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At least 109 records · Page 6Linked to original sources

USGS2014

Geologic map of the Ute Mountain 7.5' quadrangle, Taos County, New Mexico, and Conejos and Costilla Counties, Colorado

The Ute Mountain 7.5' quadrangle is located in the south-central part of the San Luis Basin of northern New Mexico, in the Rio Grande del Norte National Monument, and contains deposits that record volcanic, tectonic, and associated alluvial and colluvial processes over the past four million years. Ute Mountain has the distinction of being one of the largest intermediate composition eruptive centers of the Taos Plateau, a largely volcanic tableland occupying the southern portion of the San Luis Basin. Ute Mountain rises to an elevation in excess of 3,000 m, nearly 700 m above the basaltic plateau at its base, and is characterized by three distinct phases of Pliocene eruptive activity recorded in the stratigraphy exposed on the flanks of the mountain and in the Rio Grande gorge. Unconformably overlain by largely flat-lying lava flows of Servilleta Basalt, the area surrounding Ute Mountain records a westward thickening of basin-fill volcanic deposits interstratified in the subsurface with Pliocene basin-fill sedimentary deposits derived from older Tertiary and Precambrian sources to the east. Superimposed on this volcanic stratigraphy are alluvial and colluvial deposits derived from the flanks of Ute Mountain and more distally-derived alluvium from the uplifted Sangre de Cristo Mountains to the east, that record a complex temporal and stratigraphic succession of Quaternary basin deposition and erosion. Pliocene and younger basin deposition was accommodated along predominantly north-trending fault-bounded grabens. These poorly exposed fault scarps cutting lava flows of Ute Mountain volcano. The Servilleta Basalt and younger surficial deposits record largely down-to-east basinward displacement. Faults are identified with varying confidence levels in the map area. Recognizing and mapping faults developed near the surface in young, brittle volcanic rocks is difficult because: (1) they tend to form fractured zones tens of meters wide rather than discrete fault planes, (2) the relative youth of the deposits has resulted in only modest displacements on most faults, and (3) some of the faults may have significant strike-slip components that do not result in large vertical offsets that are readily apparent in offset of sub-horizontal contacts. Those faults characterized as “certain” either have distinct offset of map units or had slip planes that were directly observed in the field. Lineaments defined from magnetic anomalies form an additional constraint on potential fault locations and are indicated as such on the map sheet.

Colorado, New Mexico↗

USGS2018

Geologic map of the Nepenthes Planum Region, Mars

This map product contains a map sheet at 1:1,506,000 scale that shows the geology of the Nepenthes Planum region of Mars, which is located between the cratered highlands that dominate the southern hemisphere and the less-cratered sedimentary plains that dominate the northern hemisphere. The map region contains cone- and mound-shaped landforms as well as lobate materials that are morphologically similar to terrestrial igneous or mud vents and flows. This map is part of an informal series of small-scale (large-area) maps aimed at refining current understanding of the geologic units and structures that make up the highland-to-lowland transition zone. The map base consists of a controlled Thermal Emission Imaging System (THEMIS) daytime infrared image mosaic (100 meters per pixel resolution) supplemented by a Mars Orbiter Laser Altimeter (MOLA) digital elevation model (463 meters per pixel resolution). The map includes a Description of Map Units and a Correlation of Map Units that describes and correlates units identified across the entire map region. The geologic map was assembled using ArcGIS software by Environmental Systems Research Institute ( http://www.esri.com ). The ArcGIS project, geodatabase, base map, and all map components are included online as supplemental data.

Scientific Investigations Map↗

USGS2019

Geologic map of the central-southeast flank of Mauna Loa Volcano, Island of Hawaii, Hawaii

Mauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions began with only brief seismic unrest, while others followed several months to a year of increased seismicity. Once underway, its eruptions can produce lava flows that may reach the sea in less than 24 hours, severing roads and utilities. For example, lava flows erupted from the Southwest Rift Zone (SWRZ) in 1950 advanced at an average rate of 9.3 km per hour, and all three lobes reached the ocean within approximately 24 hours (Finch and Macdonald, 1953). Near the eruptive vents, the flows must have traveled even faster. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa poses an enormous volcanic-hazard threat to the Island of Hawai‘i. Volcanic hazards on Mauna Loa may be anticipated, and risk substantially mitigated, by documenting the past activity to refine our knowledge of the hazards and by alerting the public and local government officials of our findings and their implications for hazards assessments and risk. From the geologic record, we may deduce several generalized facts about the geologic history of the Northeast Rift Zone (NERZ). The middle to uppermost segments of the rift zone were more active in the past 4,000 years than the lower portion of the rift zone. This may be due to buttressing of the lower east rift zone by Mauna Kea and Kīlauea volcanoes. The historical flows that erupted on the north side of the rift zone advanced toward Hilo. This flank of the volcano may be more vulnerable to inundation. Lockwood (1990) noted that the vents of historical activity are migrating to the south. The volcano appears to have a self-regulating mechanism that evenly distributes long-term activity across its flanks. The geologic record also supports this notion; the time prior to the historical period (Age Group 1, pre-A.D. 1832 to 1,000 yrs B.P.; orange units) is dominated by activity on the south side of the NERZ. Although most Mauna Loa eruptions begin in the summit area at the 12,000-ft elevation (Lockwood and Lipman, 1987), the central-southeast flank has not been the source of any activity. All flows originated from the summit or the upper reaches of the Northeast Rift Zone (NERZ) or the Southwest Rift Zone (SWRZ). The NERZ was the source of eight flank eruptions since 1843. The NERZ extends from the 13,680-ft-high summit towards Hilo (population ~60,000; second-largest city in State of Hawaii). The northern portion of the map area is built entirely on flows erupted from the NERZ. The SWRZ extends from the summit towards Kalae (South Point) at sea level. The southern portion of the map area is built entirely on flows erupted from the SWRZ. The map area extends from the 10,350 -ft elevation on Mauna Loa’s east flank toward the Hawaii Volcanoes National Park and the town of Volcano (population approx. 2,000) in the northeast. At the south boundary of the map area is the town of Pāhala (population approx. 900). This map includes areas adjacent to and downslope of the NERZ and regions east of and directly downslope of Moku‘āweoweo, Mauna Loa’s summit caldera. The map encompasses 506 km 2 of the southeast flank (fig. 1) of Mauna Loa from 10,350 -ft elevation to sea level. The map of the central-southeast flank of Mauna Loa shows the distribution and relations of volcanic and surficial sedimentary deposits separated into 15 age groups ranging from a period greater than 50,000 yr B.P. to A.D. 1984. It incorporates previously reported work published in generalized small-scale maps (Lockwood and Lipman, 1987; Lockwood, 1995; Wolfe and Morris, 1996). This map is the second in a series of five maps that will cover Mauna Loa volcano. See SIM 2932-A at https://doi.org/10.3133/sim2932A . NOTE: Map sheet 1 contains lines and type with overprint. This feature may be turned on or off in the Adobe Acrobat page display preferences.

Hawaii↗

USGS2024

Geologic map of the northwest flank of Mauna Loa volcano, Island of Hawai‘i, Hawaii

Mauna Loa, the largest active volcano on Earth, has erupted 34 times since written descriptions became available in A.D. 1832. The most recent eruption of Mauna Loa occurred on November 27, 2022, after a 38 year hiatus; it lasted for 12 days. Some eruptions began with only brief seismic unrest, whereas others followed several months to a year of increased seismicity. Once underway, Mauna Loa’s eruptions can produce lava flows that may reach the sea in less than 24 hours, severing roads and utilities. For example, lava flows that erupted from the Southwest Rift Zone in 1950 advanced at an average rate of 9.3 kilometers per hour (5.8 miles per hour); all three lobes reached the ocean within ~24 hours. Near the eruptive vents, the flows likely traveled even faster. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa has great volcanic-hazard potential for the Island of Hawai‘i. Volcanic hazards on Mauna Loa can be anticipated, and risk substantially mitigated, by documenting its past activity to refine our knowledge of the hazards, and by alerting the public and local government officials of our findings and their implications for hazards assessments and risk. The map of the north and west flanks of Mauna Loa shows the distribution and relation of volcanic and surficial sedimentary deposits. It incorporates previously reported work published as generalized small-scale maps and a more detailed map. Within the mapped area, lava has flowed from three different source regions: the Northeast Rift Zone (22 percent), the summit (64 percent), and radial vents (14 percent). All three have different points of origin which, in turn, affect the flow characteristics and periodicity of activity. The map area includes the uppermost part of the NERZ and extends from the highest elevation––13,040 feet at the south end of the Kokoolau quadrangle, just below the summit caldera––to the sea northwest and west of the summit. Lava that erupts from the north and west flanks typically flows to the west, northwest, or north, depending on the vent location. Both morphologic lava flow types—‘a‘ā and pāhoehoe—are present. Pāhoehoe units tend to spread out or widen in low-slope regions, such as in the saddle regions between Mauna Loa and Mauna Kea or between Mauna Loa and Hualālai. In comparison, ʻaʻā flows generally produce narrower flow lobes that have higher relief. This map is the fifth in a series of five maps that will cover Mauna Loa volcano. NOTE: Map sheet 1 contains lines and type with overprint. This feature may be turned on or off in the Adobe Acrobat page display preferences.

