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At least 667 records · Page 37Linked to original sources
USGS1977

Preliminary study of subsurface wastewater movement in and near Grand Teton National Park, Wyoming, through October 1976

Investigations were made by the U.S. Geological Survey in cooperation with Teton County, Wyoming and the National Park Service to determine the effects on nearby lakes and streams of percolating wastewater effluent at three sites in and near Grand Teton National Park. Observation wells were drilled at two of the sites, and water samples were collected from the wells. Sites were established on selected streams to collect water samples and to measure streamflow. Sufficient data have not been collected at this time to determine in detail the baseline quality of water in the selected streams or the rate, direction, and velocity of movement of percolating effluents. However, theoretical concepts and data collected to date suggest that effluent percolating near Colter Bay Village is most likely moving westward and southwestward toward Swan Lake and Colter Bay. Effluent percolating near Moose is most likely moving southeastward and southward toward the Snake River. Effluents near Flagg Ranch and Huckleberry Hot Springs probably discharge into the Snake River and Polecat Creek, but the amounts are small. (Woodard-USGS)

Open-File Report↗
USGS1976

Preliminary study of wastewater movement in Yellowstone National Park, Wyoming, July 1975 through September 1976

This report describes a study by the U.S. Geological Survey in cooperation with the National Park Service to determine the effects on nearby lakes and streams of wastewater effluents that percolate from sewage lagoons at four sites in Yellowstone National Park. A network of observation wells has been established near the sites, and data have been collected from the wells and from nearby streams. Ground-water mounds have built up under the lagoons as percolation of effluents occurred. Percolating effluents mix with ground water and form plumes of ground water that contain chemical constituents for the effluents. Each plume tends to move down the hydraulic gradient in a direction generally perpendicular to the water-level contours. Water-level contours and most likely areas of movement of the plumes are shown on maps. Tests using rhodamine WT dye and dissolved solids as tracers suggested that chemical constituents in the plumes travel at different velocities as a result of dispersion and adsorlption. Chemical constituents from effluent percolating from the Old Faithful lagoons probably discharge into nearby Iron Spring Creek. Constituents from lagoons at the other three sites studied probably have not reached nearby streams or lakes. (Woodard-USGS)

Open-File Report↗
USGS1978

Potential potable-water supplies in Redwood National Park, California

An evaluation was made of the potential for potable-water supplies at 13 sites in or near Redwood National Park, Calif. The National Park Service is planning for the development of visitor facilities at these sites. At some sites, the report recommends using surface-water diversions. At other sites, locations are given for test-well drilling or springs are recommended for development. Chemical analyses of water are given for selected surface-water supplies and for some existing wells and springs. The chemical quality of the water is suitable at most of the sites, although concentrations of iron and chloride are excessively high in some areas.

California↗
USGS1979

Chemical analyses of coal and coal-associated rock samples from the Coalmont Formation, McCallum and Coalmont areas, North Park, Jackson County, Colorado

As part of a continuing program by the U.S. Geological Survey to collect and chemically analyze representative samples of U.S. coals, 44 coal and coal-associated rock samples were collected from the Paleocene and Eocene, Coalmont Formation in the McCallum and Coalmont areas, North Park, Jackson County, Colorado. Twenty-eight samples (24 coal and 4 coal-associated rock) are from the McCallum area and 16 samples (12 coal and 4 coal-associated rock) are from the Coalmont area. Locations of ten core holes and three mines where the samples were collected, and an outline of North Park are shown on figure 1. The 44 samples are briefly described in table 1.

Colorado↗
USGS1981

Proceedings of a workshop on clathrates (gas hydrates) in the National Petroleum Reserve in Alaska, July 16-17, 1979, Menlo Park, California

