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13 recordsLinked to original sources
USGS1991

Proterozoic geology and ore deposits of Arizona

Proterozoic rocks in Arizona have been the focus of interest for geologists since the late 1800's. Early investigations, led by the U.S. Geological Survey, focused on the extensive ore deposits hosted by Proterozoic rocks. By the 1960's, these studies, combined with theses from academic institutions and the efforts of the Arizona Geological Survey, had produced a rich data base of geologic maps, primarily of the central part of the Transition Zone. The chronological significance of these maps became much better known with the application of U-Pb geochronology by L.Y. Silver and his students starting in the 1960's. The 1970's and early 1980's were marked by numerous contributions from Masters and Ph.D students at a variety of academic institutions, and continued work by the U.S. Geological Survey. Interest in ore deposits persisted and there was an increasing interest in interpretation of the tectonic history of Proterozoic rocks in terms of plate tectonic models, as summarized in papers by Phillip Anderson, Ed DeWitt, Clay Conway, Paul Lindberg, and J.L Anderson in the 1989 Arizona Geological Society Digest 17: "Geologic Evolution of Arizona". The present volume: "Proterozoic Geology and Ore deposits of Arizona" builds upon A.G.S. Digest 17, and presents the results of geologic investigations from the latter part of the 1980's. A number of the papers are condensed versions of MS theses done by students at Northern Arizona University. These papers are based upon 1:10,000 mapping and structural analysis of several areas in Arizona. The geologic maps from each of these studies are available separately as part of the Arizona Geological Survey Contributed Map Series. These detailed maps, plus the continuing mapping efforts of the U.S.G.S. and students at other academic institutions, form an ever improving data base for continuing attempts to understand the Proterozoic geology and ore deposits of Arizona

Book↗
USGS2022

Preliminary bedrock geologic map of the Blythe 30' x 60' quadrangle, California and Arizona

The Blythe 30' x 60' quadrangle in southeastern California and southwestern Arizona displays complex geology that includes Mesozoic contractional deformation, metamorphism, and magmatism in addition to Cenozoic extensional deformation and magmatism. Previous geologic map compilations predate recent geologic mapping efforts that have contributed new insights into the stratigraphy and structure of this quadrangle. This new map, compiled in collaboration with the Arizona Geological Survey, incorporates these recent mapping efforts to provide an updated depiction of the quadrangle’s geologic framework. The scope of this map is limited to bedrock units of Miocene and older age because younger deposits have not been mapped in enough detail across the quadrangle to support a systematic compilation.

Arizona, California↗
USGS2007

Southwest Exotic Mapping Program 2007: Occurrence summary and maps of select invasive, non-native plants in Arizona

An important aspect of management of invasive, non-native plants (invasive plants) is information on the type, location, and magnitude of infestations. Regional development of this information requires an integrated program of data collection, management, and delivery. The Southwest Exotic Plant Mapping Program (SWEMP), coordinated through the U.S. Geological Survey’s Southwest Biological Science Center, annually compiles occurrence records for infestations of invasive plants. Operating since 1998, the SWEMP team has accepted occurrence records contributed voluntarily by federal, tribal, state, and private collaborators and has compiled these contributions accumulatively with previous versions of SWEMP. The SWEMP 2007 regional database update, SWEMP07, contains 62,000 records for 221 plant species with records dating as far back as 1911 and up to December, 2006. Records include invasive plants in Arizona, eastern California, Colorado, New Mexico, and Utah. SWEMP07 is available through the Southwest Exotic Plant Information Clearinghouse ( http://sbsc.wr.usgs.gov/research/projects/swepic/swepic.asp , click SWEMP). Not all invasive plants are non-native and not all invasive plants are even invasive. The Arizona Invasive Species Advisory Council (2006) defined an invasive species as “a species that is (1) non-native to the ecosystem under consideration and, (2) whose introduction causes or is likely to cause economic or environmental harm, or harm to human health”. SWEMP uses the U.S. Department of Agriculture PLANTS database ( http://plants.usda.gov/ ) to determine if a plant is native or not to Arizona. As SWEMP does not independently assess the current or potential impact of invasive plants, we include most non-native plant records contributed. We have not included agricultural crops that are non-native, for example apples, oranges, etc. In this open-file-report, we use the SWEMP07 update to summarize the occurrence of invasive plants in Arizona and present distribution maps for a select invasive plants in Arizona. We use the word occurrence purposefully instead of the word distribution. The SWEMP07 database only provides an estimate of the actual distribution of invasive plants in Arizona. The information provided is a first approximation of the state-wide extent of invasive plant distribution.