Hawaii↗

USGS1993

Geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington

Since 1979 the Geothermal Research Program of the U.S. Geological Survey has carried out a multidisciplinary research effort in the Cascade Range. The goal of this research is to understand the geology, tectonics, and hydrology of the Cascades in order to characterize and quantify geothermal resource potential. A major goal of the program is compilation of a comprehensive geologic map of the entire Cascade Range that incorporates modern field studies and that has a unified and internally consistent explanation. This map is one of a series presently being compiled that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of lithostratigraphic units; map sheets of the Cascade Range in California and in Oregon complete the series. The complete series forms a guide to exploration and evaluation of the geothermal resources of the Cascade Range and will be useful for studies of volcanic hazards, volcanology, and tectonics. For geothermal reasons, the maps emphasize Quaternary volcanic rocks. Large igneous-related geothermal systems that have high temperatures are associated with Quaternary volcanic fields, and geothermal potential declines rapidly as age increases (Smith and Shaw, 1975). Most high-grade recoverable geothermal energy is likely to be associated with silicic volcanism less than 1 Ma. Lower grade (= lower temperature) geothermal resources may be associated with somewhat older rocks; however, volcanic rocks older than about 2 Ma are unlikely geothermal targets (Smith and Shaw, 1975).

Washington↗

USGS1997

Geology of Point Reyes National Seashore and vicinity, California: A digital database

This Open-File report is a digital geologic map database. This pamphlet serves to introduce and describe the digital data. There is no paper map included in the Open-File report. The report does include, however, a PostScript plot file containing an image of the geologic map sheet with explanation, as well as the accompanying text describing the geology of the area. For those interested in a paper plot of information contained in the database or in obtaining the PostScript plot files, please see the section entitled 'For Those Who Aren't Familiar With Digital Geologic Map Databases' below. This digital map database, compiled from previously published and unpublished data and new mapping by the authors, represents the general distribution of surficial deposits and rock units in Point Reyes and surrounding areas. Together with the accompanying text file (pr-geo.txt or pr-geo.ps), it provides current information on the stratigraphy and structural geology of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:48,000 or smaller.

Open-File Report↗

USGS1997

Quaternary Geology and Liquefaction Susceptibility, San Francisco, California 1:100,000 Quadrangle: A Digital Database

This Open-File report is a digital geologic map database. This pamphlet serves to introduce and describe the digital data. There are no paper maps included in the Open-File report. The report does include, however, PostScript plot files containing the images of the geologic map sheets with explanations, as well as the accompanying text describing the geology of the area. For those interested in a paper plot of information contained in the database or in obtaining the PostScript plot files, please see the section entitled 'For Those Who Aren't Familiar With Digital Geologic Map Databases' below. This digital map database, compiled from previously unpublished data, and new mapping by the authors, represents the general distribution of surficial deposits in the San Francisco bay region. Together with the accompanying text file (sf_geo.txt or sf_geo.pdf), it provides current information on Quaternary geology and liquefaction susceptibility of the San Francisco, California, 1:100,000 quadrangle. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:100,000 or smaller. The content and character of the database, as well as three methods of obtaining the database, are described below.