Purpose : The purpose of this report is to make available the results of the "Workshop on clathrates (gas hydrates) in the National Petroleum Reserve in Alaska," July 16-17, 1979, Menlo Park, California. Scope : Written reports presented by participants of the workshop, relevant letters generated by this workshop and some "forms" created within ONPRA to aid in collecting information are an unusual assemblage but are presented in the proceedings because I feel they can be of use to others. The articles are arranged alphabetically because of the diverse aspects in style and subject matter. A comprehensive list of references was forwarded to Gas Research Institute to avoid duplication of bibliographic effort and because I have been unable to unscramble Russian references to the satisfaction of our editors. The workshop on Clathrates in NPRA : The workshop was convened in Menlo Park on July 16-17, 1979, to review our "knowledge of clathrates and to help develop background for ONPRA 1 s program on clathrates. Speakers were invited to discuss clathrates or some aspect of the physical or chemical relations of clathrates. The letters of invitation, schedule of talks, list of attendees, and a list of workers interested in clathrates are inserted, although the procedure is unusual because these define the scope and objectives of the meetings. Conclusions from the meeting : Conclusions of the discussions are: (a) very little is known about in situ clathrates, (b) our ability to identify in situ clathrates while drilling is poor, (c) the engineering of ONPRA wells is not conductive to the study of clathrates because of the large holes drilled, and (d) ONPRA could justify only limited investigations of clathrates. The attendees unanimously agreed that the next step to be taken by ONPRA should be to examine the wire-line logs and drilling records of NPRA wells to identify probable zones of natural occurring gas hydrates (clathrates). The atttendees stressed the need for more accurate data on natural thermoclines and additional compositional analyses of gases encountered in NPRA wells in order to more accurately define the P/T fields of natural clathrates of NPRA. Article 2 is an overview of results of the meeting.

Alaska↗
USGS1998

Chemical analyses of hot springs, pools, geysers, and surface waters from Yellowstone National Park, Wyoming, and vicinity, 1974-1975

This report presents all analytical determinations for samples collected from Yellowstone National Park and vicinity during 1974 and 1975. Water temperature, pH, Eh, and dissolved O2 were determined on-site. Total alkalinity and F were determined on the day of sample collection. Flame atomic-absorption spectrometry was used to determine concentrations of Li, Na, K, Ca, and Mg. Ultraviolet/visible spectrophotometry was used to determine concentrations of Fe(II), Fe(III), As(III), and As(V). Direct-current plasma-optical-emission spectrometry was used to determine the concentrations of B, Ba, Cd, Cs, Cu, Mn, Ni, Pb, Rb, Sr, and Zn. Two samples collected from Yellowstone Park in June 1974 were used as reference samples for testing the plasma analytical method. Results of these tests demonstrate acceptable precision for all detectable elements. Charge imbalance calculations revealed a small number of samples that may have been subject to measurement errors in pH or alkalinity. These data represent some of the most complete analyses of Yellowstone waters available.

Wyoming↗
USGS1999

Restoration of bighorn sheep metapopulations in and near 15 national parks: Conservation of severely fragmented species; Volume II, Synopsis of research findings

In 1991, the National Park Service (NPS) initiated a series of research studies to support an effort to restore bighorn sheep (Ovis canadensis) into 15 national parks in the Intennountain West and Colorado Plateau areas (Fig. 1). The Biological Resources Division of the U.S. Geological Survey provided scientific advice and research coordination for the NPS restoration (Fig. 2). The research studies were conducted by scientists from the Biological Resources Division of the USGS (fonnerly NBS) (11 research studies), university-based scientists (Univ. of Wyoming- 2 studies, University of Colorado- 1, Colorado State University- 2, University of California, White Mountain Center- 1, Northern Arizona University - 1, Montana State University - 1) and by state agency veterinarians: Drs. Beth Williams of Wyoming, Mike Miller of Colorado, and Terry Spraker of Colorado State University. Only the highlights of these research studies are presented below. Full research reports are available in Volume III of this series.

Colorado, Montana, North Dakota, South Dakota, Uta↗
USGS1999

Digital geologic map of Yellowstone National Park, Idaho, Montana, and Wyoming and vicinity

The geology coverage was developed from the 1972 USGS Geologic Map of Yellowstone National Park. It contains polygons of bedrock formations, dikes, and faults. Errors in the 1972 map were corrected and an area outside the Park boundary on the west and south was added. Attributes attached to each polygon include a formation code, formation name, formation age, and a generalized unit name. Line attributes include water, contacts, and faults. Updated information includes a break down of Tertiary, and Quaternary volcanic rock units.

