methods and using M L are approximately 1.0, while those using M W range from 1.2 to 1.4. A larger estimate of the b -value could influence interpretations of the statistical behavior of earthquakes associated with injection and consequently seismic hazard assessments based on a magnitude–frequency distribution. The potential differences between local versus moment magnitude-based earthquake statistics should be considered in other seismically active regions.

Colorado, New Mexico↗

USGS2024

Low flows from drought and water use reduced total dissolved solids fluxes in the Lower Colorado River Basin between 1976 to 2008

Study area: We evaluated the Virgin, Verde, Salt, and Gila Rivers in the Lower Colorado River Basin. The watersheds have extents in Arizona, Utah, New Mexico, US and Sonora, MX. Study focus: We calculated trends in total dissolved solids (TDS) concentrations and fluxes with the Weighted Regressions on Time, Discharge and Season model. The modeling framework leverages daily streamflow and discrete water quality observations at specific monitoring sites. We evaluated trends for a common period (1976–2008) and the whole period of record at each monitoring site in terms of climate and anthropogenic controls. New hydrologic insights for the region: Three rivers had persistent TDS concentrations exceeding the EPA secondary drinking water standard. All were associated with a geologic source of TDS. We observed increases and decreases in TDS concentrations at our monitoring sites, contrasting with global freshwater salinization and declining TDS concentrations in the Upper Colorado River Basin (UCRB). We attributed concentration variability to wintertime hydroclimatic forcing, with secondary influences of human water use. Reservoirs may decrease TDS concentrations by 50%. Efficiency improvements in irrigation and mining water uses may decrease TDS concentrations, while municipal growth increases TDS concentrations. We observed TDS flux declines at most monitoring sites. We attributed up to 85% of the TDS flux trend to changes in streamflow arising from drought and groundwater use. This study informs salinity dynamics in arid and aridifying locations, including the UCRB.

Lower Colorado River Basin↗

USGS2000

Water flow in the high plains aquifer in Northwestern Oklahoma

The High Plains is a major agricultural area, supported primarily by water from the High Plains aquifer, which is used to irrigate wheat and corn and to raise cattle and swine. The U.S. Geological Survey (USGS) and the Oklahoma Water Resources Board (OWRB) began a study of the High Plains aquifer in 1996. One purpose of the study was to develop a ground-water flow model that the OWRB could use to allocate the amount of water withdrawn from the a aquifer. The study area in Oklahoma covers all or parts of Beaver, Cimarron, Dewey, Ellis, Harper, Texas, and Woodward Counties. To provide appropriate hydrologic boundaries for the ground-water flow model, the study area was expanded to include parts of Colorado, Kansas, New Mexico, and Texas.

Oklahoma↗

USGS2026

Final project peport for “Mapping riparian vegetation response to climate change on the San Carlos Apache Reservation and Upper Gila River watershed to inform restoration priorities: 1935 to present – Phase 2: Focus on tamarisk vegetation”

