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Bruce Bryant

Publications and source records attributed to Bruce Bryant.

At least 19 recordsLinked to original sources
USGS2017

Geologic setting and stratigraphy of the Ziegler Reservoir fossil site, Snowmass Village, Colorado

The geologic setting of the Ziegler Reservoir fossil site is somewhat unusual – the sediments containing the Pleistocene fossils were deposited in a lake on top of a ridge. The lake basin was formed near the Town of Snowmass Village, Colorado when a glacier flowing down Snowmass Creek Valley became thick enough to overtop a low point in the eastern valley wall and entered the head of Brush Creek Valley. When the glacier retreated at the end of the marine isotope stage (MIS) 6, ~155-130 ka (thousands of years before present), the Brush Creek Valley lobe left behind a moraine that impounded a small alpine lake. The lake was initially ~10 m deep and was highly productive during most of its existence based on the abundant and exquisitely preserved organic material present in the sediments. Over time, the basin slowly filled with (mostly) eolian sediment such that by ~85 ka it contained more of a marsh or wetland than a true lake. Open water conditions returned briefly between ~75 and 55 ka before the impoundment was finally breached to the east, establishing ties with the Brush Creek drainage system and creating an alpine meadow that persisted until historic times.

Colorado↗
USGS2017

A high-elevation, multi-proxy biotic and environmental record of MIS 6-4 from the Ziegler Reservoir fossil site, Snowmass Village, Colorado, USA

In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean–atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010–2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA) revealed a nearly continuous, lacustrine/wetland sedimentary sequence that preserved evidence of past plant communities between ~ 140 and 55 ka, including all of MIS 5. At an elevation of 2705 m, the Ziegler Reservoir fossil site also contained thousands of well-preserved bones of late Pleistocene megafauna, including mastodons, mammoths, ground sloths, horses, camels, deer, bison, black bear, coyotes, and bighorn sheep. In addition, the site contained more than 26,000 bones from at least 30 species of small animals including salamanders, otters, muskrats, minks, rabbits, beavers, frogs, lizards, snakes, fish, and birds. The combination of macro- and micro-vertebrates, invertebrates, terrestrial and aquatic plant macrofossils, a detailed pollen record, and a robust, directly dated stratigraphic framework shows that high-elevation ecosystems in the Rocky Mountains of Colorado are climatically sensitive and varied dramatically throughout MIS 5.

Colorado↗
USGS2016

Mountains, glaciers, and mines—The geological story of the Blue River valley, Colorado, and its surrounding mountains

This report describes, in a nontechnical style, the geologic history and mining activity in the Blue River region of Colorado, which includes all of Summit County. The geologic story begins with the formation of ancient basement rocks, as old as about 1700 million years, and continues with the deposition of sedimentary rocks on a vast erosional surface beginning in the Cambrian Period (about 530 million years ago). This deposition was interrupted by uplift of the Ancestral Rocky Mountains during the late Paleozoic Era (about 300 million years ago). The present Rocky Mountains began to rise at the close of the Mesozoic Era (about 65 million years ago). A few tens of millions years ago, rifting began to form the Blue River valley; a major fault along the east side of the Gore Range dropped the east side down, forming the present valley. The valley once was filled by sediments and volcanic rocks that are now largely eroded. During the last few hundred-thousand years, at least two periods of glaciation sculpted the mountains bordering the valley and glaciers extended down the Blue River valley as far south as present Dillon Reservoir. Discovery of deposits of gold, silver, copper, and zinc in the late 1800s, particularly in the Breckenridge region, brought an influx of early settlers. The world-class molybdenum deposit at Climax, mined since the First World War, reopened in 2012 after a period of closure. The report includes a glossary to explain geologic terms used in the text, and numerous photos, maps, and diagrams illustrate the geologic principles discussed. References for further reading are also included.