Idaho, Montana, Wyoming↗
USGS1978

Intrusive rocks northeast of Steamboat Springs, Park Range, Colorado

Major Precambrian and minor Tertiary intrusive rocks northeast of Steamboat Springs in the Park Range between 40°30' and 40°45' N. lat. are described and compared with related rocks elsewhere in Colorado and Wyoming. The Precambrian intrusives were emplaced in a sequence of high-grade interlayered felsic gneisses, amphibolites, and pelitic schists of sedimentary and volcanic origin. These rocks are cut by a major northeast-trending Precambrian shear zone where mainly left lateral movement of 1/ 2 to 1 mile is certain. Cumulative movement of many miles is possible. The Precambrian intrusives consist of a batholith, the Mount Ethel pluton, a smaller Buffalo Pass pluton, and small dikes or lenses of fine-grained porphyry, pegmatites, and ultramafics. The Mount Ethel pluton is an oval shaped body 7 miles wide by about 40 miles long (shown by geophysical data to extend beneath younger sediments in North Park). Outer batholithic contacts are sharp and dip steeply outward at about 85°. Five mappable internal variants consist, in order of decreasing age, of granodiorite, quartz monzonite porphyry of Rocky Peak, quartz monzonite of Roxy Ann Lake, granite and quartz monzonite, and. leucogranite. Internal contacts between these plutonic variants are sharp, and evidence of liquid-solid relationships abounds; despite this, all rocks except the granodiorite contribute to an Rb-Sr whole-rock isochron indicating emplacement about 1.4 b.y. (billion years) ago. The most important variants volumetrically are: the quartz monzonite porphyry of Rocky Peak, which forms an irregular 2-mile-thick carapace or mapped band around the west edge of the pluton and is lithologically similar to nearby Sherman Granite, and the quartz monzonite of Roxy Ann Lake, which forms most of the rest of the pluton and is lithologically similar to Silver Plume Granite. An apparent Sherman -Silver Plume dichotomy with similar rock types and similar relative ages is noted throughout Colorado plutons of that age. The Buffalo Pass pluton consists of the quartz monzonite and gra- nodiorite augen gneiss of Buffalo Mountain and equigranular quartz monzonite gneiss. Internal contacts are not exposed. These rocks contribute to an Rb-Sr whole-rock isochron indicating syntectonic emplacement 1.7-1.8 b.y. ago, essentially the same as the metamorphism of the felsic gneiss wallrocks in the area of this report, and of rocks of Boulder Creek age elsewhere in Colorado. The fine-grained porphyry dikes cut the Buffalo Pass pluton, the ultramafics, and some pegmatites. The dikes are within the age range of the Mount Ethel pluton and are older than the mylonite and shear zones. They occur in both an older northwest-trending and a somewhat younger northeast-trending set but do not appear to change compositionally from one set to the other. Regional considerations indicate that they were emplaced between about 1.1 and 1.5 b.y. ago, a time when intermediate to mafic dikes were commonly emplaced throughout Colorado, Wyoming, and southwestern Montana. The pegmatite and ultramafic bodies are not dated directly, but clustering of many pegmatites outside the contacts of the Mount Ethel pluton may indicate a genetic relation of the pegmatites to the Mount Ethel rocks. Fluorite is a common accessory mineral in the rocks of the Mount Ethel pluton; it has not been observed in this area in the petrographically similar rocks of the Buffalo Pass pluton. Fluorite was precipitated most abundantly from the Precambrian magma that formed the quartz monzonite of Roxy Ann Lake. In 70 percent of these rocks fluorite is observed in amounts as great as 2 percent and is successively less abundant in both older and younger plutonic phases. Textural evidence indicates that, although most fluorite is intergrown with and contemporaneous with other magmatic minerals, some fluorite is associated with alteration minerals in a manner demonstrating its mobility since its initial deposition.

Colorado↗
USGS2000

Environmental geochemical studies of selected mineral deposits in Wrangell-St. Elias National Park and Preserve, Alaska

Environmental geochemical investigations at Wrangell-St. Elias National Park and Preserve, Alaska, between 1994 and 1997 included studies of the Kennecott stratabound copper mines and mill area; historic mines and mill in the Bremner District, gold placer mines at Gold Hill; the undisturbed porphyry, Cu-Mo deposits at Orange Hill and Bond Creek, and the historic mines and mill at Nabesna, The study was in cooperation with the National Park Service and focused on sample media including surface water, bedload sediment, rock, mine waste, and mill tailings samples. Results demonstrate that bedrock geology and mineral deposit type must be considered when environmental geochemical effects of historic or active mine areas are evaluated.

