Unified Interior Regions
Region 7: Upper Colorado Basin
Map of Region 7 Upper Colorado River Basin

Map Showing USGS/DOI Unified Region 7 and parts of adjoining Regions
Key USGS Region 7 Upper Colorado Basin Contacts
Regional Director (Acting)-Peter Griffiths
Associate Regional Director, Operations-Peter Griffiths
USGS Region 7 Upper Colorado Basin Offices and Science Centers
Regions L2 Landing Page Tabs
USGS Science Centers in Region 7-Upper Colorado Basin conduct a large number of cooperative and collaborative projects with other agencies and partners. A sampling of those projects are shown below on this web page.
Water-Budget Analysis of the Upper Big Sandy Alluvial Aquifer
The Upper Big Sandy Groundwater Management District is concerned with potentially declining groundwater levels and thus available groundwater in storage for the Upper Big Sandy alluvial aquifer in eastern Colorado
This project evaluated changes in groundwater storage within the Upper Big Sandy Designated Groundwater Basin by updating water-budget results for the alluvial aquifer from...
Paradox Valley Total Dissolved Solids (TDS) Regression Equations
The primary objective of the project is to evaluate and update previous regression equations, developed for the USGS streamgages and continuous water-quality records,that describe the relation between specific conductance measured in the Dolores River and calculated total dissolved solids TDS. A secondary objective is to evaluate brine discharge to the river using a previously developed...
Land Treatment Digital Library
The LTDL was created by the U.S. Geological Survey (USGS) to catalog information about land treatments on Federal lands in the western United States for all interested parties. The flexible framework of the library allows for the storage of a wide variety of data in different formats. The LTDL currently stores previously established land treatments or what often are called legacy data. The...
Reconstructing Flow History From Riparian Tree Rings
Aquatic Systems Branch scientists analyze rings of riparian trees relating tree growth and establishment to historical flow. We then use the tree rings to reconstruct the flow in past centuries. Flow reconstructions discover the frequency and magnitude of past droughts and floods—information that is essential for management of rivers and water supplies. We also use downscaled climate...
RestoreNet: Distributed Field Trial Network for Dryland Restoration
U.S. Geological Survey (USGS) researchers and land managers are co-producing a network of restoration field trial sites on DOI and surrounding lands in the southwestern U.S. The network systematically tests restoration treatments across a broad range of landscape, soil, and climate conditions. Each site in the network is used to test suitable seed mixes and treatments that promote plant...
Burned Area Essential Climate Variable
Essential Climate Variables (ECVs) track critical attributes of the atmosphere, oceanic, and terrestrial systems over time-scales appropriate for analyzing their relationships with climate change. As part of a larger Climate Data Record (CDR) and ECV project, scientists at GECSC are leading the development and validation of the Burned Area ECV algorithm. This algorithm automatically extracts...
Cenozoic Landscape Evolution of the Southern Rocky Mountains
The Cenozoic Landscape Evolution of the Southern Rocky Mountains Project is a multi-year investigation funded by the National Cooperative Geologic Mapping Program. This project utilizes a combination of geologic mapping, geophysical surveys, basin modeling, and structural, neotectonic, geomorphic, volcanic, stratigraphic, and geochronologic studies to better understand the geologic landscape...
Ecosystem Services Assessment and Valuation
Ecosystem services are the benefits that nature provides to human well-being: clean air and water, protection from natural disasters, fisheries, crop pollination and control of pests and disease, and outdoor places for recreation, solitude, and renewal. Ecosystem services underlie the functioning of our entire economy. They are neither worthless nor priceless, and by integrating the physical...
Effects of Energy Development Strategies
Energy is a cornerstone issue for humanity, nations, and individuals. How we create and use energy impacts the consequences it embodies. The critical issue facing humanity involves meeting our massive and growing energy needs, without undermining human and natural capital. Facing the challenge of long-term, sustainable energy for the nation and world requires understanding the consequences of...