Open-File Report↗
USGS2000

Data for Quaternary faults in western Montana

The "World Map of Major Active Faults" Task Group is compiling published fault data, developing a digital database of the fault data, and preparing a series of maps for the United States and other countries in the western Hemisphere. The data is intended to portray the locations, ages, and activity rates of major earthquake-related features such as faults, folds, and liquefaction features that have geologic evidence of Quaternary (1.6 Ma) deformation. The Western Hemisphere effort is sponsored by International Lithosphere Program (ILP) Task Group II-2; the data compilation, database, and map for the United States is funded largely by the National Earthquake Hazard Reduction Program (NEHRP) through the U.S. Geological Survey. The ILP effort in the Western Hemisphere is coordinated by Michael N. Machette, the digital database is designed and managed Kathleen M. Haller, and map data are digitized and manipulated by Richard L. Dart. In addition to meeting the goals of the Task Group II-2, this effort represents a key contribution to the new Global Seismic Hazards Assessment Program (ILP Task Group II-0) for the International Decade for Natural Disaster Reduction. This compilation, which documents the published data on Quaternary surface faulting in western Montana, is one of many similar state or regional compilations that are planned for the project. Compilations for Arizona (Pearthree, 1998 #2945), Colorado (Widmann and others, 1998 #3441), New Mexico (Machette and others, 1998), and West Texas (Collins and others, 1996 #993) are currently available and the compilation for features east of the Rocky Mountain front will be available in early 2000 (Crone and Wheeler, in press). All are primarily a catalog of data that includes a variety of geographic, geologic, and paleoseismologic parameters for known or assumed Quaternary faults. These data compilations, the digital database, and the companion maps summarize the published information on known tectonic features and present the information in an internally consistent format. The compilations will be available in digital database format on the WorldWide Web in the near future, which will greatly improve their utility. Release of data for individual states and regions within the United States in this text-based format was necessary because of the time required to develop the national database.

Montana↗
USGS1978

The Energy Lands Program of the U.S. Geological Survey, fiscal year 1976

The Energy Lands Program of the U.S. Geological Survey comprises several projects that conduct basic and interpretive earth-science investigations into the environmental aspects of energy-resource recovery, transmission, and conversion. More than half the coal reserves of the United States occur west of the Mississippi River; therefore, the program concentrates mostly on coal-producing regions in the Western interior. Additional studies involve the oil-shale region in Colorado, Wyoming, and Utah, and coal-related work in Alaska and Appalachia. The work is done both by USGS personnel and under USGS grants and contracts through the Energy Lands Program to universities, State Geological Surveys, and private individuals. Maps and reports characterizing many aspects of environmental earth science are being prepared for areas of Alaska, Montana, North Dakota, Wyoming, Utah, Colorado, New Mexico, Arizona, Oklahoma, Kansas, and Texas. Types of studies underway include bedrock, surficial, and interpretive geology; engineering geology, geochemistry of surface materials and plants; climatic conditions as they influence rehabilitation potential of mined lands; and feasibility of surface vs. underground mining. The purpose common to all investigations in the Energy Lands Program is to provide timely earth-science information for use by managers, policy-makers, engineers, scientists, planners, and others, in order to contribute to an environmentally sound, orderly, and safe development of the energy resources of the Nation.