Colorado↗
USGS2011

Geologic map of the Bailey 30' x 60' quadrangle, North-Central Colorado

The Bailey, Colo. 1:100,000-scale quadrangle lies within two physiographic and geologic provinces in central Colorado: 1) the Front Range and 2) South Park. Most of the Front Range is composed of Proterozoic rocks ranging in age from 1,790 Ma to 1,074 Ma. Along the eastern flanks and within the Denver Basin, sedimentary rocks ranging from Pennsylvanian to Cretaceous are deformed and steeply tilted to the east. Upper Cretaceous through Paleocene rocks were deposited in the foreland (that is, the Front Range eastern flank) and hinterland (that is, South Park) of this thrust and reverse fault system developed during the Late Cretaceous to Paleocene Laramide orogeny. Within South Park, rocks range in age from Pennsylvanian to Miocene with Quaternary deposits indicating tectonic subsidence of the basin. These rocks record five major geologic episodes: 1) the Paleozoic Anasazi uplift that formed the Ancestral Rockies, 2) the Late Cretaceous to Paleocene Laramide orogeny, 3) widespread Eocene to Oligocene volcanism, 4) Oligocene-Quaternary tectonics, and 5) Quaternary glacial episodes.

Colorado↗
USGS2011

Geologic map of the eastern half of the Vail 30' x 60' quadrangle, Eagle, Summit, and Grand Counties, Colorado

Recent mapping and geochronologic studies for the eastern half of the Vail 1:100,000-scale quadrangle have significantly improved our understanding of (1) Paleoproterozoic history of the basement rocks of the Gore Range and Williams Fork Mountains (western margin of the Front Range), (2) the Late Paleozoic history of the Gore fault system, (3) Laramide contractional tectonism, including deformation along the Gore fault and Williams Range thrust, (4) Oligocene and younger extensional history of the Blue River half graben (The northern extent of the Rio Grande rift), and (5) late Neogene and Quaternary surficial history. The recently active Gilman mining district, a major producer of zinc and lead, is in the southwestern corner of the map area. Marine sediments and mafic to felsic volcanic rocks deposited between about 1,740 and 1,780 m.y. were generally metamorphosed to amphibolite grade and intruded and deformed by mostly calc-alkalic granitic rocks during an orogenic episode that lasted about 110 m.y. The distribution of well-studied Upper Cambrian to thick Upper Cretaceous platform sediments is now greatly improved, which allows a better definition of the late Paleozoic uplift, erosion, and flanking sedimentation of the ancestral Front Range. Detailed mapping has also better defined the geometry of Late Cretaceous to early Tertiary Laramide deformation along both the Gore fault system and Williams Range thrust, as well as increased understanding of the details of mostly Neogene extension along the Blue River normal fault system (the western margin of the Blue River half graben). Scarps along the latter fault system indicate movement may be as young as Holocene. Detailed mapping of surficial deposits has defined and described (1) six ages of terrace alluvium, (2) three general ages of landslides, (3) glacial and periglacial deposits, and (4) fan, pediment, talus, and debris-flow deposits. The map is intended as a database for a variety of land-use and scientific purposes, including (1) assessment of geologically stable building sites, (2) planning for road and highway construction, (3) assessment of groundwater resources, (4) assessment of mineral resources, (5) determining geologic-hazard potential (flooding, landslide, rockfall, and seismic risk), (6) evaluating the structure of the northern Rio Grande rift in the Blue River valley, (7) improvement in understanding of the sedimentary section, which spans the period from the Cambrian to the Holocene, and (8) new insights into the geologic history of the Proterozoic basement rocks, including a number of new radiometric dates.

Scientific Investigations Map↗
USGS2010

Geologic map of the Fraser 7.5-minute quadrangle, Grand County, Colorado

The geologic map of the Fraser quadrangle, Grand County, Colo., portrays the geology along the western boundary of the Front Range and the eastern part of the Fraser basin near the towns of Fraser and Winter Park. The oldest rocks in the quadrangle include gneiss, schist, and plutonic rocks of Paleoproterozoic age that are intruded by younger plutonic rocks of Mesoproterozoic age. These basement rocks are exposed along the southern, eastern, and northern margins of the quadrangle. Fluvial claystone, mudstone, and sandstone of the Upper Jurassic Morrison Formation, and fluvial sandstone and conglomeratic sandstone of the Lower Cretaceous Dakota Group, overlie Proterozoic rocks in a small area near the southwest corner of the quadrangle. Oligocene rhyolite tuff is preserved in deep paleovalleys cut into Proterozoic rocks near the southeast corner of the quadrangle. Generally, weakly consolidated siltstone and minor unconsolidated sediments of the upper Oligocene to upper Miocene Troublesome Formation are preserved in the post-Laramide Fraser basin. Massive bedding and abundant silt suggest that loess or loess-rich alluvium is a major component of the siltstone in the Troublesome Formation. A small unnamed fault about one kilometer northeast of the town of Winter Park has the youngest known displacement in the quadrangle, displacing beds of the Troublesome Formation. Surficial deposits of Pleistocene and Holocene age are widespread in the Fraser quadrangle, particularly in major valleys and on slopes underlain by the Troublesome Formation. Deposits include glacial outwash and alluvium of non-glacial origin; mass-movement deposits transported by creep, debris flow, landsliding, and rockfall; pediment deposits; tills deposited during the Pinedale and Bull Lake glaciations; and sparse diamictons that may be pre-Bull Lake till or debris-flow deposits. Some of the oldest surficial deposits may be as old as Pliocene.