Exploring Future Flora, Environments, and Climates Through Simulations (EFFECTS)
Climate changes can significantly affect species and ecosystems. Historical and paleoenvironmental data record species and ecosystem responses to past climate changes, but these records become sparse as one goes further back in time. Model simulations can be used fill the spatial and temporal gaps in observed records to improve our understanding of the potential magnitude, rate, and spatial...
Geologic Mapping Studies at Buffalo National River, Northern Arkansas
Detailed geologic mapping is being conducted by the USGS in and adjacent to the Buffalo National River, a park administered by the National Park Service, to better understand and characterize the natural resources and associated ecosystems of this area within the Ozark Plateau region. General-purpose geologic maps are created to provide a framework for a host of natural resource, natural...
Geologic Records of High Sea Levels
This project studies past high sea levels on coastlines that preserve fossil coral reefs or marine terraces. We ascertain the magnitudes of sea-level high stands by field mapping, stratigraphic measurements, and precise elevation measurements. Geochronology is accomplished by radiocarbon dating of mollusks (for Holocene-to-last-glacial deposits), uranium-series dating of corals (for high-sea...
USGS Science Centers in Region 7-Upper Colorado Basin collect a wide variety of natural resource data types including spatial, geologic, hydrologic, and biologic data. Data included in USGS-series publications that are not publically available in USGS databases are published in Data Releases. Tools are USGS products that can be used to analyze those types of data.
Datasets of ecological communities (invertebrates and fish), streamflow, habitat, and water quality to examine the presence of trends in ecological communities from the Fountain Creek Basin, Colorado, USA, 2003-2016
These data were used for an analysis as part of a long-term project monitoring the biological communities, habitat, and water quality of the Fountain Creek Basin. Biology, habitat, and water quality data have been collected at 10 sites starting in 2003. These data include annual samples of aquatic invertebrate communities, fish communities, water quality, and quantitative riverine habitat...
SFR Inflow Table for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This tabular dataset represents monthly flow at 18 surface-water inflow points used as input into the Streamflow-Routing (SFR) Package for MODFLOW-One-Water Hydrologic Flow Model in the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM). Fourteen of the inflow points represent wastewater treatment plant (WWTP)/water reclamation plant outfalls, two of the inflow points r
Texas Water Development Board Wells: Municipal and Industrial Monthly Pumping Rates for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This dataset contains monthly pumping rates for municipal and industrial (MnI) wells in Texas within the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM) that were not included in other pumping rate datasets. In RGTIHM, these wells are considered the Texas Water Development Board (TXWDB) group. Monthly pumping rates are presented in units of cubic feet per day for the p
Output Data Metadata, 2012 Little Bear Fire PRMS prefire-postfire models
This dataset contains output files from hydrologic simulations of the Upper Rio Hondo Subbasin, New Mexico using the Precipitation-Runoff Modeling System (PRMS). Input data for the entire Upper Rio Hondo Subbasin were developed, but output data only from the North Fork Eagle Creek subwatershed were used. Output datasets for four model simulations are included: two calibrated model simul
Allocation by Service Units
This dataset contains annual surface-water diversion allocations from 1940 through 2014 for the six canal service units used in the Lower Rio Grande Basin groundwater flow model (SSPA, 2007). Allocation values were derived from annual Rio Grande Project surface-water diversion allocations to lands within New Mexico and Texas extracted from the Allocation spreadsheet (Ferguson, I., Bur
NMOSE Agricultural GW Pumping
This dataset contains annual agricultural groundwater pumping values in 1975 for Doña Ana County; in 1980, 1985, 1990, 1994, 1995, 2000, 2005, and 2010 for Doña Ana and Sierra Counties; and in 2009, 2011, 2012, 2013, and 2014 for the Lower Rio Grande Water Master District in New Mexico. Groundwater pumping values were extracted from Sorensen (1977), Soren
Cross-Section Geometry at Two Bridges over the Gunnison River in Western Colorado, 2016–17
This dataset contains cross-section surveys of the Gunnison River at Colorado Department of Transportation bridges I-04-K and I-03-A, western Colorado, 2016–17. The surveys were performed using a combination of: Trimble R8 Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) receiver, a USGS bridge crane with sounding weights, and optical levels. During surveys performed...