Circular↗
USGS1969

The Geologic Story of the Uinta Mountains

The opening of the West after the Civil War greatly stimulated early geologic exploration west of the 100th Meridian. One of the areas first studied, the Uinta Mountains region, gained wide attention as a result of the explorations of three Territorial Surveys, one headed by John Wesley Powell, one by Clarence King, and one by Ferdinand V. Hayden. Completion of the Union Pacific Railroad across southern Wyoming 100 years ago, in 1869, materially assisted geologic exploration, and the railheads at Green River and Rock Springs greatly simplified the outfitting of expeditions into the mountains. The overlap of the Powell, King, and Hayden surveys in the Uinta Mountains led to efforts that were less concerted than competitive and not without acrimony. Many parts of the area were seen by all three parties at almost the same time. Duplication was inevitable, of course, but all three surveys contributed vast quantities of new knowledge to the storehouse of geology, and many now-basic concepts arose from their observations. Powell's area of interest extended mainly southward from the Uinta Mountains to the Grand Canyon, including the boundless plateaus and canyons of southern Utah and northern Arizona. King's survey extended eastward from the High Sierra in California to Cheyenne, Wyoming, and encompassed a swath of country more than 100 miles wide. Hayden's explorations covered an immense region of mountains and basins from Yellowstone Park in Wyoming southeast throughout most of Colorado. Powell first entered the Uinta Mountains in the fall of 1868, having traveled north around the east end of the range from the White River country to Green River, Wyoming, then south over a circuitous route to Flaming Gorge and Browns Park, and finally back to the White River, where he spent the winter. In 1869, after reexamining much of the area visited the previous season, Powell embarked on his famous 'first boat trip' down the Green and Colorado Rivers. This trip was more exploratory than scientific; his second, more scientific trip was made 2 years later. Powell revisited the Uinta Mountains in 1874 and 1875 to complete the studies begun 6 years earlier. His classic 'Report on the Geology of the Eastern Portion of the Uinta Mountains and a Region of Country Adjacent Thereto' was published in 1876. King's survey?officially 'The United States Geological Exploration of the Fortieth Parallel'?is better known simply as the '40th Parallel Survey.' King began working eastward from California in 1867. The Uinta Mountains region, however, was mapped by S. F. Emmons, under the supervision of King, in the summers of 1869 and 1871. Emmons' work was monumental, and although he emphasized in his letter of transmittal to King the exploratory nature of the work?as the formal title of the report indicates?his maps, descriptions, and conclusions reflect a comprehensive understanding of the country and its rocks. The 40th Parallel report contains the best, most complete early descriptions of the Uinta Mountains. It, indeed, is a treasurechest of information and a landmark contribution to the emerging science of geology. Hayden visited the Uinta Mountains in 1870, descending the valley of Henrys Fork to Flaming Gorge in the fall after having earlier examined the higher part of the range to the west. Most of Hayden's observations were cursory, and he repeatedly expressed regret at having insufficient time for more detailed studies. In reference to the area between Clay Basin and Browns Park, he remarked (Hayden, 1871, p. 67) somewhat dryly that 'the geology of this portion of the Uinta range is very complicated and interesting. To have solved the problem to my entire satisfaction would have required a week or two.' Eighty-odd years later I spent several months there?looking at the same rocks. Powell was perhaps more creative?more intuitive?than either King or Hayden, and his breadth of interest in the fields of geology, physiography, ethnology, an

Bulletin↗
USGS2007

Map and data for Quaternary faults and fault systems on the Island of Hawai'i

Introduction This report and digitally prepared, GIS-based map is one of a series of similar products covering individual states or regions of United States that show the locations, ages, and activity rates of major earthquake-related features such as faults and fault-related folds. It is part of a continuing the effort to compile a comprehensive Quaternary fault and fold map and database for the United States, which is supported by the U.S. Geological Survey's (USGS) Earthquake Hazards Program. Guidelines for the compilation of the Quaternary fault and fold maps for the United States were published by Haller and others (1993) at the onset of this project. This compilation of Quaternary surface faulting and folding in Hawai`i is one of several similar state and regional compilations that were planned for the United States. Reports published to date include West Texas (Collins and others, 1996), New Mexico (Machette and others, 1998), Arizona (Pearthree, 1998), Colorado (Widmann and others, 1998), Montana (Stickney and others, 2000), Idaho (Haller and others, 2005), and Washington (Lidke and others, 2003). Reports for other states such as California and Alaska are still in preparation. The primary intention of this compilation is to aid in seismic-hazard evaluations. The report contains detailed information on the location and style of faulting, the time of most recent movement, and assigns each feature to a slip-rate category (as a proxy for fault activity). It also contains the name and affiliation of the compiler, date of compilation, geographic and other paleoseismologic parameters, as well as an extensive set of references for each feature. The map (plate 1) shows faults, volcanic rift zones, and lineaments that show evidence of Quaternary surface movement related to faulting, including data on the time of most recent movement, sense of movement, slip rate, and continuity of surface expression. This compilation is presented as a digitally prepared map product and catalog of data, both in Adobe Acrobat PDF format. The senior authors (Eric C. Cannon and Roland Burgmann) compiled the fault data as part of ongoing studies of active faulting on the Island of Hawai`i. The USGS is responsible for organizing and integrating the State or regional products under their National Seismic Hazard Mapping project, including the coordination and oversight of contributions from individuals and groups (Michael N. Machette and Anthony J. Crone), database design and management (Kathleen M. Haller), and digitization and analysis of map data (Richard L. Dart). After being released an Open-File Report, the data in this report will be available online at http://earthquake.usgs.gov/regional/qfaults/, the USGS Quaternary Fault and Fold Database of the United States.

