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At least 1,153 records · Page 64Linked to original sources
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 This map is one of a series presently being compiled that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of lithostratigraphic units; map sheets of the Cascade Range in California and in Oregon complete the series.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↗
USGS1994

Geologic map of the eastern part of the Challis National Forest and vicinity, Idaho

The paper version of the Geologic Map of the eastern part of the Challis National Forest and vicinity, Idaho was compiled by Anna Wilson and Betty Skipp in 1994. The geology was compiled on a 1:250,000 scale topographic base map. TechniGraphic System, Inc. of Fort Collins Colorado digitized this map under contract for N.Shock. G.Green edited and prepared the digital version for publication as a GIS database. The digital geologic map database can be queried in many ways to produce a variety of geologic maps.

IMAP↗
USGS2002

Geologic and isostatic gravity map of the Nenana basin area, central Alaska

The Nenana Basin area is a prospective petroleum province in central Alaska, and this geologic and isostatic gravity map is part of a petroleum resource assessment of the area. The geology was compiled from published sources as shown on the index map (map sheet). Map units are organized and presented according to the scheme of lithotectonic terranes proposed by Jones and others (1987) and Silberling and Jones (1984); we recognize, however, that this terrane scheme is controversial and likely to be revised in the future. In some cases, we combined certain terranes because we were unable to match the terrane boundaries given by Jones and others (1987) and Silberling and Jones (1984) with specific faults shown on existing geologic maps. Postaccretion cover deposits represent overlap assemblages that depositionally overlie accreted terranes. Plutonic igneous rocks shown on this map include several plutons that are clearly postaccretionary, based on isotopic ages and (or) field relations. It is possible that some of the plutons predate accretion, but this has not been demonstrated. According to Jones and others (1982), the terranes in the area of our map were assembled during late Mesozoic or earliest Cenozoic time. The gravity contours are derived from data used in earlier compilations that are supplemented by some National Oceanic and Atmospheric Administration data along the Alaska Pipeline level line. The earlier compilations were used for simple Bouguer maps, prepared primarily by non-digital methods, and are superseded by this map. The present map is the result of digital processing that includes the 1967 Geodetic Reference System, the IGSN-71 datum, digital terrain corrections, and conversion to isostatic gravity so that geologic structures on the margin of the Alaska Range are more clearly portrayed. Computation procedures are described in part by Barnes (1972, 1984), Jachens and Roberts (1981), and Barnes and others (1994). The calculations used a crustal density of 2.67 g/cm 3 , a density contrast at the base of the isostatic root of 0.4 g/cm 3 , and a root thickness at sea level of 25 km. The distribution of data within the map area is uneven and locally controls the shape of the computer-generated contours. Altimetry was used for most of the elevation control and its inconsistency is responsible for many of the small contour irregularities. Ninety percent of the measurements are estimated to have an accuracy of about 1.5 mgal or about a quarter of the 5 mgal contour interval. Data collection and analysis were assisted by R.V. Allen, R.C. Jachens, M.A. Fisher, T.R. Bruns, J.G. Blank, J.W. Bader, Z.C. Valin, J.W. Cady, R.L. Morin, and P.V. Woodward. The most promising area for petroleum exploration is a prominent 25 mgal isostatic gravity low north of Nenana (T. 2 S., R. 8 W.). This gravity low probably corresponds to the deepest part of a sedimentary basin filled by Cenozoic strata that includes nonmarine fluvial and lacustrine deposits of the Eocene to Miocene Usibelli Group. Smaller gravity lows are associated with outcrops of these sedimentary rocks north of Suntrana (T. 12 S., R. 6-9 W.) and Sable Pass (T. 16 S., R. 11 W.). A broad low on the north flank of the Alaska Range east of the Wood River (T. 10 S., R. 1 E.) indicates another basin under the Tanana lowland that extends eastward off the map area towards Delta Junction, where its presence was confirmed by both gravity and seismic data. Gravity modelling suggests that the base of the Usibelli Group in the area north of Nenana (T. 2 S., R. 8 W.) is about 3,000 to 3,350 m beneath the ground surface. Organic geochemical studies indicate that mudstones and coals in the Usibelli Group are potential sources of petroleum; calculations based on borehole temperatures suggest that, in the area of the gravity low, these rocks may have been buried deeply enough to generate oil and gas. Two exploratory wells, the Union Nenana No. 1 and the ARCO Totek Hills No. 11, were drilled some distance away from the gravity low in areas where the Usibelli Group is thin. Mudlogs show that both wells were dry holes that bottomed in schist and had gas shows associated with coal beds in the Usibelli Group, but no reported signs of oil.