Alaska↗
USGS2008

Geology of the Chesapeake and Ohio Canal National Historical Park and Potomac River Corridor, District of Columbia, Maryland, West Virginia, and Virginia

The Chesapeake and Ohio Canal National Historical Park is 184.5 mi long and extends from Washington, D.C., to Cumberland, Md. The canal passes through three physiographic provinces including the Piedmont, Valley and Ridge, and the Blue Ridge; the map area also includes rocks of the Coastal Plain and Appalachian Plateaus provinces. Each province contains unique packages of rocks that influenced the character of the canal and towpath. The ages of the bedrock encountered along the length of the park range from Mesoproterozoic to Jurassic and represent a variety of tectonic and depositional environments. The different rock types and surficial deposits dictated the various construction methods for the canal, which was excavated in Quaternary flood-plain deposits as well as through bedrock. The ancient course of the Potomac River and the deposits it left behind also influenced the location of the canal and towpath. The engineers made good use of the many rock types to construct the locks, dams, aqueducts, and culverts that guided water from the Potomac River into the canal and maintained the water level as canal boats traveled between higher elevations in western Maryland to sea level in Washington, D.C. The canal and towpath provide a unique transect across the central Appalachian region for examining the rich geologic diversity and history.

District of Columbia, Maryland, West Virginia, Vir↗
USGS2014

Geochronology of plutonic rocks and their tectonic terranes in Glacier Bay National Park and Preserve, southeast Alaska

We have identified six major belts and two nonbelt occurrences of plutonic rocks in Glacier Bay National Park and Preserve and characterized them on the basis of geologic mapping, igneous petrology, geochemistry, and isotopic dating. The six plutonic belts and two other occurrences are, from oldest to youngest: (1) Jurassic (201.6–145.5 Ma) diorite and gabbro of the Lituya belt; (2) Late Jurassic (161.0–145.5 Ma) leucotonalite in Johns Hopkins Inlet; (3) Early Cretaceous (145.5–99.6 Ma) granodiorite and tonalite of the Muir-Chichagof belt; (4) Paleocene tonalite in Johns Hopkins Inlet (65.5–55.8 Ma); (5) Eocene granodiorite of the Sanak-Baranof belt; (6) Eocene and Oligocene (55.8–23.0 Ma) granodiorite, quartz diorite, and granite of the Muir-Fairweather felsic-intermediate belt; (7) Eocene and Oligocene (55.8–23.0 Ma) layered gabbros of the Crillon-La Perouse mafic belt; and (8) Oligocene (33.9–23.0 Ma) quartz monzonite and quartz syenite of the Tkope belt. The rocks are further classified into 17 different combination age-compositional units; some younger belts are superimposed on older ones. Almost all these plutonic rocks are related to Cretaceous and Tertiary subduction events. The six major plutonic belts intrude the three southeast Alaska geographic subregions in Glacier Bay National Park and Preserve, from west to east: (1) the Coastal Islands, (2) the Tarr Inlet Suture Zone (which contains the Border Ranges Fault Zone), and (3) the Central Alexander Archipelago. Each subregion includes rocks assigned to one or more tectonic terranes. The various plutonic belts intrude different terranes in different subregions. In general, the Early Cretaceous plutons intrude rocks of the Alexander and Wrangellia terranes in the Central Alexander Archipelago subregion, and the Paleogene plutons intrude rocks of the Chugach, Alexander, and Wrangellia terranes in the Coastal Islands, Tarr Inlet Suture Zone, and Central Alexander Archipelago subregions.

Alaska↗
USGS2008

Map Showing Limits of Tahoe Glaciation in Sequoia and Kings Canyon National Parks, California

The latest periods of extensive ice cover in the Sierra Nevada include the Tahoe glaciation followed by the Tioga glaciation, and evidence for these ice ages is widespread in the Sequoia and Kings Canyon National Parks area. However, the timing of the advances and retreats of the glaciers during the periods of glaciation continues to be a matter of debate. A compilation of existing work (Clark and others, 2003) defines the Tioga glaciation at 14-25 thousand years ago and splits the Tahoe glaciation into two stages that range from 42-50 and 140-200 thousand years ago. The extent of the Tahoe ice mass shown in the map area is considered to represent the younger Tahoe stage, 42-50 thousand years ago. Evidence of glaciations older than the Tahoe is limited in the southern Sierra Nevada. After the Tioga glaciation, only minor events with considerably less ice cover occurred. The Tioga glaciation was slightly less extensive than the Tahoe glaciation, and each covered about half of the area of Sequoia and Kings Canyon National Parks. The Tahoe glaciers extended 500-1,000 ft lower and 0.5-1.2 mi farther down valleys. Evidence for the Tahoe glacial limits is not as robust as that for Tioga, but the extent of the Tahoe ice is mapped because it covered a larger area and the ice did leave prominent moraines (piles of sediment and boulders deposited by glaciers as they melted at their margins) lower on the east front of the range. Current Sierra redwood (Sequoiadendron giganteum) groves occur in a belt on the west side of the Sierra Nevada, generally west of the area of Tahoe glaciation.