Hawaii↗
USGS2006

Mapping ground water in three dimensions: An analysis of airborne geophysical surveys of the Upper San Pedro River Basin, Cochise County, southeastern Arizona

This report summarizes the results of two airborne geophysical surveys conducted in the upper San Pedro Valley of southeastern Arizona in 1997 and 1999. The combined surveys cover about 1,000 square kilometers and extend from the Huachuca Mountains on the west to the Mule Mountains and Tombstone Hills on the east and from north of the Babocomari River to near the Mexican border on the south. The surveys included the acquisition of high-resolution magnetic data, which were used to map depth to the crystalline basement rocks underlying the sediments filling the basin. The magnetic inversion results show a complex basement morphology, with sediment thickness in the center of the valley ranging from ~237 meters beneath the city of Sierra Vista to ~1,500 meters beneath Huachuca City and the Palominas area near the Mexican border. The surveys also included acquisition of 60-channel time-domain electromagnetic (EM) data. Extensive quality analyses of these data, including inversion to conductivity vs. depth (conductivity-depth-transform or CDT) profiles and comparisons with electrical well logs, show that the electrical conductor mapped represents the subsurface water-bearing sediments throughout most of the basin. In a few places (notably the mouth of Huachuca Canyon), the reported water table lies above where the electrical conductor places it. These exceptions appear to be due to a combination of outdated water-table information, significant horizontal displacement between the wells and the CDT profiles, and a subtle calibration issue with the CDT algorithm apparent only in areas of highly resistive (very dry) overburden. These occasional disparities appear in less than 5 percent of the surveyed area. Observations show, however, that wells drilled in the thick unsaturated zone along the Huachuca Mountain front eventually intersect water, at which point the water rapidly rises high into the unsaturated zone within the wellbore. This rising of water in a wellbore implies some sort of confinement below the thick unsaturated zone, a confinement that is not identified in the available literature. Occasional disparities notwithstanding, maps of the electrical conductor derived from the airborne EM system provide a synoptic view of the presence of water underlying the upper San Pedro Valley, including its three-dimensional distribution. The EM data even show faults previously only inferred from geologic mapping. The magnetic and electromagnetic data together appear to show the thickness of the sediments, the water in the saturated sediments down to a maximum of about 400 meters depth, and even places where the main ground-water body is not in direct contact with the San Pedro River. However, the geophysical data cannot reveal anything directly about hydraulic conductivity or ground-water flow. Estimating these characteristics requires new hydraulic modeling based in part on this report. One concern to reviewers of this report is the effect that clays may have on the electrical conductor mapped with the airborne geophysical system. Although the water in the basin is unusually conductive, averaging 338 microsiemens per centimeter, reasoning cited below suggests that the contribution of clays to the overall conductivity would be relatively small. Basic principles of sedimentary geology suggest that silts and clays should dominate the center of the basin, while sands and gravels would tend to dominate the margins. Although clay content may increase the amplitude of the observed electrical conductors somewhat, it will not affect the depths to the conductor derived from depth inversions. Further, fine-grained sediments generally have higher porosity and tend to lie toward a basin center, a fact in general agreement with the observed geophysical data.