Riparian ecosystems play a critical role in supporting wildlife habitats, maintaining water quality, and sustaining ecological resilience in arid landscapes. In the Upper Gila River level-4 Hydrologic Unit Code (HUC-4; Identification Number – 1504) watershed of Arizona and New Mexico, and across areas of the San Carlos Apache Tribe of the San Carlos Apache Reservation (hereafter, Tribe/Tribal – entity; or Reservation - place), riparian ecosystems have been substantially altered by the widespread expansion of tamarisk ( Tamarix spp.), an invasive and non-native riparian species. Tamarisk has high water use and increased flammability, making it a growing concern as droughts intensify across the southwestern United States (U.S.). Recent research indicates that tamarisk is increasingly stressed under prolonged drought conditions, which can elevate wildfire risk and further degrade riparian habitat. In response, the U.S. Geological Survey (USGS) Western Geographic Science Center, in collaboration with the Tribe, developed remote sensing–based tools to map riparian vegetation composition and monitor vegetation condition over time. These tools enable accurate identification of tamarisk extent, detection of vegetation stress, and comparison with native species such as cottonwood and willow. This information directly supports restoration and management actions, including targeted tamarisk removal, protection of endangered species habitat, and prioritization of areas for native vegetation recovery. The tools also provide insight into how riparian vegetation responds to changing climate and hydrologic conditions, strengthening long-term planning for riparian forest management. Findings from this work demonstrate that riparian vegetation responses vary across river systems, indicating differences in plant composition and hydro-climatic conditions. Tamarisk on both the Gila and San Carlos Rivers generally exhibit greater declines in greenness in response to higher temperature as well as lower precipitation and river flow, while cottonwood ( Populus fremontii ) and willow (Salix spp.) are particularly sensitive to changes in discharge along the San Carlos River and respond more directly to both high and low flows, with more moderate responses to precipitation and temperature. By providing actionable, science-based information, this research supports climate adaptation planning, wildfire risk reduction, and improved riparian ecosystem health, with benefits that extend beyond the Reservation to regional water and wildlife conservation efforts.

Arizona, New Mexico↗

USGS2006

Arizona black rattlesnake (Crotalus viridis cerberus)

The Arizona black rattlesnake makes its home at higher elevations in Arizona and far western New Mexico. The snake's use of high-altitude habitat and its black coloration as an adult distinguishes it from other subspecies of the western rattlesnake (Crotalus viridis), which prefer lower elevations and range from tan to reddish in color as adults. These physical and habitat differences are also reflected in genetic differences that suggest that the Arizona black rattlesnake may be a new species of rattlesnake. Despite the species's limited range, basic biological information needed to make management decisions is lacking for most Arizona black rattlesnake populations. To address this need, U.S. Geological Survey (USGS) scientists conducted research on the species in Arizona national park units from 2003 to 2005. The research examined relative population abundance, movement patterns, range requirements, dietary habits, and winter and summer habitat. Research in Arizona national parks was made possible through the support of the Western National Parks Association, Tonto National Monument, and the USGS Science Internships for Workforce Diversity Program. Importantly, the park-based research was used to augment a long-term mark-recapture study of the species that has been conducted by USGS biologists at sites near Flagstaff, Arizona, since 1999. USGS researchers were the first to conduct extensive studies of this species in the wild.

Fact Sheet↗

USGS2019

Anderson Ranch wetlands hydrologic characterization in Taos County, New Mexico

The Anderson Ranch property (study area), located in Taos County, north-central New Mexico, was transferred from Chevron Mining, Inc. (CMI) to the Bureau of Land Management (BLM) as part of a Natural Resource Damage Assessment and Restoration (NRDAR) court-ordered settlement. The study area supports freshwater emergent wetlands and freshwater ponds. The settlement states that CMI will provide the land and a monetary settlement to support the restoration of the wetlands on the property. To best manage the study area, the BLM requires an understanding of potential effects of climate variability and groundwater withdrawals on the wetland function. This study, completed by the U.S. Geological Survey in cooperation with the BLM, provides an initial hydrologic characterization of the study area, which included literature review, collection of groundwater-level and aqueous-chemistry data, completion of a vegetation survey, and preliminary data analysis. The data compiled, collected, and analyzed as part of this study indicate that the wetlands within the study area are groundwater fed and that the water maintaining the wetlands is modern. Surface-water levels in the pond and groundwater levels in the surrounding wetland fluctuate seasonally. The hydraulic gradient in the study area is from northeast to southwest. Evapotranspiration is a main driver of water demand within the study area.