Scientific Investigations Map↗
USGS2009

Geologic Map of the Estes Park 30' x 60' Quadrangle, North-Central Colorado

The rocks and landforms of the Estes Park 30 x 60 minute quadrangle display an exceptionally complete record of geologic history in the northern Front Range of Colorado. The Proterozoic basement rocks exposed in the core of the range preserve evidence of Paleoproterozoic marine sedimentation, volcanism, and regional soft-sediment deformation, followed by regional folding and gradational metamorphism. The metasedimentary rocks of the Estes Park quadrangle are distinct within northern Colorado for preserving the complete metamorphic zonation from low-grade chlorite-muscovite phyllites, through middle greenschist-grade rocks with sequential aluminous porphyroblasts, to partially melted gneisses that contain high-grade cordierite and garnet in the non-melted residues. Regional and textural evidence shows that the widespread metamorphism was essentially concurrent with intrusion of the Boulder Creek Granodiorite and related magmas and with the peak of deformation in the partially melted high-grade rocks. The metamorphic thermal pulse arrived later following the peak of deformation in the physically higher, cooler, low-grade terrane. Mesoproterozoic time was marked by intrusion of biotite granite in the Longs Peak-St Vrain batholith, a complex, irregular body that occupies nearly half of the core of the Front Range in this quadrangle. The magma was dry and viscous as it invaded the metamorphic rocks and caused wholesale plastic folding of the wall rock structure. Steep metamorphic foliation that resulted from the Paleoproterozoic deformations was bowed upward and re-oriented into flat-lying attitudes as the crystal-rich magma rose buoyantly and spread out in the middle crust. Magma invaded the schists and gneisses along weak foliation planes and produced a characteristic sill-upon-sill intrusive fabric, particularly in the higher parts of the batholith. Broad, open arches and swales that are defined by the flow-aligned feldspar foliation of the granite, as well as by compositional banding in the intruded and included metamorphic rocks, formed late during batholith emplacement due to rising, buoyant magma and sinking, dense wall rocks. The Longs Peak-St Vrain batholith was intruded into crust that was structurally neutral or moderately extending in an east-northeast direction. A broad zone of mylonite, the Moose Mountain shear zone, formed within the batholith during the final stages of consolidation as a result of differential buoyancy between the magma and dense wall rock, not as a result of regional tectonic deformation.

Scientific Investigations Map↗
USGS2008

Geologic Map of the Elkhorn Quadrangle, Park County, Colorado

The Elkhorn thrust is defined by the juxtaposition of Early and Middle Proterozoic metamorphic and igneous rocks against Mesozoic and Tertiary rocks. Within the mapped area, an imbricate frontal thrust system juxtaposes Upper Cretaceous rocks against Paleocene rocks of the South Park Formation. In the southeastern section of the quadrangle, Middle Proterozoic igneous rocks are thrust over the South Park Formation. Syntectonic conglomerates (Txc) are preserved both on the hanging wall and footwall of the Elkhorn thrust. North of the map area we have identified normal faulting of probable Quaternary age.

Scientific Investigations Map↗
USGS2011

Geologic map of the Chisos Mountains, Big Bend National Park, Texas

The Chisos Mountains form some of the highest ground in Texas, second only to Guadalupe Peak near the New Mexico border. The northern half of the range is mostly above 5,500 feet with Emory Peak the high point at 7,825 feet. The mountains are centrally located in Big Bend National Park between Panther Junction and Punta de la Sierra. Big Bend National Park lies near the diffuse border between the Great Plains Province to the northeast and the Sonoran section of the Basin-and-Range structural province to the west and southwest. These geologically unique regions are distinguished from one another by large differences in their landscape and by the amount and style of internal structural deformation. The Great Plains Province is characterized by flat-lying or gently dipping sedimentary strata, low topographic relief, shallow stream valleys, and by a general lack of faulting. Very little active deposition is occurring on the plains, except in the bottoms of active stream valleys. In southwestern Texas the plains stand at average elevations of 2,000 to 3,300 feet and slope gently east toward the Mississippi River and the Gulf of Mexico. The Great Plains have remained relatively unchanged for the last 65 million years, except that they have been uplifted to their present height from lower elevations probably in the last 5 million years. The Basin-and-Range province is characterized by linear parallel mountain ranges, deep sediment-filled valleys, and high structural and topographic relief. The eastern part of the province is at a slightly higher average elevation than the plains. The province is known for its complex patterns of Cenozoic faulting. Today it bears little resemblance to the way it was during the Paleocene when the entire Trans-Pecos region was a simple lowland that was near or slightly below sea level.