Scientific Investigations Map↗
USGS2009

Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides

The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

Alabama, Georgia, Kentucky, Maryland, North Caroli↗
USGS2008

Geology of the Northern Part of the Harcuvar Complex, West-Central Arizona

In west-central Arizona near the northeast margin of the Basin and Range Province, the Rawhide detachment fault separates Tertiary and older rocks lacking significant effects of Tertiary metamorphism from Precambrian, Paleozoic, and Mesozoic rocks in the Harcuvar metamorphic core complex below. Much of the northern part of the Harcuvar complex in the Buckskin and eastern Harcuvar Mountains is layered granitic gneiss, biotite gneiss, amphibolite, and minor pelitic schist that was probably deformed and metamorphosed in Early Proterozoic time. In the eastern Buckskin Mountains, Early and Middle Proterozoic plutons having U-Pb zircon ages of 1,683?6.4 mega-annum (Ma) and 1,388?2.3 Ma, respectively, intruded the layered gneiss. Small plutons of alkaline gabbro and diorite intruded in Late Jurassic time. A sample of mylonitized diorite from this unit has a U-Pb zircon age of 149?2.8 Ma. In the Early Cretaceous, amphibolite facies regional metamorphism was accompanied by partial melting and formation of migmatite. Zircon from a granitic layer in migmatitic gneiss in the eastern Harcuvar Mountains has a U-Pb age of 110?3.7 Ma. In the Late Cretaceous, sills and plutons of the granite of Tank Pass were emplaced in both the Buckskin and eastern Harcuvar Mountains. In the Buckskin Mountains those intrusions are locally numerous enough to form an injection migmatite. A pluton of this granite crops out over almost half the area of the eastern Harcuvar Mountains. Paleozoic and Mesozoic sedimentary rocks were caught as slices along south-vergent Cretaceous thrusts related to the Maria fold and thrust belt and were metamorphosed beneath a thick sheet of Proterozoic crustal rocks. Inception of volcanism and basin formation in upper-plate rocks indicates that regional extension started at about 26 Ma, in late Oligocene. The Swansea Plutonic Suite, composed of rocks ranging from gabbro to granite, intruded the lower-plate rocks in the Miocene and Oligocene(?). Granite and a gabbro from the suite have a U-Pb zircon age of 21.86?0.60 Ma. Previously published 40Ar/39Ar ages of hornblende suggest that some of the Swansea Suite is Oligocene. The felsic rocks contain numerous inclusions ranging from porphyritic granite to porphyritic granodiorite. A sample from one inclusion has a U-Pb zircon age of 1,409?6.3 Ma. A discordia line for the U-Pb zircon data from the Swansea Plutonic Suite has an upper intercept at 1,408?3.4 Ma. The Swansea Plutonic Suite probably formed by interaction between mantle material and plutonic rocks at least as old as Middle Proterozoic. An irregular layer in the middle crust, which is thickest under and adjacent to the Buckskin Mountains, may be the level where that interaction took place. During extensional deformation these rocks and all the older rocks were displaced southwest from beneath the rocks of the Colorado Plateau transition zone below an area extending 50?80 kilometers northeast of the Buckskin Mountains as far as Bagdad, Arizona, or beyond. At that time the rocks were variably mylonitized, and a northeast-trending lineation formed. Much of the evidence for the complex sequence of structural events preserved in these rocks in the western Harcuvar Mountains has been obliterated in the northern Harcuvar complex by Miocene deformation.