Alaska↗
USGS1998

Geologic map of the Dao, Harmakhis, and Reull Valles region of Mars

The geology for this map was compiled using Viking Orbiter images on 1:500,000- scale photomosaics of the Mars Transverse Mercator quadrangles -40262, -40267, and -40272. This map represents a detailed extension of regional geologic mapping of the east Hellas rim (Crown and others 1990, 1992) and is published at 1:1,000,000 scale. The map area is on the east rim of one of the largest impact structures in the Solar System, the ~2,000-km-diameter Hellas basin (fig. 1). Channeled plains, with Dao, Harmakhis , and Reull Valles as the primary drainage features, dominate much of the surface within the map area. Dao Vallis is the downstream extension of Niger Vallis , which originates on the south flank of Hadriaca Patera, north of the map area. Harmakhis Vallis and Reull Vallis appear to intersect near latitutude 38°30' S., longitude 264°30'; Harmakhis Vallis trends southwest and Reull Vallis trends southeast from the area of intersection. The source area for these major outflow channels is at the intersection of two principal rings of multiring impact basins (Potter, 1976; Schultz and Frey, 1990; fig. 1). Hellas basin is centered southwest of the map area, and the proposed Hesperia basin is centered northeast of the map area (Schultz and Frey, 1990). The eastern part of the map area contains extensive remnants of ancient mountains and crater rim materials, along with large mesa-like features. Landforms over the entire map area appear to have been modified by multiple erosional events including downslope movement, eolian, and fluvial processes. The purpose of mapping the geology of the Dao, Harmakhis , and Reull Valles region of Mars is to refine stratigraphic and geomorphologic relations among the geologic units in thearea in order to better understand the nature of, relative timing of, and interactions among martian highland surface processes.