Open-File Report↗

USGS2009

Preliminary Map of Landslide Deposits in the Mesa Verde National Park Area, Colorado

This report presents a preliminary map of landslide deposits in the Mesa Verde National Park area (see map sheet) at a compilation scale of 1:50,000. Landslide is a general term for landforms produced by a wide variety of gravity-driven mass movements, including various types of flows, slides, topples and falls, and combinations thereof produced by the slow to rapid downslope transport of surficial materials or bedrock. The map depicts more than 200 landslides ranging in size from small (0.01 square miles) earthflows and rock slumps to large (greater than 0.50 square miles) translational slides and complex landslides (Varnes, 1978). This map has been prepared to provide a regional overview of the distribution of landslide deposits in the Mesa Verde area, and as such constitutes an inventory of landslides in the area. The map is suitable for regional planning to identify broad areas where landslide deposits and processes are concentrated. It should not be used as a substitute for detailed site investigations. Specific areas thought to be subject to landslide hazards should be carefully studied before development. Many of the landslides depicted on this map are probably stable as they date to the Pleistocene (approximately 1.8-0.011 Ma) and hence formed under a different climate regime. However, the recognition of these landslides is important because natural and human-induced factors can alter stability. Reduction of lateral support (by excavations or roadcuts), removal of vegetation (by fire or development), or an increase in pore pressure (by heavy rains) may result in the reactivation of landslides or parts of landslides.

Scientific Investigations Map↗

USGS2008

Database for the Geologic Map of Upper Eocene to Holocene Volcanic and Related Rocks of the Cascade Range, Oregon

Since 1979, Earth scientists of the Geothermal Research Program of the U.S. Geological Survey have carried out multidisciplinary research in the Cascade Range. The goal of this research is to understand the geology, tectonics, and hydrology of the Cascades in order to characterize and quantify geothermal resource potential. A major goal of the program is compilation of a comprehensive geologic map of the entire Cascade Range that incorporates modern field studies and that has a unified and internally consistent explanation. This map is one of three in a series that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of rock units distinguished by composition and age; map sheets of the Cascade Range in Washington (Smith, 1993) and California will complete the series. The complete series forms a guide to exploration and evaluation of the geothermal resources of the Cascade Range and will be useful for studies of volcano hazards, volcanology, and tectonics. This digital release contains all the information used to produce the geologic map published as U.S. Geological Survey Geologic Investigations Series I-2569 (Sherrod and Smith, 2000). The main component of this digital release is a geologic map database prepared using ArcInfo GIS. This release also contains files to view or print the geologic map and accompanying descriptive pamphlet from I-2569.

Data Series↗

USGS2002

Geologic map of the Stillwater Complex, Montana: A digital database

This report provides a digital version of the Geologic map of the Stillwater Complex, Montana by Page and Nokleberg (1974). Paper copies of the four geologic map sheets from the original report were scanned and initially attributed by Optronics Specialty Co., Inc. (Northridge, CA) and remitted to the U.S. Geological Survey for further attribution and publication of the geospatial digital files. The resulting digital geologic dataset can be queried in a geographic information system (GIS) in many ways to produce a variety of geological maps.

Montana↗

USGS2020

Geologic map and borehole stratigraphy of Hinkley Valley and vicinity, San Bernardino County, California

Hinkley Valley, in the central to western Mojave Desert of southeastern California, has a long historical record owing to its position as a crossroads for rail and road traffic and its position adjacent to the Mojave River. Subflow in the Mojave River provided groundwater recharge that maintained water consumption and demand by way of shallow wells for local agriculture in the valley. Its crossroads position led to construction of several power-transmission lines, pipeline, and communications cable routes that transect Hinkley Valley. One of these, a natural gas pipeline and its associated compressor station, was the locus of hexavalent chromium, Cr(VI), released into, and consequent contamination of, groundwater. Understanding the movement and fate of the contaminants is a complex hydrologic and geochemical problem. Geologic mapping of the Hinkley Valley area provides framework elements for use in resolving this problem. This report provides new information on surface and subsurface geology to better constrain the origin and geometry of hydrologically important deposits in the Hinkley Valley area and describes youthful faults that may control sediment distribution and groundwater flow. The geologic map (sheet 1) presents substantial new information on surficial geology, including Pliocene deposits, but does not contain significant new work on bedrock. Bedrock investigations were specific to identifying youthful faults and representative outcrops for rocks that were penetrated by boreholes in the valley. Special attention was placed on locating and describing youthful faults. In addition, we analyzed gravity data to (1) map horizontal gradients that we interpret to reflect long-term fault traces and to (2) estimate the depth to bedrock, which is defined as Miocene and older intrusive and metamorphic rocks for the purposes of this report. The subsurface geology of Hinkley Valley was investigated by examining borehole sediment cores and rock encountered at the base of the sediment section. We analyzed the core to determine depositional environments, provenance, and age of the sediment that infilled the valley. Valleys, mountains, and basins in the Hinkley Valley area are topographically complex and incompletely named. The nearly flat floored Hinkley Valley slopes gently northward. It is framed by Mount General and the informally named “Hinkley hills” (southeast of Mount General) on the northeast and by Iron Mountain and Lynx Cat Mountain on the southwest, although breaks in the western mountains allow stream connections between Hinkley Valley and another valley to the west that is herein referred to as Hawes valley. At its south end, Hinkley Valley is traversed by the entrenched Mojave River, which passes east out of the valley past Barstow. North of Hinkley Valley, a few low hills (including Red Hill) separate the valley from a broad west-sloping piedmont that is part of the physiographic Harper Basin (of which the Harper Lake playa is the center). The lower part of this piedmont, however, is referred to as Water Valley, although it is not a distinct valley. The name derives from groundwater sourced from subflow in the Mojave River, which caused shallow water and even artesian flow in Water Valley but not in other parts of the Harper Basin. When water filled the Harper Basin to form Pleistocene Lake Harper it not only submerged Water Valley but also northern Hinkley Valley.