Arizona↗
USGS2024

Ground deformation and gravity for volcano monitoring

Introduction When magma accumulates or migrates, it can cause pressurization and related ground deformation. Characterization of surface deformation provides important constraints on the potential for future volcanic activity, especially in combination with seismic activity, gas emissions, and other indicators. A wide variety of techniques and instrument types have been applied to the study of ground deformation at volcanoes (sidebar, p. 2; Dzurisin, 2000, 2003, 2007). Geodetic instruments include continuously recording Global Navigation Satellite System (GNSS; of which the United States’ Global Positioning System is one example) stations (fig. D1), borehole tiltmeters, and interferometric synthetic aperture radar (InSAR) measurements (from satellites, occupied and unoccupied aircraft systems, and ground-based sensors). Additional geodetic measurements like continuous- and survey-mode gravity (fig. D2) can contribute substantially to interpreting these data. Borehole strainmeters (see chapter K , this volume, by Hurwitz and Lowenstern, 2024) also have outstanding utility for monitoring deformation, although because of cost and permitting challenges, we do not include them as part of standard volcano monitoring networks for U.S. volcanoes. Still other techniques like light detection and ranging (lidar), structure from motion, and optical satellite data can be used to derive gross topographic changes, which can be used to map volcanic deposits, infer eruption rates, and gain insights into the source processes associated with eruptive activity (see chapter G , this volume, on tracking surface changes caused by volcanic activity; Orr and others, 2024). Experience has shown that no single geodetic monitoring technique is adequate to detect and track the entire range of ground-motion patterns that occur at volcanoes, primarily because of the temporal and spatial diversity of volcano deformation (fig. D3). Similarly, the magnitude of surface deformation varies widely. Geodetic monitoring strategies should therefore include multiple techniques and instrument types to cover a wide range of spatial and temporal scales. In identifying recommendations for geodetic instrumentation for volcano monitoring networks, we attempted to maximize the diversity of instrument types to measure the full range of deformation signals and minimize their expense and number; thus, we do not include several well-known deformation-monitoring techniques in our recommendations. Extensometers, for example, measure strains over distances of a few meters and have an excellent record of success in detecting changes in preeruptive localized ground motion across existing cracks, including at Mount St. Helens, Washington (Iwatsubo and others, 1992), and Piton de la Fournaise, Réunion Island (Peltier and others, 2006). Despite being relatively inexpensive, extensometers are best used primarily when localized ground displacements (for example, ground cracks) need to be tracked, and are not necessary at all volcanoes. In considering volcano deformation monitoring strategies, two complicating factors are deserving of special attention. First, not all deformation is driven by subsurface magmatic activity—for example, at many large stratovolcanoes (for example, Mount Rainier), flank collapses and landslides are significant geologic hazards (Reid and others, 2001) that may occur even in the absence of magmatic activity. Monitoring the stability of volcanoes is thus another critical application of geodetic monitoring networks to inform hazard assessment. One of the most famous examples of edifice instability is the large flank collapse that initiated the May 18, 1980, eruption of Mount St. Helens. Deformation monitoring had detected a bulge on the north flank of the mountain in April 1980 that was expanding by several meters per day (Lipman and others, 1981). Given that flank collapses can happen at any time during a period of volcanic unrest (or even outside a period of unrest), the capability to assess edifice stability is critical. Second, although volcanoes are commonly treated as idealized structures that erupt from single points, like centralvent stratovolcanoes, many are characterized by long rift zones from which eruptions may originate, and distributed volcanic fields are characterized by broadly spaced vents. For example, linear dikes are common at Kīlauea, Mauna Loa, and between Mount Shasta and Medicine Lake in California. At Kīlauea, one of these linear dikes emerged more than 40 kilometers (km) away from the summit of the volcano during the lower East Rift Zone eruption in 2018. Other volcanic fields, like Lassen volcanic center, California, or the San Francisco Volcanic Field, Arizona, have many small vents spread over a wide area. Although the instrumentation guidelines presented in this chapter remain phrased for central-vent volcanoes, they should be modified as needed in the context of the eruptive characteristics of each individual volcanic system. Spatial analysis of geodetic network coverage could help to ensure adequate instrumentation in areas where volcanism can occur over a broad area as opposed to a central vent. As an example, consider the adjacent volcanoes Mount Shasta and Medicine Lake. If station locations are chosen based only on the distance from the centers of the volcanoes, then any geodetic anomalies between the two volcanoes—an area of potential volcanism as indicated by the presence of volcanic features—may remain undetected by ground-based instrumentation. The spatial analysis is accomplished via a grid of pressure point sources (Mogi, 1958) evenly distributed across the map area, at a depth of 5 km in this example (fig. D4). Each source is inflated until predicted deformations exceed the GNSS white noise uncertainty estimates at one site (Langbein, 2017; Murray and Svarc, 2017). This volume of detectable magma provides a measure of the quality of the coverage (fig. D4). The results indicate that, as of 2022, there is a large area between Mount Shasta and Medicine Lake volcano with existing mapped dikes in which a substantial amount of magma could intrude without being detected geodetically. Applying this style of analysis to individual volcanic systems can provide a guide for designing network geometry given the expected locations of future eruptions.