IMAP↗
USGS1998

Geologic map of the MTM -85280 quadrangle, Planum Australe region of Mars

The polar deposits on Mars are of great interest because they probably record martian climate variations (Thomas and others, 1992). The area shown on this map includes polar layered deposits with distinct low-albedo features and a sharp boundary between the layered deposits and the moderately cratered unit that forms the floor of Chasma Australe. Detailed mapping of this quadrangle was undertaken to further investigate the geologic relations between the albedo features and the layered deposits and to better constrain the recent geologic history of the south polar region. Dark dunes in the north polar region appear to be derived from erosion of the layered deposits, but the source of dark material in the south polar region is less clear (Thomas and Weitz, 1989). The presence of dark material in the brighter, redder layered deposits is paradoxical (Herkenhoff and Murray, 1990a); resolving this paradox is likely to result in a better understanding of the origin and evolution of the layered deposits and, therefore, the mechanisms by which global climate variations are recorded. Published geologic maps of the south polar region of Mars have been based on images acquired by either Mariner 9 (Condit and Soderblom, 1978; Scott and Carr, 1978) or the Viking Orbiters (Tanaka and Scott, 1987). The extent of the layered deposits mapped previously from Mariner 9 data is different from that mapped using Viking Orbiter images, and the present map agrees with the map by Tanaka and Scott (1987): the floor of Chasma Australe is not mapped as layered deposits. The residual polar ice cap, areas of partial frost cover, the layered deposits, and two nonvolatile surface units - the dust mantle and the dark material - were mapped by Herkenhoff and Murray (1990a) at 1:2,000,000 scale using a color mosaic of Viking Orbiter images. This mosaic and an additional Viking color mosaic were used to confirm the identification of the nonvolatile Amazonian units for this map and to test hypotheses for their origin and evolution. The colors and albedos of these units, as measured in places outside this map area, are presented in table 1 and figure 1. Accurately measuring the color and albedo of the units in this map area was not possible due to low signal/noise in the part of the red/violet mosaic (corrected for atmospheric scattering) that includes this area (Herkenhoff and Murray, 1990a). However, color/albedo unit boundaries in this area are visible in color mosaics that have not been corrected for atmospheric scattering effects. Therefore, while the color and albedo of various units on this map cannot be precisely quantified and compared with the values in table 1 and figure 1, color/albedo units can still be recognized. Because the resolution of the color mosaics is not sufficient to map these units in detail at 1:500,000 scale, contacts between them were recognized and mapped using higher resolution black-and-white Viking and Mariner 9 images. Only two possible impact craters in the layered deposits have been found in the area mapped; both are slightly elongate rather than circular. One, 1.6 km in diameter at lat 86.6° S., long 268°, was recognized by Plaut and others (1988); the other, about 3 km in diameter, is at lat 82.8° S., long 277°. Although the crater statistics are poor (only 16 likely impact craters found in the entire south polar layered deposits), these observations generally support the conclusions that the south polar layered deposits are Late Amazonian in age and that some areas have been exposed for at least 120 million years (Plaut and others, 1988; Herkenhoff and Murray, 1992, 1994). However, the recent cratering flux on Mars is poorly constrained, so inferred ages of surface units are uncertain. The Viking Orbiter 2 images used to construct the base were taken during the southern summer of 1977, with resolutions no better than 180 m/pixel. (The "less than 100 m per picture element" in Notes on Base of the controlled photomosaic base [U.S. Geological Survey, 1986] is incorrect.) A digital mosaic of Mariner 9 images was also constructed to aid in mapping. The Mariner 9 images were taken during the southern summer of 1971-72 and have resolutions as high as 90 m/pixel. However, usefulness of the Mariner 9 mosaic is limited by incomplete coverage and atmospheric dust opacity.