New Mexico↗

USGS2006

Effects of roads and well pads on erosion in the Largo Canyon watershed, New Mexico, 2001-02

Largo Canyon, located in the San Juan Basin of northwestern New Mexico, is one of the longest dry washes in the world. Oil and gas production in the San Juan Basin, which began in the 1940's, required the development of an extensive network of dirt roads to service the oil and gas wells in the Navajo Reservoir area. Presently, there are about eight wells per square mile, and the density of oil and gas wells is expected to increase. Potential environmental effects on landscape stability that may result from the additional roads and well pads have not been documented. In 2001, the U.S. Geological Survey began a study in cooperation with the Bureau of Land Management to evaluate the effects of roads and well pads associated with oil and gas operations on the erosion potential of Bureau of Land Management lands in the Largo Canyon watershed. The effects of roads and well pads on erosion were quantified by installing sediment dams (dams) and by surveying transects across roads and well pads. Data from 26 dams were used in the analysis. Dams were installed at 43 sites: 21 on hillsides upslope from roads or pads to measure erosion from hillslopes, 11 at the downslope edges of roads to measure erosion from roads, and 11 at the downslope edges of well pads to measure erosion from well pads. Pairs of survey transects were established at nine well pads and two road locations. Sediment-accumulation data for 26 dams, recorded at 17 measurement intervals, indicate that average erosion rates at the dams significantly correlate to size of the contributing area. The average erosion rate normalized by drainage area was 0.001 foot per year below roads, 0.003 foot per year on hillslopes, and 0.011 foot per year below well pads. Results of a two-sample t-test indicate that there was no significant difference in average erosion rates for dams located on hillslopes and below roads, whereas average erosion rates were significantly greater for dams below well pads than for dams on hillslopes and dams below roads. The average erosion rates estimated from the data collected during this study most likely represent minimum erosion rates. Sediment-accumulation data for measurement intervals and for dams that were breached during 2002, resulting from the large volume of runoff generated by high-intensity storms, were not used to compute erosion rates. For this reason, the higher range of erosion rates is underrepresented and the results of this study are biased toward the lower end of the range of erosion rates. Measurements along road transects generally indicate that sediment is eroded from the top of road berms and redeposited at the base of the berms and may be transported downslope along the road. Measurements along well-pad transects generally indicate that sediment eroded from hillslopes is transported over the surface of the well pad and down the well-pad edges. Based on field observations, roads aligned parallel to topographic contours facilitate erosional processes in two ways: (1) roads cut across and collect runoff from previously established drainages and (2) roads, where they are cut into hillsides or into the land surface, provide focal points for the initiation of erosion. Roads aligned across topographic contours can serve as conduits to channel runoff but do not constitute a large percentage of the road network.

Scientific Investigations Report↗

USGS2008

Introduction to Field Water-Quality Methods for the Collection of Metals - 2007 Project Summary

The U.S. Geological Survey (USGS), Region VI of the U.S. Environmental Protection Agency (USEPA), and the Osage Nation presented three 3-day workshops, in June-August 2007, entitled ?Introduction to Field Water-Quality Methods for the Collection of Metals.? The purpose of the workshops was to provide instruction to tribes within USEPA Region VI on various USGS surface-water measurement methods and water-quality sampling protocols for the collection of surface-water samples for metals analysis. Workshop attendees included members from over 22 tribes and pueblos. USGS instructors came from Oklahoma, New Mexico, and Georgia. Workshops were held in eastern and south-central Oklahoma and New Mexico and covered many topics including presampling preparation, water-quality monitors, and sampling for metals in surface water. Attendees spent one full classroom day learning the field methods used by the USGS Water Resources Discipline and learning about the complexity of obtaining valid water-quality and quality-assurance data. Lectures included (1) a description of metal contamination sources in surface water; (2) introduction on how to select field sites, equipment, and laboratories for sample analysis; (3) collection of sediment in surface water; and (4) utilization of proper protocol and methodology for sampling metals in surface water. Attendees also were provided USGS sampling equipment for use during the field portion of the class so they had actual ?hands-on? experience to take back to their own organizations. The final 2 days of the workshop consisted of field demonstrations of current USGS water-quality sample-collection methods. The hands-on training ensured that attendees were exposed to and experienced proper sampling procedures. Attendees learned integrated-flow techniques during sample collection, field-property documentation, and discharge measurements and calculations. They also used enclosed chambers for sample processing and collected quality-assurance samples to verify their techniques. Benefits of integrated water-quality sample-collection methods are varied. Tribal environmental programs now have the ability to collect data that are comparable across watersheds. The use of consistent sample collection, manipulation, and storage techniques will provide consistent quality data that will enhance the understanding of local water resources. The improved data quality also will help the USEPA better document the condition of the region?s water. Ultimately, these workshops equipped tribes to use uniform sampling methods and to provide consistent quality data that are comparable across the region.