Scientific Investigations Report↗
USGS1952

Ground water in the Gila River Basin and adjacent areas, Arizona: a summary

This report is a resume' of the principal facts collected by the Geological Survey in the period 1890-1952 about the ground-water resources of the Gila River basin and certain other areas in Arizona. Since 1939 the Geological Survey has been making ground-water investigations on a continuing basis in cooperation with the State of Arizona. Since 1940 the cooperating agency has been the State Land Department. The occurrence of ground water in fifteen areas that form a part of the Gila River drainage basin is described in this report. The areas are denoted by the name of a town or geographic feature, and are as follows: Duncan, Safford, San Simon, Upper San Pedro, Lower San Pedro, Aravaipa Creek, Upper Santa Cruz, Lower Santa Cruz, Salt River Valley, Rainbow ValleyWaterman Wash, McMullen Valley, Harquahala Plain, Gila Bend, Palomas Plain, and Wellton-Mohawk. Data also are presented for several areas not in the Gila River system, including Ranegras Plain and the Willcox and Douglas basins. A summary of the data is given following the ground-water discussion in each area. A series of maps accompany the report, including an index map and maps of the principal areas of ground-water development. The mar,z, show the geology, the location of most of the irrigation wells and irrigated lands, and, where data were available, contours of the water table, depth to the water table, and changes in its position over a period of years. Ground water occurs in the region primarily in alluvial fill consisting of gravel, sand, silt, and clay which was deposited in structural troughs between mountain ranges. Ground water stored in these alluvial basins is derived from many sources. The principal sources are infiltration from runoff along the mountain fronts and seepage from irrigation water applied to cultivated lands. Of great interest in Arizona at the present time is the rate of depletion of ground-water reserves by withdrawals from storage. Use of ground water in Arizona increased by more than 50 percent in the 6-year period 1'46-51, from 2,400,000 acre-feet in 1946 to 3,750,000 acre-feet in 1951. The areas of greatest withdrawal are in Pinal and Maricopa Counties, in the southcentral part of the State. Maps and hydrographs accompanying this report show that the water table is declining in the heavily pumped areas, indicating that ground water is being withdrawn in excess of replenishment. The rate of decline has been as much as 10 feet per year in the most intensively pumped areas, and has been greatest during the past few years. In an effort to compensate for decreased well yields resulting from the decline of the water table in some areas, many deep wells have been drilled within the past few years. The deep aquifers do not represent a new source of water; their water is a part of the common supply of the structural basins in which they lie. The aquifers tapped by these deep wells generally yield less water per foot of drawdown than the shallower aquifers. The water in the deeper aquifers is variable in quality, ranging from water too high in dissolved solids to be usable for irrigation to water lower in concentration than that in the overlying aquifers. The quality of the ground waters in most of the region is considered suitable for irrigation. In local areas, however, the ground waters are naturally unsuitable for irrigation and, in other areas, the concentration of dissolved solids has increased sufficiently to make the waters harmful to some crops. The problem of salt balance is becoming increasingly important, not only in the Salt River Valley area, but also in other parts of the Gila River Basin. A discussion of the salt-balance problem is given in Part II of this report. It should be emphasized that ground waters in each of the individual areas in the Gila River drainage system are interrelated with ground waters in adjacent areas upstream and downstream. The connection is tenuous between some areas, but in central Arizona the ground waters in the different areas are closely related. Although subsurface barriers to ground-water movement exist in places, they are not everywhere fully effective. The ground-water--surface-water interrelationship is important in some areas. Those basins occupied by perennial streams, or by streams having large influent seepage losses, have not shown large, perennial declines of water levels in wells. Effluent seepage of ground water contributes to stream flow in the lower reaches of several basins.

Arizona↗
USGS2006

Hydrogeologic framework refinement, ground-water flow and storage, water-chemistry analyses, and water-budget components of the Yuma area, southwestern Arizona and southeastern California