IMAP↗
USGS1998

Bedrock geologic map of the Yucca Mountain area, Nye County, Nevada

Yucca Mountain, Nye County, Nevada, has been identified as a potential site for underground storage of high-level radioactive nuclear waste. Detailed bedrock geologic maps form an integral part of the site characterization program by providing the fundamental framework for research into the geologic hazards and hydrologic behavior of the mountain. This bedrock geologic map provides the geologic framework and structural setting for the area in and adjacent to the site of the potential repository. The study area comprises the northern and central parts of Yucca Mountain, located on the southern flank of the Timber Mountain-Oasis Valley caldera complex, which was the source for many of the volcanic units in the area. The Timber Mountain-Oasis Valley caldera complex is part of the Miocene southwestern Nevada volcanic field, which is within the Walker Lane belt. This tectonic belt is a northwest-striking megastructure lying between the more active Inyo-Mono and Basin-and-Range subsections of the southwestern Great Basin. Excluding Quaternary surficial deposits, the map area is underlain by Miocene volcanic rocks, principally ash-flow tuffs with lesser amounts of lava flows. These volcanic units include the Crater Flat Group, the Calico Hills Formation, the Paintbrush Group, and the Timber Mountain Group, as well as minor basaltic dikes. The tuffs and lava flows are predominantly rhyolite with lesser amounts of latite and range in age from 13.4 to 11.6 Ma. The 10-Ma basaltic dikes intruded along a few fault traces in the north-central part of the study area. Fault types in the area can be classified as block bounding, relay structures, strike slip, and intrablock. The block-bounding faults separate the 1- to 4-km-wide, east-dipping structural blocks and exhibit hundreds of meters of displacement. The relay structures are northwest-striking normal fault zones that kinematically link the block-bounding faults. The strike-slip faults are steep, northwest-striking dextral faults located in the northern part of Yucca Mountain. The intrablock faults are modest faults of limited offset (tens of meters) and trace length (less than 7 km) that accommodated intrablock deformation. The concept of structural domains provides a useful tool in delineating and describing variations in structural style. Domains are defined across the study area on the basis of the relative amount of internal faulting, style of deformation, and stratal dips. In general, there is a systematic north to south increase in extensional deformation as recorded in the amount of offset along the block-bounding faults as well as an increase in the intrablock faulting. The rocks in the map area had a protracted history of Tertiary extension. Rocks of the Paintbrush Group cover much of the area and obscure evidence for older tectonism. An earlier history of Tertiary extension can be inferred, however, because the Timber Mountain-Oasis Valley caldera complex lies within and cuts an older north-trending rift (the Kawich-Greenwater rift}. Evidence for deformation during eruption of the Paintbrush Group is locally present as growth structures. Post-Paintbrush Group, pre-Timber Mountain Group extension occurred along the block-bounding faults. The basal contact of the 11.6-Ma Rainier Mesa Tuff of the Timber Mountain Group provides a key time horizon throughout the area. Other workers have shown that west of the study area in northern Crater Flat the basal angular unconformity is as much as 20° between the Rainier Mesa and underlying Paintbrush Group rocks. In the westernmost part of the study area the unconformity is smaller (less than 10°), whereas in the central and eastern parts of the map area the contact is essentially conformable. In the central part of the map the Rainier Mesa Tuff laps over fault splays within the Solitario Canyon fault zone. However, displacement did occur on the block-bounding faults after deposition of the Rainier Mesa Tuff inasmuch as it is locally caught up in the hanging-wall deformation of the block-bounding faults. Therefore, the regional Tertiary to Recent extension was protracted, occurring prior to and after the eruption of the tuffs exposed at Yucca Mountain.