Professional Paper↗
USGS2008

Geologic map of the Denver West 30' x 60' quadrangle, north-central Colorado

The Denver West quadrangle extends east-west across the entire axis of the Front Range, one of numerous uplifts in the Rocky Mountain region in which Precambrian rocks are exposed. The history of the basement rocks in the Denver West quadrangle is as old as 1,790 Ma. Along the east side of the range, a sequence of sedimentary rocks as old as Pennsylvanian, but dominated by Cretaceous-age rocks, overlies these ancient basement rocks and was upturned and locally faulted during Laramide (Late Cretaceous to early Tertiary) uplift of the range. The increasingly coarser grained sediments up section in rocks of latest Cretaceous to early Tertiary age record in remarkable detail this Laramide period of mountain building. On the west side of the range, a major Laramide fault (Williams Range thrust) places Precambrian rocks over Cretaceous sedimentary rocks. The geologic history of the quadrangle, therefore, can be divided into four major periods: (1) Proterozoic history, (2) Pennsylvanian to pre-Laramide, Late Cretaceous history, (3) Late Cretaceous to early Tertiary Laramide mountain building, and (4) post-Laramide history. In particular, the Quaternary history of the Denver West quadrangle is described in detail, based largely on extensive new mapping.

Scientific Investigations Map↗
USGS2006

Isotopic ages of rocks in the northern Front Range, Colorado

These maps, and the tables that accompany them, are a compilation of isotopic age determinations of rocks and minerals in four 1:100,000 quadrangles in the northern and central Front Range, Colorado. Phanerozoic (primarily Tertiary and Cretaceous) age data are shown on one map; Proterozoic data are on the other. A sample location map is included for ease of matching specific localities and data in the tables to the maps. Several records in the tables were not included in the maps because either there were ambiguous dates or lack of location precluded accurate plotting.

Open-File Report↗
USGS2004

The Colorado front range: anatomy of a Laramide uplift

Along a transect across the Front Range from Denver to the Blue River valley near Dillon, the trip explores the geologic framework and Laramide (Late Cretaceous to early Eocene) uplift history of this basement-cored mountain range. Specific items for discussion at various stops are (1) the sedimentary and structural record along the upturned eastern margin of the range, which contains several discontinuous, east-directed reverse faults; (2) the western structural margin of the range, which contains a minimum of 9 km of thrust overhang and is significantly different in structural style from the eastern margin; (3) mid- to late-Tertiary modifications to the western margin of the range from extensional faulting along the northern Rio Grande rift trend; (4) the thermal and uplift history of the range as revealed by apatite fission track analysis; (5) the Proterozoic basement of the range, including the significance of northeast-trending shear zones; and (6) the geologic setting of the Colorado mineral belt, formed during Laramide and mid-Tertiary igneous activity.

Colorado↗
USGS2003

Geologic map of the Vail East quadrangle, Eagle County, Colorado

New 1:24,000-scale geologic mapping along the Interstate-70 urban corridor in western Colorado, in support of the State/USGS Cooperative Geologic Mapping Project, is contributing to a more complete understanding of the stratigraphy, structure, tectonic evolution, and hazard potential of this rapidly developing region. The 1:24,000-scale Vail East quadrangle straddles the Gore fault system, the western structural boundary of the Gore Range. The Gore fault system is a contractional structure that has been recurrently active since at least the early Paleozoic and marks the approximate eastern boundary of the Central Colorado trough, a thick late Paleozoic depocenter into which thousands of meters of clastic sediment were deposited from several uplifts, including the ancestral Front Range. The Gore fault was active during both the late Paleozoic and Upper Cretaceous-lower Tertiary (Laramide) deformations. In addition, numerous north-northwest faults that cut the crystalline rocks of the Gore Range were active during at least 5 periods, the last of which was related to Neogene uplift of the Gore Range and formation of the northern Rio Grande rift. Early Proterozoic crystalline rocks underlie the high Gore Range, north and east of the Gore fault system. These rocks consist predominantly of migmatitic biotite gneiss intruded by mostly granitic rocks of the 1.667-1.750 Ma Cross Creek batholith, part of the 1,667-1,750 Ma Routt Plutonic Suite (Tweto, 1987). Southwest of the Gore fault, a mostly gently south-dipping sequence of Pennsylvanian Mimturn Formation, as thick as 1,900 m, and the Permian and Pennsylvanian Maroon Formation (only the basal several hundred meters are exposed in the quadrangle)were shed from the ancestral Front Range and overlie a thin sequence of Devonian and Cambrian rocks. The Minturn Formation is a sequence of interlayered pink, maroon, and gray conglomerate, sandstone, shale, and marine limestone. The Maroon Formation is mostly reddish conglomerate and sandstone. Glacial till of both the middle Pleistocene Bull Lake and late Pleistocene Pinedale glaciations are well exposed along parts of the Gore Creek valley and its tributaries, although human development has profoundly altered the outcrop patterns along the Gore Creek valley bottom. Landslides, some of which are currently active, are also mapped.