The ground-water and surface-water system in the Yuma area in southwestern Arizona and southeastern California is managed intensely to meet water-delivery requirements of customers in the United States, to manage high ground-water levels in the valleys, and to maintain treaty-mandated water-quality and quantity requirements of Mexico. The following components in this report, which were identified to be useful in the development of a ground-water management model, are: (1) refinement of the hydrogeologic framework; (2) updated water-level maps, general ground-water flow patterns, and an estimate of the amount of ground water stored in the mound under Yuma Mesa; (3) review and documentation of the ground-water budget calculated by the Bureau of Reclamation, U.S. Department of the Interior (Reclamation); and (4) water-chemistry characterization to identify the spatial distribution of water quality, information on sources and ages of ground water, and information about the productive-interval depths of the aquifer. A refined three-dimensional digital hydrogeologic framework model includes the following hydrogeologic units from bottom to top: (1) the effective hydrologic basement of the basin aquifer, which includes the Pliocene Bouse Formation, Tertiary volcanic and sedimentary rocks, and pre-Tertiary metamorphic and plutonic rocks; (2) undifferentiated lower units to represent the Pliocene transition zone and wedge zone; (3) coarse-gravel unit; (4) lower, middle, and upper basin fill to represent the upper, fine-grained zone between the top of the coarse-gravel unit and the land surface; and (5) clay A and clay B. Data for the refined model includes digital elevation models, borehole lithology data, geophysical data, and structural data to represent the geometry of the hydrogeologic units. The top surface of the coarse-gravel unit, defined by using borehole and geophysical data, varies similarly to terraces resulting from the down cutting of the Colorado River. Clay A is nearly the same as the previous conceptual hydrogeologic model definition (Olmsted and others, 1973), except for a minor westward extension from the city of Yuma. Clay B is extended to the southerly international boundary and increased in areal extent by about two-thirds of the original extent (Olmsted and others, 1973). The other hydrogeologic units generally are the same as in the previous conceptual hydrogeologic model. Before development, the Colorado and Gila Rivers were the sources of nearly all the ground water in the Yuma area through direct infiltration of water from river channels and annual overbank flooding. After construction of upstream reservoirs and clearing and irrigation of the floodplains, the rivers now act as drains for the ground water. Ground-water levels in most of the Yuma area are higher now than they were in predevelopment time. A general gradient of ground-water flow toward the natural discharge area south of the Yuma area still exists, but many other changes in flow are evident. Ground water in Yuma Valley once flowed away from the Colorado River, but now has a component of flow towards the river and Mexicali Valley. A ground-water mound has formed under Yuma Mesa from long-term surface-water irrigation; about 600,000 to 800,000 acre-ft of water are stored in the mound. Ground-water withdrawals adjacent to the southerly international boundary have resulted in water-level declines in that area. The reviewed and documented water budget includes the following components: (1) recharge in irrigated areas, (2) evapotranspiration by irrigated crops and phreatophytes, (3) ground-water return flow to the Colorado River, and (4) ground-water withdrawals (including those in Mexicali Valley). Recharge components were calculated by subtracting the amount of water used by crops from the amount of water delivered. Evapotranspiration rates were calculated on the basis of established methods, thus were appropriate for input to the ground-water flow model developed by the Bureau of Reclamation (William Greer, hydrologist, Bureau of Reclamation, written commun., 2005). Evapotranspiration by crops and phreatophytes were calculated by using crop coefficient methods and meteorological data. Other methods of calculating evapotranspiration rates by using combinations of satellite imagery and ground-based data could be used for higher spatial and temporal resolution. Ground-water return flow during years of low flow on the Colorado River (1972–82, 1987–92, and 1994–96) averaged 79,000 acre-ft per year. Ground-water withdrawal data for 1970–99 were similar to other estimates made by the U.S. Geological Survey for the Yuma area. New water-chemistry data were collected in 12 wells and 8 canals/drains to characterize spatial patterns in chemical constituents, determine isotopic ages of water, infer possible sources of ground water, and locate the vertical intervals of the aquifer that contribute most water to wells. Depth-dependent samples were collected at one of the wells (YM-10). A large quantity of water-quality data were compiled from Bureau of Reclamation and U.S. Geological Survey records and merged into the U.S. Geological Survey National Water Information System database. New samples were analyzed for major ions, nutrients, stable isotopes of oxygen and hydrogen, tritium ( 3 H), and carbon-14 ( 14 C) (along with C 13 /C 12 ratios). Light values of oxygen-18 ( 18 O) and deuterium ( 2 H, D) in well 242-2 indicate recharge from the Colorado River. Heavy water samples from wells 242-22, CADC, and Mesa del Sol indicate local recharge sources. Tritium data indicate there is young water in wells in the valleys and near the edge of Yuma Mesa, while older water is found far from the Colorado River. 14 C data indicate that water from wells near the southerly international boundary is at least several thousand years old.

Arizona, California↗