Nevada↗
USGS2000

Digital data and geologic map of the Powder Mill Ferry Quadrangle, Shannon and Reynolds counties, Missouri

The geology of the Powder Mill Ferry 7 1/2-minute quadrangle , Shannon and Reynolds Counties, Missouri was mapped from 1997 through 1998 as part of the Midcontinent Karst Systems and Geologic Mapping Project, Eastern Earth Surface Processes Team. The map supports the production of a geologic framework that will be used in hydrogeologic investigations related to potential lead and zinc mining in the Mark Twain National Forest adjacent to the Ozark National Scenic Riverways (National Park Service). Digital geologic coverages will be used by other federal and state agencies in hydrogeologic analyses of the Ozark karst system and in ecological models.

IMAP↗
USGS2001

Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado

New 1:24,000-scale geologic mapping in the Colorado National Monument Quadrangle and adjacent areas, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of and data for the stratigraphy, structure, geologic hazards in the area from the Colorado River in Grand Valley onto the Uncompahgre Plateau. The plateau drops abruptly along northwest-trending structures toward the northeast 800 m to the Redlands area and the Colorado River in Grand Valley. In addition to common alluvial and colluvial deposits, surficial deposits include Holocene and late Pleistocene charcoal-bearing valley-fill deposits, late to middle Pleistocene river-gravel terrace deposits, Holocene to middle Pleistocene younger, intermediate, and old fan-alluvium deposits, late to middle Pleistocene local gravel deposits, Holocene to late Pleistocene rock-fall deposits, Holocene to middle Pleistocene young and old landslide deposits, Holocene to late Pleistocene sheetwash deposits and eolian deposits, and Holocene Cienga-type deposits. Only the lowest part of the Upper Cretaceous Mancos Shale is exposed in the map area near the Colorado River. The Upper and Lower? Cretaceous Dakota Formation and the Lower Cretaceous Burro Canyon Formation form resistant dipslopes in the Grand Valley and a prominent ridge on the plateau. Less resistant strata of the Upper Jurassic Morrison Formation consisting of the Brushy Basin, Salt Wash, and Tidwell Members form slopes on the plateau and low areas below the mountain front of the plateau. The Middle Jurassic Wanakah Formation nomenclature replaces the previously used Summerville Formation. Because an upper part of the Middle Jurassic Entrada Formation is not obviously correlated with strata found elsewhere, it is therefore not formally named; however, the lower rounded cliff former Slickrock Member is clearly present. The Lower Jurassic silica-cemented Kayenta Formation forms the cap rock for the Lower Jurassic carbonate-cemented Wingate Sandstone, which forms the impressive cliffs of the monument. The Upper Triassic Chinle Formation was deposited on the eroded and weathered Middle Proterozoic meta-igneous gneiss, pegmatite dikes, and migmatitic gneiss. Structurally the area is deceptively challenging. Nearly flat-lying strata on the plateau are folded by northwest-trending fault-propagation folds into at least two S-shaped folds along the mountain front of the plateau. Strata under Grand Valley dip at about 6 degrees to the northeast. In the absence of local evidence, the uplifted plateau is attributed to Laramide deformation by dated analogous structures elsewhere in the Colorado Plateau. The major exposed fault records high-angle reverse relationships in the basement rocks but dissipates strain as a triangular zone of distributed microfractures and cataclastic flow into overlying Mesozoic strata that absorb the fault strain, leaving only folds. Evidence for younger, probably late Pliocene or early Pleistocene, uplift does exist at the antecedent Unaweep Canyon south and east of the map area. To what degree this younger deformation affected the map area is unknown. Several geologic hazards affect the area. Middle and late Pleistocene landslides involving the smectite-bearing Brushy Basin Member of the Morrison Formation are extensive on the plateau and common in the Redlands below the plateau. Expansive clay in the Brushy Basin and other strata create foundation stability problems for roads and homes. Flash floods create a serious hazard to people on foot in narrow canyons in the monument and to homes close to water courses downstream from narrow restrictions close to the monument boundary.

Colorado↗
USGS2003

Geologic map of MTM -45252 and-45257 quadrangles, Reull Vallis region of Mars

Mars Transverse Mercator (MTM) quadrangles -45252 and -45257 (latitude 42.5° S. to 47.5°S., longitude 250° W. to 260° W.) cover a portion of the highlands of Promethei Terra east of Hellas basin. The map area consists of heavily cratered ancient highland materials having moderate to high relief, isolated knobs and massifs of rugged mountainous material, and extensive tracts of smooth and channeled plains. Part of the ~1,500-km-long Reull Vallis outflow system is within the map area. The area also contains surficial deposits, such as the prominent large debris aprons that commonly surround highland massifs. Regional slopes are to the west, toward the Hellas basin, as indicated by topographic maps of Mars. Approximately 60 percent of the surface of Mars is covered by rugged, heavily cratered terrains believed to represent the effects of heavy bombardment in the inner solar system about 4.0 billion years ago. Much of this terrain, including that within the map area, records a long history of modification by tectonism, fluvial processes, mass wasting, and eolian activity. The presence of fluvial features to the east of Hellas basin, including Reull Vallis and other smaller channels, has significant implications for past environmental conditions. The degraded terrains surrounding Hellas basin provide constraints on the role and timing of volatile-driven activity in the evolution of the highlands. Current photogeologic mapping at 1:500,000 scale (see also Mest and Crown, 2002) from analysis of Viking Orbiter images complements previous geomorphic studies of Reull Vallis and other highland outflow systems, drainage networks, and highland debris aprons, as well as regional geologic mapping studies and geologic mapping of Hellas basin as a whole at 1:5,000,000 scale. Viking Orbiter image coverage of the map area generally ranges from 160 to 220 m/pixel; the central part of the map area is covered by higher resolution images of about 47 m/pixel. Crater size-frequency distributions have been compiled to constrain the relative ages of geologic units and determine the timing and duration of inferred geologic processes.

IMAP↗
USGS2003

Geologic map of the Salmon National Forest and vicinity, east-central Idaho

The geology of the Salmon National Forest, Idaho, was compiled from published and unpublished sources and new field mapping by Evans, Lund, Tysdal, and Winkler between 1997 and 2001. The geology was compiled onto 1:100,000-scale topographic base maps for input into a geographic information system (GIS). The digital geologic map database can be queried in many ways to produce a variety of geologic maps.