California↗

USGS2019

Geologic map of the Ferncliff and Louisa quadrangles, Louisa, Fluvanna, and Goochland Counties, Virginia

The area encompassed by the geologic map of the Ferncliff and Louisa, Va., 7.5-minute quadrangles includes the hypothetical surface projection of the Quail fault, which is the subsurface fault that was responsible for the 2011 magnitude 5.8 (M5.8) Mineral, Va., earthquake. The mapping shows that the Quail fault appears to have reactivated the Harris Creek fault, a Paleozoic fault that has been mapped and named in the study area and marks the boundary between the Ellisville pluton neck and Chopawamsic Formation. The Harris Creek fault was also reactivated in the early Mesozoic. Another result of the mapping is a well-defined, southwest to northeast, narrow zone of metagraywacke and ultramafic rocks (both part of the informal Shores complex) that marks the closure of a small ocean basin and the accretion of the 468- to 460-Ma (mega-annum) Ordovician Chopawamsic volcanic arc (part of the Carolina terrane) onto Laurentia. The accretion zone is truncated by the Ordovician-Silurian (444 Ma) Ellisville pluton; the 444-Ma age of the pluton therefore represents the minimum age of the accretion zone and indicates likely closure of the ocean basin during the Taconic orogeny. Across the map area, the metamorphic grade ranges from lower-greenschist facies in the northwest to amphibolite facies in the southeast. 40 Ar/ 39 Ar age-dating across this metamorphic gradient indicates that Taconic metamorphism was overprinted by late-Paleozoic Alleghanian metamorphism that was accompanied by refolding and faulting of Taconic structures. Quaternary terraces mapped along the South Anna River record a long history of incision and downcutting. A continuing question is how much of this downcutting was a result of neotectonic uplift in the central Virginia seismic zone. This report consists of a single geologic map sheet and an online geographic information systems database that includes bedrock geologic unit contacts and polygons, surficial geologic polygons, faults, and structural geologic information.

Virginia↗

USGS2004

Topographic Map of the West Candor Chasma Region of Mars, MTM 500k -05/282E OMKT

This map, compiled photogrammetrically from Viking Orbiter stereo image pairs, is part of a series of topographic maps of areas of special scientific interest on Mars. The figure of Mars used for the computation of the map projection is an oblate spheroid (flattening of 1/176.875) with an equatorial radius of 3396.0 km and a polar radius of 3376.8 km. The datum (the 0-km contour line) for elevations is defined as the equipotential surface (gravitational plus rotational) whose average value at the equator is equal to the mean radius as determined by Mars Orbiter Laser Altimeter. The projection is part of a Mars Transverse Mercator (MTM) system with 20? wide zones. For the area covered by this map sheet the central meridian is at 290? E. (70? W.). The scale factor at the central meridian of the zone containing this quadrangle is 0.9960 relative to a nominal scale of 1:500,000. Longitude increases to the east and latitude is planetocentric as allowed by IAU/IAG standards and in accordance with current NASA and USGS standards. A secondary grid (printed in red) has been added to the map as a reference to the west longitude/planetographic latitude system that is also allowed by IAU/IAG standards and has been used for previous Mars maps.