Stream Segments for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This line vector dataset represents the Rio Grande, engineered surface-water conveyance structures (canals, laterals, drains, and wasteways), diversions to water-balance subregions (WBS), and the Las Cruces Arroyo segments simulated with the Streamflow-Routing (SFR) Package for MODFLOW-One-Water Hydrologic Flow Model in the Rio Grande Transboundary Integrated Hydrologic Mo
SFR Tributary Inflow Table for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This tabular dataset represents monthly flow at 80 tributary pour points (see the RGTIHM_Tributary_Pour_Pts feature class) used as model boundary inflow locations to tributaries (see the RGTIHM_Tributaries feature class) simulated with the Streamflow-Routing (SFR) Package for MODFLOW-One-Water Hydrologic Flow Model in the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM%
Las Cruces, New Mexico Wells: Municipal and Industrial Monthly Pumping Rates for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This dataset contains monthly pumping rates for municipal and industrial (MnI) wells in the City of Las Cruces, New Mexico network within the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM). In RGTIHM, these wells are considered the Las Cruces, New Mexico (LCNM) group. Monthly pumping rates are presented in units of cubic feet per day for the period from March 1940
Canutillo, Texas Wells: Municipal and Industrial Monthly Pumping Rates for the Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and Northern Chihuahua, Mexico
This dataset contains monthly pumping rates for municipal and industrial (MnI) wells in the Canutillo, Texas network within the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM). In RGTIHM, these wells are considered the Canutillo, Texas (TXCN) group. Monthly pumping rates are presented in units of cubic feet per day for the period from March 1940 through December 20
Data release for Time series of high-resolution images enhances efforts to monitor post-fire condition and recovery, Waldo Canyon fire, Colorado, USA
Interpretations of post-fire condition and rates of vegetation recovery can influence management priorities, actions, and perception of latent risks from landslides and floods. In this study, we used the Waldo Canyon fire (2012, Colorado Springs, Colorado, USA) as a case study to explore how a time series (2011-2016) of high-resolution images can be used to delineate burn exte
USGS Science Centers in Region 7-Upper Colorado Basin produce hundreds of USGS-series publications, journal papers, and books each year that are subject to rigorous review by USGS specialists. The publications shown below on this page are related to study areas and staff members of USGS Science Centers in Region 7 compiled from the USGS Publications Warehouse.
Magnetic field variations in Alaska: Recording space weather events on seismic stations in Alaska
Seismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors...
Ringler, Adam T.; Anthony, Robert E.; Wilson, David C.; Claycomb, Abram E.; Spritzer, JohnEvidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex
Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8–1.7 Ga). Hundreds of meters of Paleozoic...
Drenth, Benjamin J.; Souders, A. Kate; Schulz, Klaus J.; Feinberg, Joshua M.; Anderson, Raymond R.; Chandler, Val W.; Cannon, William F.; Clark, RyanA rasterized building footprint dataset for the United States
Microsoft released a U.S.-wide vector building dataset in 2018. Although the vector building layers provide relatively accurate geometries, their use in large-extent geospatial analysis comes at a high computational cost. We used High-Performance Computing (HPC) to develop an algorithm that calculates six summary values for each cell in a raster...
Pourpeikari Heris, Mehdi; Foks, Nathan Leon; Bagstad, Kenneth J.; Troy, Austin; Ancona, Zachary H.Design and operations of the Hydrate 01 Stratigraphic test well, Alaska North Slope
The National Energy Technology Laboratory, the Japan Oil, Gas and Metals National Corporation, and the U.S. Geological Survey are leading an effort to conduct an extended gas hydrate production test in northern Alaska. The proposed production test required the drilling of an initial stratigraphic test well (STW) to confirm the geologic conditions...