IMAP↗
USGS2002

Geologic Map of the Katmai Volcanic Cluster, Katmai National Park, Alaska

This digital publication contains all the geologic map information used to publish U.S. Geological Survey Geologic Investigations Map Series I-2778 (Hildreth and Fierstein, 2003). This is a geologic map of the Katmai volcanic cluster on the Alaska Peninsula (including Mount Katmai, Trident Volcano, Mount Mageik, Mount Martin, Mount Griggs, Snowy Mountain, Alagogshak volcano, and Novarupta volcano), and shows the distribution of ejecta from the great eruption of June, 1912 at Novarupta. Widely scattered erosional remnants of volcanic rocks, unrelated to but in the vicinity of the Katmai cluster, are also mapped. Distribution of glacial deposits, large landslides, debris avalanches, and surficial deposits are a snapshot of an ever-changing landscape.

IMAP↗
USGS2003

Geologic Map of the Wilderness and Handy Quadrangles, Oregon, Carter, and Ripley Counties, Missouri

The bedrock exposed in the Wilderness and Handy Quadrangles, Missouri, comprises Early Ordovician aged dolomite, sandstone, and chert. The sedimentary rocks are nearly flat-lying except where they are adjacent to faults. The carbonate rocks are karstified and the area contains numerous sinkholes, springs, caves, and losing-streams. This map is one of several being produced under the U.S. Geological Survey National Cooperative Geologic Mapping Program to provide geologic data applicable to land-use problems in the Ozarks of south-central Missouri. Ongoing and potential industrial and agricultural development in the Ozarks region has presented issues of ground-water quality in karst areas. These quadrangles contain significant areas of the Mark Twain National Forest, including part of the Eleven Point National Scenic Riverway and the Irish Wilderness Roadless Area. A National Park in this region (Ozark National Scenic Riverways, Missouri ) is concerned about the effects of activities in areas outside of their stewardship on the water resources that define the heart of this Park. This task applies geologic mapping and karst investigations to address issues surrounding competing land use in south-central Missouri. For more information see: http://geology.er.usgs.gov/eespteam/Karst/index.html

IMAP↗
USGS1965

Geology of the Elkmont quadrangle, Alabama-Tennessee

The Elkmont quadrangle is in parts of Limestone County, Ala., and Giles County, Tenn. The town of Elkmont, in the west-central part of the quadrangle, had a population of about 250 in 1960. Most of the fieldwork in the Elkmont quadrangle was done during an investigation of the ground-water resources of the Athens area, Alabama, of which the Elkmont quadrangle is a part. The investigation was made by the U.S. Geological Survey in cooperation with the Geological Survey of Alabama and the city of Athens. The northwestern one-third of the quadrangle is in the Nashville Basin section of the Interior Low Plateaus physiographic province. Here the topography is characterized by steep-sided hills, narrow stream valleys, relatively steep stream gradients, and narrow drainage divides. Drainage is generally northward into the Elk River, but Sulphur Creek, in the southwestern quarter of the quadrangle, flows westward into the Elk River. The Nashville Basin section is underlain by rocks of Ordovician age, but in places remnants of rocks of Mississippian age cap hilltops. Altitudes in the Nashville Basin of the quadrangle range from about 590 feet in the north-central part to about 850 feet in the northeastern part. The southeastern two-thirds of the quadrangle is in the Highland Rim section of the Interior Low Plateaus province. The boundary separating the Nashville Basin and the Highland Rim is a very irregular but distinct escarpment that coincides with the contact of Mississippian rocks with older rocks. The Highland Rim in the Elkmont quadrangle is characterized by broad stream valleys, low stream gradients, and broad, low drainage divides. Drainage is southward into the Tennessee River. The Highland Rim is capped by rocks of Mississippian age, but in the southeastern part of the quadrangle along Piney Creek, and in a large sinkhole in the northeastern part, rocks of Ordovician and Devonian age are exposed. Altitudes on the Highland Rim range from about 700 feet in the southwestern part of the quadrangle to about 940 feet in the northeastern part. The rocks exposed in the Elkmont quadrangle consist chiefly of limestone and siliceous dolomite and range in age from Middle Ordovician to Early Mississippian. The Ordovician formations are correlated with those which crop out extensively in central Tennessee, where they have been subdivided and mapped in detail by the Tennessee Division of Geology, and also are correlated with those which crop out in the Salem quadrangle adjacent to the west (McMaster, 1964). The type areas for the Ordovician and Devonian formations referred to in this report are in central Tennessee. The Elkmont quadrangle is on the southern flank of the Nashville dome. The strata dip generally southwestward, but the regional dip is modified considerably by the presence of minor anticlines and synclines. The author is indebted to Mr. Robert Barnes of the Tennessee Division of Geology, with whom he spent 2 days in the field reviewing the Ordovician stratigraphy in the Elkmont quadrangle.