Fact Sheet↗

USGS2022

Significance of U-Pb detrital zircon geochronology for mudstone provenance

Detrital zircon U-Pb studies of mudstone provenance are rare but may preferentially fingerprint distal zircon sources. To examine this issue, Pierre Shale and Trinidad Sandstone deposited in a Late Cretaceous deltaic environment in the Raton Basin, Colorado (USA), were measured for detrital zircon U-Pb age by laser ablation–inductively coupled plasma–mass spectrometry. Two major detrital zircon age peaks at ca. 70 and 1690 Ma are found in both Pierre Shale and Trinidad Sandstone but in inversely varying proportions: 68% and 16%, respectively, for the finest zircon fraction (~15–35 μm) in the shale, and 25% and 32%, respectively, for the coarsest zircon fraction (~60–80 μm) in the sandstone. Proximal sources in the Sangre de Cristo Mountains, directly west of the Raton Basin, contain coarse-grained, ca. 1690 Ma zircon, whereas distal sources in Laramide uplifts and basins in Colorado, New Mexico, and Arizona contain fine-grained, ca. 70 Ma zircon. The results indicate that U-Pb zircon provenance of mudstone reflects availability of volcanic and other fine-grained source rocks rather than simply distal sources. U-Pb zircon provenance studies should routinely include mudstone units because these units may identify fine-grained zircon sources more reliably than sandstones alone.

Arizona, Colorado, New Mexico, Utah↗

USGS1973

The Late Cretaceous ammonite Baculites undatus Stephenson in Colorado and New Mexico

Baculites undatus Stephenson, originally described from the Nacatoch Sand of northeastern Texas, has been found in the Pierre Shale at 25 localities in Colorado and two in New Mexico. An early form of the species occurs in the zone of Didymoceras cheyennense (Meek and Hayden), and the typical form occurs in the overlying zones of Baculites compressus Say, B. cuneatus Cobban, and B. reesidei Elias. The species is characterized by its stout cross section, broad venter, conspicuous lateral and ventral ribs, and suture of about average complexity for the genus.

Colorado, Wyoming, New Mexico↗

USGS2005

Mineralogical and geochemical consequences of the long-term presence of CO2 in natural reservoirs: An example from the Springerville-St. Johns Field, Arizona, and New Mexico, U.S.A

The Springerville-St. Johns CO2 field in eastern Arizona and western New Mexico is one of more than a dozen gas fields developed within the Colorado Plateau and Southern Rocky Mountain region. Extensive travertine (CaCO3) deposits record a long history of CO2 migration and leakage to the atmosphere. The oldest travertine deposits may have formed during the initial filling of the CO2 reservoir when groundwaters exsolved CO2 upon reaching the surface. The youngest travertine deposits are associated with springs on the floor of the Little Colorado River valley, but travertine deposition appears to be insignificant today. Older deposits occur up to 325 m above the valley floor. Geologic relationships suggest travertine deposition began in the late Pleistocene after volcanic activity ended at ???0.3 Ma. Most of the CaCO3 could have been derived from dissolution of the underlying limestones and dolomites. Interactions between the reservoir fluids and rocks were observed in core samples from one of the intervals that produced dry gas. These reactions resulted in the dissolution of carbonate cements and detrital feldspars and the formation of dawsonite and kaolinite. Geochemical simulations suggest that the dawsonite could have been deposited when the CO2 fugacity reached 20 bars and that the kaolinite formed as the CO2 fugacity decreased. Corrosion of drill pipe by acidic waters and a pronounced HCO3 anomaly above the CO2 reservoir provide evidence of a continuing flux of CO2 from depth. CO2 storage occurs primarily as dissolved carbonate species and as gas accumulations. Only a small percentage of the CO2 was sequestered in secondary minerals. ?? 2005 Elsevier B.V. All rights reserved.