Collett, Timothy S.; Zyrianova, Margarita V.; Okinaka, Norihiro; Wakatsuki, Motoi; Boswell, Ray; Marsteller, Scott; Minge, David; Crumley, Stephen; Itter, David; Hunter, Robert D.Procedure for calculating estimated ultimate recoveries of wells in the Wolfcamp shale of the Midland Basin, Permian Basin Province, Texas
In 2016, the U.S. Geological Survey published an assessment of technically recoverable continuous oil and gas resources of the Wolfcamp shale in the Midland Basin, Permian Basin Province, Texas. Estimated ultimate recoveries (EURs) were calculated with production data from IHS MarkitTM using DeclinePlus software in the Harmony interface. These...
Leathers-Miller, Heidi M.Alaska North Slope 2018 Hydrate-01 Stratigraphic Test Well: Technical results
The Hydrate-01 Stratigraphic Test Well was drilled in December 2018 to confirm that a seismically-identified location within the western Prudhoe Bay Unit might be suitable for extended-duration scientific production testing. The well tested two primary targets: the deeper Unit B is highly favorable due to optimal reservoir temperature and minimal...
Boswell, Ray; Collett, Timothy; Suzuki, Kiyofumi; Yoneda, Jun; Haines, Seth S.; Okinaka, Nori; Tamaki, Machiko; Crumley, Stephen; Itter, David; Hunter, RobertGas hydrate saturation estimation from acoustic log data in the 2018 Alaska North Slope Hydrate-01 stratigraphic test well
Completed in December 2018, the Alaska North Slope Hydrate 01 stratigraphic test well provides a wealth of logging-while-drilling (LWD) data for strata to below the base of gas hydrate stability (BGHS). This well is intended to be the first of three wells drilled for a long-term gas hydrate production test to be conducted by the U.S. Department...
Haines, Seth S.; Collett, Timothy; Boswell, Ray; Lim, Teck; Okinaka, Nori; Suzuki, Kiyofumi; Fujimoto, AkiraCritical evaluation of stable isotope mixing end-members for estimating groundwater recharge sources: Case study from the South Rim of the Grand Canyon, Arizona, USA
Springs and groundwater seeps along the South Rim of the Grand Canyon serve an important function for the region’s ecosystems, residents (both human and wild animal), and economy. However, these springs and seeps are potentially vulnerable to contamination, increased groundwater extraction, or reduced recharge due to climate change. Protection of...
Solder, John E.; Beisner, Kimberly R.'Dust in the wind’ from source-to-sink: Analysis of the 14-15 April 2015 storm in Utah
On 14–15 April 2015, an intense intermountain cyclone in the western USA caused high winds and a dust storm that degraded air quality in the eastern Great Basin, and deposited dust-on-snow (DOS) in the Wasatch Range near Salt Lake City, Utah. We analyzed the storm and documented its “source-to-sink” development to relate the frontal passage with...
Nicoll, Kathleen; Hahnenberger, Maura; Goldstein, Harland L.Surface displacement distributions for the July 2019 Ridgecrest, California earthquake ruptures
Surface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left‐lateral and northeast‐striking rupture in the Mw">Mw 6.4 foreshock and dominantly right‐lateral and northwest‐striking rupture in the Mw">Mw 7.1 mainshock. We present >...