IMAP↗

USGS2004

Topographic map of the Tithonium Chasma Region of Mars, MTM 500k -05/277E OMKT

This map, compiled photogrammetrically from Viking Orbiter stereo image pairs, is part of a series of topographic maps of areas of special scientific interest on Mars. The figure of Mars used for the computation of the map projection is an oblate spheroid (flattening of 1/176.875) with an equatorial radius of 3396.0 km and a polar radius of 3376.8 km. The datum (the 0-km contour line) for elevations is defined as the equipotential surface (gravitational plus rotational) whose average value at the equator is equal to the mean radius as determined by Mars Orbiter Laser Altimeter. The projection is part of a Mars Transverse Mercator (MTM) system with 20? wide zones. For the area covered by this map sheet the central meridian is at 270? E. (70? W.). The scale factor at the central meridian of the zone containing this quadrangle is 0.9960 relative to a nominal scale of 1:500,000. Longitude increases to the east and latitude is planetocentric as allowed by IAU/IAG standards and in accordance with current NASA and USGS standards. A secondary grid (printed in red) has been added to the map as a reference to the west longitude/planetographic latitude system that is also allowed by IAU/IAG standards and has been used for previous Mars maps.

IMAP↗

USGS2004

Topographic Map of the Ophir and Central Candor Chasmata Region of Mars MTM 500k -05/287E OMKT

IMAP↗

USGS2017

Hydrogeologic characteristics and geospatial analysis of water-table changes in the alluvium of the lower Arkansas River Valley, southeastern Colorado, 2002, 2008, and 2015

The U.S. Geological Survey in cooperation with the Lower Arkansas Valley Water Conservancy District measures groundwater levels periodically in about 100 wells completed in the alluvial material of the Arkansas River Valley in Pueblo, Crowley, Otero, Bent, and Prowers Counties in southeastern Colorado, of which 95 are used for the analysis in this report. The purpose of this report is to provide information to water-resource administrators, managers, planners, and users about groundwater characteristics in the alluvium of the lower Arkansas Valley extending roughly 150 miles between Pueblo Reservoir and the Colorado-Kansas State line. This report includes three map sheets showing (1) bedrock altitude at the base of the alluvium of the lower Arkansas Valley; (2) estimated spring-to-spring and fall-to-fall changes in water-table altitude between 2002, 2008, and 2015; and (3) estimated saturated thickness in the alluvium during spring and fall of 2002, 2008, and 2015, and thickness of the alluvium in the lower Arkansas Valley. Water-level changes were analyzed by geospatial interpolation methods. Available data included all water-level measurements made between January 1, 2001, and December 31, 2015; however, only data from fall and spring of 2002, 2008, and 2015 are mapped in this report. To account for the effect of John Martin Reservoir in Bent County, Colorado, lake levels at the reservoir were assigned to points along the approximate shoreline and were included in the water-level dataset. After combining the water-level measurements and lake levels, inverse distance weighting was used to interpolate between points and calculate the altitude of the water table for fall and spring of each year for comparisons. Saturated thickness was calculated by subtracting the bedrock surface from the water-table surface. Thickness of the alluvium was calculated by subtracting the bedrock surface from land surface using a digital elevation model. In order to analyze the response of the alluvium to varying environmental and anthropogenic conditions, the percentage of area of the lower Arkansas Valley showing an absolute change of 3 feet or less was calculated for each of the six water-table altitude change maps. For fall water-table altitude change maps, the periods between 2002 and 2008, 2008 and 2015, and 2002 and 2015 showed that 86.5 percent, 85.2 percent, and 66.3 percent of the study area, respectively, showed a net change of 3 feet or less. In the spring water-table altitude change maps these periods showed a net change of 3 feet or less in 94.4 percent, 96.1 percent, and 90.2 percent of the study area, respectively. While the estimated change in water-table altitude was slightly greater and more variable in fall-to-fall comparisons, these high percentages of area with relatively small net changes indicated that, at least in comparisons of the years presented, there was not a large amount of fluctuation in the altitude of the water table. The saturated thickness in the lower Arkansas Valley was between 25 and 50 feet in 34.4 to 35.9 percent of the study area, depending on the season and year. Between 30.2 and 35.6 percent of the area showed saturated thicknesses between 0 and 25 feet. Less than 1 percent of the area showed a saturated thickness greater than 200 feet in all mapped seasons and years.