Chemical Geology↗

USGS2002

Measuring streamflow in Virginia (2002 revision)

The U.S. Geological Survey (USGS), U.S. Department of the Interior, is the Nation's largest Earth-science information agency. Among its many responsibilities, such as map making and providing information on earthquakes and other natural hazards, the USGS provides information on the Nation's water resources. The USGS has collected and analyzed hydrologic (water-related) information for more than 100 years. In 1889, the first streamflow-gaging station (a site where regular observations of streamflow data are collected) operated in the United States by the USGS was established on the Rio Grande near Embudo, New Mexico. As the need for streamflow data increased, the USGS's streamflow-gaging program has grown to include more than 7,000 continuous-record streamflow-gaging stations. More than 90 percent of these stations are operated with at least partial support from State, local, or other Federal agencies In Virginia, the Department of Environmental Quality (DEQ) is a major cooperator in the streamflow-gaging program, which consists of 161 continuous-record streamflow-gaging stations located throughout the State (fig. 1). The USGS and DEQ cooperate to publish the annual USGS State data report, 'Water Resources Data-Virginia'; this two-volume publication includes streamflow data collected at the 161 streamflow-gaging stations, chemical data collected at 19 streamflow-gaging stations, and ground-water data collected from more than 250 wells located in Virginia.

Virginia↗

USGS1999

Measuring streamflow in Virginia (1999 revision)

The U.S. Geological Survey (USGS), U.S. Department of the Interior, is the Nation's largest Earth-science information agency. Among its many responsibilities, such as map making and providing information on earthquakes and other natural hazards, the USGS provides information on the Nation's water resources. The USGS has collected and analyzed hydrologic (water-related) information for more than 100 years. In 1889, the first streamflow-gaging station (a site where regular observations of streamflow data are collected) operated in the United States by the USGS was established on the Rio Grande near Embudo, New Mexico. As the need for streamflow data increased, the USGS's streamflow-gaging program has grown to include more than 7,000 continuous-record streamflow-gaging stations. More than 90 percent of these stations are operated with at least partial support from State, local, and other Federal agencies. In Virginia, the Department of Environmental Quality (DEQ) is a major cooperator in the streamflow-gaging program, which consists of 152 continuous-record streamflow-gaging stations located throughout the State (fig. 1). The USGS and DEQ cooperate to publish the annual USGS State data report, "Water Resources Data-Virginia;" this two-volume publication includes streamflow data collected at the 152 streamflow-gaging stations, chemical data collected at more than 24 streamflow-gaging stations, and ground-water data collected from more than 338 wells.