Duross, Christopher; Gold, Ryan D.; Dawson, Timothy E.; Scharer, Katherine; Kendrick, Katherine; Akciz, Sinan; Angster, Stephen J.; Bachhuber, Jeffery; Bacon, Steven; Bennett, Scott E. K.; Blair, Luke; Brooks, Benjamin A.; Bullard, Thomas; Burgess, W. Paul; Chupik, Colin; DeFrisco, Michael; Delano, Jaime; Dolan, James D.; Frost, Erik; Graehl, Nick; Haddon, Elizabeth; Hatem, Alexandra Elise; Hernandez, Janis; Hitchcock, Christopher S.; Hudnut, Kennth; Thompson Jobe, Jessica; Koehler, Richard D; Kozaci, Ozgur; Ladinsky, Tyler C.; Madugo, Christopher; McPhillips, Devin; Milliner, Christopher; Morelan, Alexander; Olson, Brian; Patton, Jason; Philibosian, Belle; Pickering, Alexandra J.; Pierce, Ian; Ponti, Daniel J.; Seitz, Gordon G.; Spangler, Eleanor; Swanson, Brian J.; Thomas, Kate; Treiman, Jerome; Valencia, Francesca; Williams, Alana; Zinke, RobertAssessment of continuous oil and gas resources in the Ordovician Collingwood Formation and Utica Shale of the Michigan Basin Province, 2019
Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 290 milllion barrels of shale oil and 7.9 trillion cubic feet of shale gas in the Ordovician Collingwood-Utica Shale Total Petroleum System of the Michigan Basin Province.
Schenk, Christopher J.; Mercier, Tracey J.; Woodall, Cheryl A.; Leathers-Miller, Heidi M.; Finn, Thomas M.; Le, Phuong A.; Brownfield, Michael E.; Marra, Kristen R.; Ellis, Geoffrey S.Geochemical characterization of groundwater evolution south of Grand Canyon, Arizona (USA)
Better characterization of the geochemical evolution of groundwater south of Grand Canyon, Arizona (USA), is needed to understand natural conditions and assess potential effects from breccia-pipe uranium mining in the region. Geochemical signatures of groundwater at 28 sampling locations were evaluated; baseline concentrations for select trace...
Beisner, Kimberly R.; Solder, John E.; Tillman, Fred; Anderson, Jessica; Antweiler, Ronald C.Photos and videos described and linked on this webpage come from a wide variety of USGS science activities and presentations performed by USGS Science Center staff members in the Region 7-Upper Colorado Basin.
Precipitation Runoff Modeling System (PRMS) Surface-Runoff Modules
Presents descriptions of the USGS Precipitation Runoff Modeling System (PRMS) Surface-Runoff modules, which compute Hortonian surface runoff, soil infiltration, and impervious surface and surface depression storage and flows.
New Breach Allows Flow on the Great Salt Lake
The new Great Salt Lake breach was opened on Dec. 1 by the Union Pacific Railroad Company. This created a new opening between the north and the south arm of the lake, allowing water to flow between the two sides. This time-lapse video shows the breach opening, which took about two hours. Before the new breach was opened, the north arm of the Great Salt Lake was at an
Rio Chama above Abiquiu Dam
Snowy road on the way to Rio Chama above Abiquiu Dam (08286500)
Lake Powell
Lake Powell
Devils Tower - Unmanned Aircraft System
This image of Devils Tower National Monument was created by combining elevation data and a digital photograph, captured over the landmark the same time by an unmanned aircraft system (UAS) in 2016.
Rio Brazos near Tierra Amarilla, NM
Hydrologic technician Lindsay Hastings took this photo of the Rio Brazos near Tierra Amarilla, New Mexico during her first field trip as a streamgager with the New Mexico Water Science Center. Did you know that New Mexico was the birth place of streamgaging? The USGS began collecting streamflow information in 1889 when the first streamgage was established on the Rio Grande
...Nature's Balance — Schwabacher's Landing
This was an early morning capture as the sun was rising at Schwabacher's Landing, Wyoming. The heavy cloud cover shielded the Grand Tetons from full view, but as we sat there, a small sliver of the mountains peeked through the clouds just long enough to take a few shots. In this shot, you can see two banks of the Snake River converging in the center and pointing toward the
...Grand Tetons
A shot taken from the walkway behind the Jackson Lake Lodge in Grand Teton National Park, Wyoming.
(From NPS site) Grand Teton National Park was established in 1929; Jackson Hole National Monument was created in 1943. The two units were combined to become the present Grand Teton National Park in 1950. The park is 45 miles in length from north to south, 26 miles
...Eureka Graben, Silverton caldera complex, CO
USGS scientist David Fey walking through the Eureka Graben in the Silverton caldera complex.