Alabama, Tennessee↗
USGS1969

(RLC-14) Geologic map of the Alphonsus region of the moon

This 1:250,000- scale geologic map is one of a series prepared largely from photographs transmitted by Ranger IX (reproduced in a report by Jet Propulsion Lab., 1966). It depicts the geology of the crater Alphonsus (in which Ranger IX impacted) and environs. The primary objective of the mapping was to apply extant lunar mapping techniques used on relatively small scale telescopic photographs to the larger scale Ranger photographs, in preparation for extensive analysis of Lunar Orbiter photography in support of the Apollo program. An additional objective was to shed more light on the formation of Alphonsus and its associated features. The map outlines rock units that are inferred from surface features and characteristics, such as topography and albedo. Each rock unit is assigned an age and arranged in the explanation so that the youngest unit are at the top and the oldest at the bottom. The age classification is based on the early work of Shoemaker and Hackman (1962), and subsequent revisions reported by McCauley (1967) and Wilhelms (1966). Geology of the region has been mapped at a scale of 1:1,000,000 on the basis of Earth-based photographs and observations (Howard and Masursky , 1968). A more detailed, 1;50,000-scale map of part of the Alphonsus floor was prepared by McCauley (1969), who used Ranger IX photographs as his source of geologic information.

IMAP↗
USGS1974

Geologic map and sections of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado

This map was first published as a printed edition in 1974. The geologic data have now been captured digitally and are presented here along with images of the printed map sheets. The map encompasses the area of four 7.5-minute quadrangles between 39º15' and 39º 30'N and 106º15' and 106º30'W in the Sawatch and Gore mountain ranges, and upper part of the Arkansas River drainage in central Colorado. The Holy Cross geologic map depicts in detail the complex geology at the north end of the Sawatch Range on the west at its junction with south end of the Gore Range on the east. The ranges are separated in the southern part of the map area by the upper reaches of the Arkansas River, and in the northeast part by the narrow valley of the upper Eagle River. Sixty map units and numerous individual beds and thin units within the principal map units are shown. Paleoproterozoic and Mesoproterozoic metamorphic rocks are the principal rocks of the Sawatch Range. In the Gore Range, lower and upper Paleozoic sedimentary rocks rest unconformably on the Precambrian metamorphic rocks. Paleozoic rocks that range in age from Upper Cambrian though Middle Pennsylvanian support the Gore Range along the eastern quarter of the map. The sequence includes a basal quartzite overlain by interbedded, shale, dolomite, quartzite, and sandstone. The Leadville Dolomite, below the dark shale, is the host rock for the ore deposits at Leadville and the neighboring lead-zinc-silver districts. A wide range of Miocene to Cretaceous intrusive rocks dip east off the Sawatch Range. The Dry Union Formation of Pliocene and Miocene age fills the valley of the Arkansas River and is covered by Quaternary alluvium and glacial sediment. Glacial deposits of Bull Lake, Pinedale, and neoglacial age are present in many of the mountain valleys. The geologic structure of the quadrangle is complex in geometry and time with a distinct structural and geographic break along the west front of the Gore Range in the eastern quarter of the quadrangle. In general, Paleozoic strata intruded by Tertiary and Cretaceous irregular linear plutons and sills of the Gore Range are tilted east from the Sawatch Range. These rocks are broken by major normal faults in a complex pattern commonly associated with Paleocene? and Cretaceous intrusive porphyries. In the Sawatch Range, two large Precambrian igneous complexes are separated by a broad shear zone of Precambrian age that extends northwest across the quadrangle and beneath Paleozoic rocks of the Gore Range. Down-to-valley normal faults define the margins of the Arkansas and upper Eagle River valleys. The Leadville, Sugarloaf, and St. Kevin districts have produced significant amounts of silver. The Homestake mine at the head of West Tennessee Creek produced silver and lead from veins bearing siderite and barite. Scattered veins in shear zones along Homestake Creek are mainly argentiferous galena veins; some are quartz and copper. Veins at Holy Cross City produced gold. Other veins in the area have produced gold, silver, and minor amounts of copper.