Colorado↗

USGS2002

Spatial digital database for the geology of the San Pedro River Basin in Cochise, Gila, Graham, Pima, and Pinal Counties, Arizona

This spatial digital database for the geology of the San Pedro River Basin in southeastern Arizona was compiled from three maps by Dickinson (1993, 1998, 2000). Mylar originals of the map sheets were scanned, and the resultant images were rectified to a mathematically-generated set of latitude and longitude registration points. Geologic linework was digitized from the rectified images on screen using ArcView (ver. 3.2), and the resultant shapefiles were converted to ArcInfo (ver. 7.2) coverages. Lines and polygons were then attributed; and the files were merged omtp a single ArcInfo database (quib24k). This digital spatial database is one of many being created by the U.S. Geological Survey as an ongoing effort to provide geologic information in a geographic information system (GIS) for use in spatial analysis. This database can be queried in many ways to produce a variety of geologic maps. Digital base map data files (topography, roads, towns, rivers and lakes, etc.) are not included: they may be obtained from a variety of commercial and government sources. This database is not meant to be used or displayed at any scale larger than 1:24,000 (for example, 1:12,000). The map area is located in southeastern Arizona. This report describes the map units, the methods used to convert the geologic map data into a digital format, and the ArcInfo GIS file structures and relationships; and it explains how to download the digital files from the U.S. Geological Survey public access World Wide Web site on the Internet. See figures 2 and 3 for page-size versions of the map compilation.

Arizona↗

USGS2017

Geologic map of the northeast flank of Mauna Loa volcano, Island of Hawai'i, Hawaii

Summary Mauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions were preceded by only brief seismic unrest, while others followed several months to a year of increased seismicity. The majority of the eruptions of Mauna Loa began in the summit area (>12,000-ft elevation; Lockwood and Lipman, 1987); yet the Northeast Rift Zone (NERZ) was the source of eight flank eruptions since 1843 (table 1). This zone extends from the 13,680-ft-high summit towards Hilo (population ~60,000), the second largest city in the State of Hawaii. Although most of the source vents are farther than 30 km away, the 1880 flow from one of the vents extends into Hilo, nearly reaching Hilo Bay. The city is built entirely on flows erupted from the NERZ, most older than that erupted in 1843. Once underway, Mauna Loa's eruptions can produce lava flows that reach the sea in less than 24 hours, severing roads and utilities in their path. For example, lava flows erupted from the Southwest Rift Zone (SWRZ) in 1950 advanced at an average rate of 9.3 km per hour, and all three lobes reached the ocean within approximately 24 hours (Finch and Macdonald, 1953). The flows near the eruptive vents must have traveled even faster. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa poses an enormous volcanic-hazard threat to the Island of Hawai‘i. By documenting past activity and by alerting the public and local government officials of our findings, we can anticipate the volcanic hazards and substantially mitigate the risks associated with an eruption of this massive edifice. From the geologic record, we can deduce several generalized facts about the geologic history of the NERZ. The middle to the uppermost section of the rift zone were more active in the past 4,000 years than the lower part, perhaps due to buttressing of the lower east rift zone by Mauna Kea and Kīlauea volcanoes. The historical flows that erupted on the north flank of the rift zone, which is more vulnerable to inundation, advanced toward Hilo. Lockwood (1990) noted that the vents of historical activity are migrating to the south. The volcano appears to have a self-regulating mechanism that evenly distributes long-term activity across its flanks. The geologic record also supports this notion; the time prior to the historical period (Age Group 1, orange units, pre-A.D. 1843–1,000 yr B.P.; see map sheet 2) is dominated by activity on the south side of the NERZ. The NERZ trends N. 65° E. and is about 40 km long and 2–4 km wide, narrowing at the summit caldera. It becomes diffuse (6–7 km wide) at its down-rift terminus, at the approximately 3,400-ft elevation. Its constructional crest is marked by low spatter ramparts and by spatter cones as high as 60 m. Subparallel eruptive fissures and ground cracks cut vent deposits and flows in and near the rift crest. Lava typically flows to the north, east, or south, depending on vent location relative to the rift crest. Encompassing 1,140 km 2 of the northeast flank of Mauna Loa from the 10,880-ft elevation to sea level, the map covers the area from Hilo to Volcano on the east and includes the rift zone from Puu Ulaula quadrangle in the southwest to Hilo in the northeast. The distribution of 105 eruptive units (flows)—separated into 15 age groups ranging from more than 30,000 years B.P. to A.D. 1984—are shown, as well as the relations of volcanic and surficial sedimentary deposits. This map incorporates previously reported work published in generalized small-scale maps (Lockwood and Lipman, 1987; Buchanan-Banks, 1993; Lockwood, 1995; and Wolfe and Morris, 1996).

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