Miscellaneous Field Studies Map↗
USGS2002

Late Cenozoic deformation by evaporite tectonism in the Grand Hogback monocline, southwest of the White River uplift, Colorado

Along 50 km of the complex, southwest-dipping, Laramide Grand Hogback monocline, which wraps around the southwest flank of the White River uplift in westcentral Colorado, detailed mapping provides evidence of late Cenozoic collapse that resulted from subsurface flow, diapirism, and dissolution of Pennsylvanian Eagle Valley Evaporite. Numerous discontinuous, small-amplitude, strike-parallel folds and steeply dipping faults that overlie the evaporite are interpreted as the result of both flow-induced and dissolution-induced collapse and diapirism concentrated along cross-strike, radial valleys draining the uplift. Folding of an immature Pliocene conglomerate into a tight syncline by collapse into an underlying diapir emphasizes the young age of evaporite tectonism. Major evaporite diapirs in valleys penetrate overlying Pennsylvanian Eagle Valley and Pennsylvanian-Permian Maroon Formations. In the absence of a Miocene basaltic datum used to quantify collapse elsewhere in west-central Colorado, we quantify removal of evaporite by contrasting estimated original evaporite thicknesses with thicknesses of remaining evaporite based on surface structural control and cross section construction. We estimate that ∼40 km3 of evaporite were removed along the southwest flank, the majority of which came from cross-strike valleys and a minority from intervening drainage divides. The mechanism for initiation of flow of evaporite is interpreted to be late Cenozoic regional uplift and accompanying deep incision of valleys draining the White River uplift. Unloading of evaporite beneath these valleys channeled evaporite to flow northward up dip to diapirically extrude from overlying Maroon and Eagle Valley Formations. Laramide monoclinal structures change gradually along strike from a single monocline, which produced a complexly folded back thrust, to double monoclines stacked on one another, which are located close to bends in the flank of the uplift.

Colorado↗
USGS2002

40Ar/39Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River

40 Ar/ 39 Ar dating results of 133 samples from 84 late Cenozoic volcanic rocks provide emplacement ages that constrain the timing of evaporite collapse and the incision rates of the Colorado River. Our samples are from areas in west-central Colorado, both within and outside of the Carbondale and Eagle collapse centers. Significant pulses of volcanic activity occurred in the intervals from 24 to 22, 16 to 13, 11 to 9, and 8 to 7 Ma. In addition, small flows, widely spaced in time and space were emplaced during the last 4 m.y. Although individual basaltic flows appear to be chemically and isotopically homogeneous, there are significant geochemical and isotopic differences between flows, even between some flows that apparently have the same age within the limits of analytical precision. A low-relief early to middle Miocene erosional surface has been postulated in west-central Colorado. Our studies are consistent with the existence of a low-relief paleotopographic surface that is now at a minimum elevation range of ~2.9–3.4 km outside areas of collapse. Elevation departures from this range suggest that 1000 m of subsidence due to evaporite removal has locally occurred in the Carbondale and Eagle collapse centers. 40 Ar/ 39 Ar ages from downdropped and disrupted basaltic flows in the Carbondale center constrain initial collapse to >13 Ma, the timing of much of the evaporite-related collapse to the past 10–8 m.y., and an increase in the rate of collapse during the last 3 m.y. Ages and elevations of basaltic rocks above the Colorado River in Glenwood Canyon are used to calculate average apparent incision rates for the Colorado River in Glenwood Canyon of 24 mm/k.y. from 7.8 to 3.0 Ma. The average apparent incision rate increased by an order of magnitude to 242 mm/k.y. during the last 3 m.y

Colorado↗
USGS2002

Tertiary cooling and tectonic history of the White River uplift, Gore Range, and western Front Range, central Colorado: Evidence from fission-track and 39Ar/ 40Ar ages