USGS scientist Jayne Belnap examines instruments to measure biocrust
USGS scientist Jayne Belnap examines instrumentation to measure photosynthetic rates of biocrusts.
Arid and semiarid ecosystems are expected to experience significant changes in temperature and precipitation patterns, which may affect soil organisms in ways that cause surfaces to become lighter in color and thus reflect more sunlight, according to a new USGS study
...Footprint damage to biocrusts
Many human activities can be unintentionally harmful to biological crusts. The biocrusts are no match for the compressional stress caused by footprints of livestock or people or tracks from vehicles.
Arid and semiarid ecosystems are expected to experience significant changes in temperature and precipitation patterns, which may affect soil organisms in ways that
...News items shown on this page are highlights of selected studies conducted and publications produced by USGS Science Center staff members in Region 7-Upper Colorado Basin.
Three sites on the Powder River show a difference in water quality between the time prior to coalbed methane development and during the production period, according to a new U.S. Geological Survey report.
The USGS, in cooperation with other Federal agencies, has posted new Idaho US Topo quadrangles (1,193) and New Mexico quads (1,980 maps) which include Public Land Survey System (PLSS). These are added to the growing list of states west of the Mississippi River to have PLSS data added to US Topo maps.
What is all the buzz about in the Yellowstone area? Is it really dangerous? On January 23rd Jake Lowenstern, Scientist-in-Charge of Yellowstone Volcano Observatory will explain what is happening now with earthquakes, ground uplift, and steam explosions.
Low concentrations of chemicals commonly used at airports for de-icing planes were detected in samples of groundwater collected from the Snake River alluvial aquifer beneath the Jackson Hole Airport.
Secretary of the Interior Sally Jewell announced today that Interior’s Southwest Climate Science Center is awarding nearly $1.2 million to universities and other partners for research to guide managers of parks, refuges and other cultural and natural resources in planning how to help species and ecosystems adapt to climate change.
Secretary of the Interior Sally Jewell announced today that Interior's North Central Climate Science Center is awarding slightly more than one million dollars to universities and other partners for research to guide managers of parks, refuges and other cultural and natural resources in planning how to help species and ecosystems adapt to climate change.
Secretary of the Interior Sally Jewell announced today that Interior’s South Central Climate Science Center is awarding about $1.2 million to universities and other partners for research to guide managers of parks, refuges and other cultural and natural resources in planning how to help species and ecosystems adapt to climate change.
Drought conditions are linked to declines in a protected desert tortoise population in part of the Sonoran Desert, according to a U.S. Geological Survey study.
Growth of algae and other aquatic plants is greater in Fish Creek than in nearby rivers and streams, according to a new U.S. Geological Survey report. This excess algae is related to the influx of nutrients, orthophosphate and nitrate, to the stream from groundwater and can lead to various environmental issues.
The U.S. Geological Survey's Wyoming and Montana water science centers will merge in October, improving science capacity and capabilities by integrating scientists in the two centers and allowing them to share equipment and expertise.
The mere presence of wolves, previously shown to affect the behavior of elk in the greater Yellowstone ecosystem, is not potent enough to reduce the body condition and reproductive rates of female elk, according to new research published today.
Diving deep into the mechanics of bedrock incision caused by debris flows, scientists now have a better understanding of the erosive forces responsible for cutting valleys into mountainous terrain, according to recently published research in the Journal of Geophysical Research-Earth Surface.
This page includes links to Social Media accounts (top of page), Science Centers (middle of page), and Regional Office staff members (bottom of page) of the USGS Region 7--Upper Colorado Basin.
USGS Science Centers in Region 7-Upper Colorado Basin conduct a large number of cooperative, co-funded science and monitoring projects with many other Federal, Tribal, State, and local agencies. Please scroll below to see the agencies with which those Science Centers currently have cooperative agreements.