Virginia↗

USGS2002

Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado

New 1:24,000-scale geologic mapping along the Interstate-70 urban corridor in western Colorado, in support of the USGS Central Region State/USGS Cooperative Geologic Mapping Project, is contributing to a more complete understanding of the stratigraphy, structure, tectonic evolution, and hazard potential of this rapidly developing region. The 1:24,000-scale Dillon quadrangle is near the headwaters of the Blue River and straddles features of the Blue River graben (Kellogg, 1999), part of the northernmost reaches of the Rio Grande rift, a major late Oligocene to recent zone of extension that extends from Colorado to Mexico. The Williams Range thrust fault, the western structural margin of the Colorado Front Range, cuts through the center of the quadrangle, although is mostly covered by surficial deposits. The oldest rocks in the quadrangle underlie the Williams Fork Mountains and the ridge immediately east of South Fork Middle Fork River, and include biotite-sillimanite schist and gneiss, amphibolite, and migmatite that are intruded by granite inferred to be part of the 1,667-1,750 Ma Routt Plutonic Suite (Tweto, 1987). The oldest exposed sedimentary unit is the Upper Jurassic Morrison Formation, but Pennsylvanian Maroon Formation, a sequence of red sandstone, conglomerate, and interbedded shale, underlies the southern part of the quadrangle. The thickest sequence of sedimentary rocks is Cretaceous in age and includes at least 500 m of the Upper Cretaceous Pierre Shale. Surficial deposits include (1) an old, deeply dissected landslide deposit, possibly as old as Pliocene, on the west flank of the Williams Fork Mountains, (2) deeply weathered, very coarse gravel deposits underlying a mesa in the southwest part of the quadrangle (the Mesa Cortina subdivision. The gravels are gold bearing and were mined by hydraulic methods in the 1800s), (3) moderately to deeply weathered, widespread, bouldery material that is a combination of till of the Bull Lake glaciation, debris-flow deposits, landslide deposits, and possibly pre-Bull Lake till, (4) glacial deposits of both Bull Lake (middle Pleistocene) and Pinedale (late Pleistocene)glaciations, (5) recent landslide deposits, and (6)extensive colluvial and alluvial deposits.

Miscellaneous Field Studies Map↗

USGS1997

Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado

Colorado↗

USGS2016

Geologic map of the Rio Rico and Nogales 7.5’ quadrangles, Santa Cruz County, Arizona

The Rio Rico and Nogales (Arizona) 1:24,000-scale quadrangles are located in the Basin and Range Province of southern Arizona, and the southern edge of the map is the international border with Sonora, Mexico. The major urban area is Nogales, a bi-national city known as “the gateway to Mexico.” Rocks exposed in the map area range in age from Jurassic through Quaternary. Major physiographic, geologic, and hydrologic features in the map area include the southern San Cayetano Mountains, Grosvenor Hills, and Sonoita Creek in the northern part, and Mount Benedict and the Mount Benedict horst block in the southcentral part. The horst block is bounded by the Santa Cruz River on the east and Nogales Wash on the west. The objectives of our mapping were to define the geologic framework for the Nogales area and the upper Santa Cruz basin to support ongoing multidisciplinary projects. This new work will improve understanding of the Nogales Formation to more fully assess its groundwater resource potential. We significantly revised the Miocene Nogales Formation based on geologic mapping combined with new geochronologic, geophysical, and petrographic studies.

Arizona↗

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,↗

USGS2011

Changes in water levels and storage in the High Plains Aquifer, predevelopment to 2009

The High Plains aquifer underlies 111.8 million acres (175,000 square miles) in parts of eight States - Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The area overlying the High Plains aquifer is one of the primary agricultural regions in the Nation. Water-level declines began in parts of the High Plains aquifer soon after the onset of substantial irrigation with groundwater from the aquifer (about 1950 and termed "predevelopment" in this fact sheet). By 1980, water levels in the High Plains aquifer in parts of Texas, Oklahoma, and southwestern Kansas had declined more than 100 feet (ft) (Luckey and others, 1981). In 1987, in response to declining water levels, Congress directed the U.S. Geological Survey (USGS), in collaboration with numerous Federal, State, and local water-resources entities, to assess and track water-level changes in the aquifer. This fact sheet summarizes changes in water levels and drainable water in storage in the High Plains aquifer from predevelopment to 2009. Drainable water in storage is the fraction of water in the aquifer that will drain by gravity and can be withdrawn by wells. The remaining water in the aquifer is held to the aquifer material by capillary forces and generally cannot be withdrawn by wells. Drainable water in storage is termed "water in storage" in this report. A companion USGS report presents more detailed and technical information about water-level and storage changes in the High Plains aquifer during this period (McGuire, 2011).

Colorado;Kansas;Nebraska;New Mexico;Oklahoma;South↗