Apatite fission-track (AFT) data from Proterozoic and Paleozoic rocks in the mountains of north central Colorado (White River Uplift, Gore Range, and western Front Range) record significant cooling that began with uplift and erosion related to the Laramide Orogeny and continued through the Tertiary to Pliocene time. The mountains immediately flanking the Blue River half graben (Williams Fork Mountains to the east and the Gore Range to the west) cooled significantly during the Neogene. The AFT ages along the flanks of the Blue River half graben are significantly younger than AFT ages farther to the east in the central and eastern Front Range and to the west in the White River uplift. In both of these areas, the apatite ages suggest Laramide cooling. The Williams Fork Mountains–Gore Range zone of young AFT ages extends southward adjacent to the axis of the Rio Grande rift through southern Colorado and New Mexico. These young ages result from a combination of elevated heat flow, uplift, and erosion along the axis of the Rio Grande rift during Neogene time. Zircons from Proterozoic rocks yield Proterozoic fission-track ages, indicating that this part of the Colorado basement has not been heated to temperatures 200 C since Middle Proterozoic time. A sanidine 40 Ar/ 39 Ar age of 27 Ma from a rhyolite tuff just above a basal boulder conglomerate of the Troublesome Formation in a tilted fault block within the Blue River half graben shows that Tertiary deposition started there in middle Oligocene time. Xenocrystic sanidine from a basalt stratigraphically higher than the rhyolite tuff has an age of 24 Ma. Thus, the basalt is significantly younger than its postulated source, the 32 Ma laccolithic complex at Green Mountain.

Colorado↗
USGS2002

Geologic map of the Storm King Mountain quadrangle, Garfield County, Colorado

New 1:24,000-scale geologic mapping in the Storm King Mountain 7.5' quadrangle, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new data on the structure on the south margin of the White River uplift and the Grand Hogback and on the nature, history, and distribution of surficial geologic units. Rocks ranging from Holocene to Proterozoic in age are shown on the map. The Canyon Creek Conglomerate, a unit presently known to only occur in this quadrangle, is interpreted to have been deposited in a very steep sided local basin formed by dissolution of Pennsylvanian evaporite late in Tertiary time. At the top of the Late Cretaceous Williams Fork Formation is a unit of sandstone, siltstone, and claystone from which Late Cretaceous palynomorphs were obtained in one locality. This interval has been mapped previously as Ohio Creek Conglomerate, but it does not fit the current interpretation of the origin of the Ohio Creek. Rocks previously mapped as Frontier Sandstone and Mowry Shale are here mapped as the lower member of the Mancos Shale and contain beds equivalent to the Juana Lopez Member of the Mancos Shale in northwestern New Mexico. The Pennsylvanian Eagle Valley Formation in this quadrangle grades into Eagle Valley Evaporite as mapped by Kirkham and others (1997) in the Glenwood Springs area. The Storm King Mountain quadrangle spans the south margin of the White River uplift and crosses the Grand Hogback monocline into the Piceance basin. Nearly flat lying Mississippian through Cambrian sedimentary rocks capping the White River uplift are bent into gentle south dips and broken by faults at the edge of the uplift. South of these faults the beds dip moderately to steeply to the south and are locally overturned. These dips are interrupted by a structural terrace on which are superposed numerous gentle minor folds and faults. This terrace has an east-west extent similar to that of the Canyon Creek Conglomerate to the north. We interpret that the terrace formed by movement of Eagle Evaporite from below in response to dissolution and diapirism in the area underlain by the conglomerate. A low-angle normal fault dipping gently north near the north margin of the quadrangle may have formed also in response to diapirism and dissolution in the area of the Canyon Creek Conglomerate. Along the east edge of the quadrangle Miocene basalt flows are offset by faults along bedding planes in underlying south-dipping Cretaceous rocks, probably because of diapiric movement of evaporite into the Cattle Creek anticline (Kirkham and Widmann, 1997). Steep topography and weak rocks combine to produce a variety of geologic hazards in the quadrangle.

Miscellaneous Field Studies Map↗
USGS2001

Geology, geochronology, geochemistry, and Pb-isotopic compositions of Proterozoic rocks, Poachie region, west-central Arizona — A study of the east boundary of the Proterozoic Mojave crustal province

The Poachie region at the south edge of the Colorado Plateau transition zone in western Arizona is underlain by early and middle Proterozoic plutonic rocks locally separated by screens of amphibolite-facies early Proterozoic metamorphic rocks and is in the eastern part of the Mojave crustal province, as shown by 35 Pb-isotope analyses of rocks and feldspars. Previously published mapping, 10 U-Pb zircon ages, 55 rock analyses, and other studies in the larger region of the transition zone lead to interpretation of the history and origin of the Proterozoic crust.

Arizona↗