Scientific Investigations Map↗
USGS2026

Water use permits as of July 2024 and reported water use near the North Unit of Theodore Roosevelt National Park, North Dakota, 1980–2023

Starting in the early 2000s, increasing oil and gas development in western North Dakota created a need for additional water resources from surface-water and groundwater sources near the North Unit of Theodore Roosevelt National Park. To summarize the use of water in that area, the U.S. Geological Survey, in cooperation with the National Park Service, developed a map of surface-water and groundwater resources, aquifers, and water-use diversions, and plotted water-use trends from 1980 to 2023. Reported water used from permits in the map area has more than doubled since 2020, increasing from about 750 acre-feet in 2020 to about 2,300 acre-feet in 2022 and 2,000 acre-feet in 2023. Surface water provided the primary source of reported water used for the study period with an average of about 410 acre-feet per year from 1980 through 2017 and about 1,330 acre-feet per year from 2018 through 2023. After 2011, groundwater sourced from the Little Missouri River, Tobacco Garden Creek, Fox Hills, Fort Union, and Dakota aquifers became a larger portion of total annual reported water use from permits in the map area. From 1980 through 2015, water use for irrigation averaged 86 percent of the total annual reported surface-water and groundwater use in the map area. Starting in 2011, however, industrial uses became a proportionally larger total use of water, and in 2015, became the highest reported volume of water use in the map area. From 2011 to 2023, industrial use designated for water depots increased from 50 acre-feet to about 1,370 acre-feet, accounting for about 70 percent of total reported water use in the map area in 2023.

North Dakota↗
USGS2005

Chemical characteristics of ground-water discharge along the south rim of Grand Canyon in Grand Canyon National Park, Arizona, 2000-2001

Springs flowing from the south rim of Grand Canyon are an important resource of Grand Canyon National Park, offering refuge to endemic and exotic terrestrial wildlife species and maintaining riparian areas. Population growth on the Coconino Plateau has increased the demand for additional development of ground-water resources, and such development could reduce spring discharge and affect the sustainability of riparian areas within the park. In addition, springs are an important source of drinking water for hikers and are culturally and economically important to Native Americans living in the region. Water samples were collected from May 2000 to September 2001 from 20 spring and creek sites that discharge water from the Redwall-Muav Limestone aquifer along the south rim of Grand Canyon. Sample collection sites were described and samples were analyzed for major ions, nutrients, trace elements, radioactivity, and selected isotopes, and potential sources of ground-water flow to the springs. Rock samples representing the major stratigraphic units of Grand Canyon were collected near the Bright Angel Fault and analyzed for mineralogy, strontium-87/strontium-86, and carbon-13/carbon-12. The chemical composition of water samples collected from a given spring did not vary appreciably over the course of the study. Although water at each spring had a temporally constant composition, the composition was chemically distinct from that of every other spring sampled, indicating spatial variability in the ground-water composition. Most samples had a calcium magnesium bicarbonate composition; a few had a substantial sulfate component. Concentrations of arsenic, nitrate, selenium, uranium, and gross alpha approached or exceeded U.S. Environmental Protection Agency Maximum Contaminant Levels in water discharging from some springs. Oxygen and hydrogen isotopic compositions varied little among samples, and for most sites the isotopic data plot close to the global meteoric water line or below the local meteoric water line. Isotopic enrichment indicates fractionation due to evaporation occurs at some sites. The evaporative process may occur prior to recharge or post-discharge. Flow paths are differentiated between the eastern part of the study area where strontium-87/strontium-86 values for water from springs and creeks are more radiogenic than strontium-87/strontium-86 values for water that discharges from sites farther west. Tritium and carbon isotope analyses indicate that residence time of ground-water discharge from springs and creeks ranges from less than 50 years to about 3,400 years. Water with a residence time of less than 50 years is absent at several sites. Discharge of most springs and creeks is a mixture of younger and older waters.

Arizona↗