Colorado↗
USGS1980

Maps showing geology and shallow structure of eastern Rhode Island Sound and Vineyard Sound, Massachusetts

This report presents results of marine studies conducted by the U.S. Geological Survey (USGS) during the summers of 1975 and 1976 in eastern Rhode Island Sound and Vineyard Sound (fig. 1) located off the southeastern coast of Massachusetts. The study was made in cooperation with the Massachusetts Department of Public Works and the New England Division of the U.S. Army Corps of Engineers. It covered an area of the Atlantic Inner Continental Shelf between latitude 41 deg 12' and 41 deg 33'N, and between longitude 70 deg 37' and 71 deg 15'W (see index map). Major objectives included assessment of sand and gravel resources, environmental impact evaluation both of offshore mining of these resources and of offshore disposal of solid waste and dredge spoil material, identification and mapping of the offshore geology, and determination of the geologic history of this part of the Inner Shelf. A total of 670 kilometers (km) of closely spaced high-resolution seismic-reflection profiles, 224 km of side-scan sonar data, and 16 cores totaling 90 meters (m) of recovered sediment, were collected during the investigation. This report is companion to geologic maps published for Cape Cod Bay (Oldale and O'Hara, 1975) and Buzzards Bay, Mass. (Robb and Oldale, 1977).

Massachusetts, Rhode Island↗
USGS1985

Reconnaissance geologic map of part of the San Isidro Quadrangle, Baja California Sur, Mexico

The reconnaissance geology of part of the San Isidro 1:250,000-scale quadrangle of Baja California Sur, Mexico, was mapped in 1982, 1983, and 1984 to determine the age and stratigraphic relations of Tertiary sedimentary and volcanic rocks that comprise the bulk of the Sierra de la Giganta (southern Peninsular Ranges) and Pacific coastal plain. Focus was placed on determining the distribution and age of plateau-capping basalts, and on mapping the eastern limits of Paleogene marine strata and the western limits of the nonmarine Comondu Formation. The area was also examined for outcrops of pre-Tertiary crystalline rocks, however, none were found. Mapping was done on aerial photographs and transferred, where possible, to 1:50,000-scale topographic base maps. Areas with roads were field checked; however, in the northeast part of the map area, lack of roads prevented field checks. Previous geologic surveys of parts of the map area were made by horseback in the early 1920's; reports were published by Darton (1921), Heim (1922), and Beal (1948). Subsurface data from petroleum exploration and a geologic map were incorporated in a regional study by Mina (1957). The first radiometric ages of rocks from the map area were published by Gastil and others (1979). Recently determined radiometric ages and chemical analysis of volcanic rocks were reported by Hausback (1984) and by Sawlan and Smith (1984). Our study incorporates geologic mapping with age control based on new radiometric ages as well as paleontology, Flows and tuffs were dated by the K-Ar method. Fossil ages are based on diatom and mollusk assemblages.

Baja California Sur↗