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At least 91 records · Page 5Linked to original sources
USGS2009

The 16th International Geological Congress, Washington, 1933

In 1933, the International Geological Congress (IGC) returned to the United States of America (USA) for its sixteenth meeting, forty-two years after the 5 th IGC convened in Washington. The Geological Society of America and the U.S. Geological Survey (USGS) supplied the major part of the required extra-registration funding after the effects of the Great Depression influenced the 72 th U.S. Congress not to do so. A reported 1, 182 persons or organizations, representing fifty-four countries, registered for the 16 th IGC and thirty-four countries sent 141 official delegates. Of the total number of registrants, 665 actually attended the meeting; 500 came from the USA; and fifteen had participated in the 5 th IGC. The 16 th Meeting convened in the U.S. Chamber of Commerce Building from 22 to 29 July. The eighteen half-day scientific sections-orogenesis (four), major divisions of the Paleozoic (three), miscellaneous (three), batholiths and related intrusives (two), arid-region geomorphic processes and products (one), fossil man and contemporary faunas (one), geology of copper and other ore deposits (one), geology of petroleum (one), measuring geologic time (one), and zonal relations of metalliferous deposits (one)-included 166 papers, of which fifty (including several of the key contributions) appeared only by title. The Geological Society of Washington, the National Academy of Sciences, and the U.S. Bureau of Mines hosted or contributed to evening presentations or receptions. Twenty-eight of the 16 th IGC's thirty new guidebooks and one new USGS Bulletin aided eight pre-meeting, seven during-meeting, and four post-meeting field trips of local, regional, or national scope. The remaining two new guidebooks outlined the USA's structural geology and its stratigraphic nomenclature. The 16 th IGC published a two-volume monograph on the world's copper resources (1935) and a two-volume report of its proceedings (1936).

Episodes↗
USGS2013

Field guide to the geology of the Denali National Park Road and the Parks Highway from Cantwell to Healy

The Denali National Park & Preserve area provides one of the few opportunities in Alaska for road-side access to good rock outcrops. The rocks and surficial deposits exposed in the Denali area span from the Paleozoic to the Quaternary. It is a structurally complex area that contains a history of rifting, accretion, and orogeny. There is evidence of multiple metamorphic events in the Mesozoic, mountain building in the Tertiary, and faulting in the present day. The region is the site of active faulting along one of the largest intra-continental fault systems, the Denali Fault system, which was the locus of a 7.9 M earthquake in 2002. This guidebook describes the key outcrops viewable along the Denali Park Road from the entrance to the Eielson Visitor Center, and along the Parks Highway from Healy to Cantwell.

Alaska↗
USGS1999

200,000 years of climate change recorded in eolian sediments of the High Plains of eastern Colorado and western Nebraska

Loess and eolian sand cover vast areas of the western Great Plains of Nebraska, Kansas and Colorado (Fig. 1). In recent studies of Quaternary climate change, there has been a renewed interest in loess and eolian sand. Much of the attention now given to loess stems from new studies of long loess sequences that contain detailed records of Quaternary glacial-interglacial cycles, thought to be a terrestrial equivalent to the foraminiferal oxygen isotope record in deep-sea sediments (Fig. 2). Loess is also a direct record of atmospheric circulation, and identification of loess paleowinds in the geologic record can test atmospheric general circulation models. Until recently, eolian sand on the Great Plains had received little attention from Quaternary geologists. The past decade has seen a proliferation of studies of Great Plains dune sands, and many studies, summarized below, indicate that landscapes characterized by eolian sand have had dynamic histories. On this field trip, we will visit some key eolian sand and loess localities in eastern Colorado and southwestern Nebraska (Fig. 1). Stratigraphic studies at some of these localities have been conducted for more than 50 years, but others have been systematically studied only in the past few years. Many of the data which appear in this guidebook have been derived from previous studies (Swinehart and Diffendal, 1990; Madole, 1994; Loope and others, 1995; Maat and Johnson, 1996; Muhs and others, 1996, 1997a, 1999; Mason and others, 1997; Aleinikoff and others, 1999), but some are presented here for the first time.

Colorado;Nebraska↗
USGS2006

A field guide to the central, creeping section of the San Andreas fault and the San Andreas Fault Observatory at Depth

This field trip is along the central section of the San Andreas fault and consists of eight stops that illustrate surface evidence of faulting, in general, and features associated with active fault creep, in particular. Fault creep is slippage along a fault that occurs either in association with small-magnitude earthquakes or without any associated large-magnitude earthquakes. Another aspect of the trip is to highlight where there are multiple fault traces along this section of the San Andreas fault zone in order to gain a better understanding of plate-boundary processes. The first stop is along the Calaveras fault, part of the San Andreas fault system, at a location where evidence of active fault creep is abundant and readily accessible. The stops that follow are along the San Andreas fault and at convenient locations to present and discuss rock types juxtaposed across the fault that have been transported tens to hundreds of kilometers by right-lateral motion along the San Andreas fault. Stops 6 and 7 are examples of recent studies of different aspects of the fault: drilling into the fault at the depth of repeating magnitude (M) 2 earthquakes with the San Andreas Fault Observatory at Depth (SAFOD) and the geological, geophysical, and seismological study of M 6 earthquakes near the town of Parkfield. Along with the eight official stops on this field trip are 12 “rolling stops”—sites of geologic interest that add to the understanding of features and processes in the creeping section of the fault. Many of the rolling stops are located where stopping is difficult to dangerous; some of these sites are not appropriate for large vehicles (buses) or groups; some sites are not appropriate for people at all. We include photographs of or from many of these sites to add to the reader's experience without adding too many stops or hazards to the trip. An extensive set of literature is available for those interested in the San Andreas fault or in the creeping section, in particular. For more scientifically oriented overviews of the fault, see Wallace ( 1990 ) and Irwin ( 1990 ); for a more generalized overview with abundant, colorful illustrations, see Collier ( 1999 ). Although the presence of small sections of the San Andreas fault was known before the great 1906 San Francisco earthquake, it was only after that event and subsequent geologic investigations reported in Lawson ( 1908 ) that showed the fault as a long structure, extending all the way from east of Los Angeles into northern California. Prentice ( 1999 ) described the importance of the 1908 “Lawson report” and how it pivotally influenced the understanding of the San Andreas. Hill ( 1981 ) presented a wonderful introduction to the evolution of thought on the San Andreas. Geologic maps and maps of the most recently active fault trace in the creeping section, or large parts of it, include those by Brown ( 1970 ), Dibblee ( 1971 , 1980 ), and Wagner et al. ( 2002 ); detailed geologic maps are discussed at various stops in this guide. Various aspects of the creeping section of the San Andreas fault have been the focus of many geologic field trips in the past few decades. Guidebooks for some of those trips include those by Gribi ( 1963a , 1963b ), Brabb et al. ( 1966 ), Rogers ( 1969 ), Bucknam and Haller ( 1989 ), Harden et al. ( 2001 ), and Stoffer ( 2005 ). The creeping section of the San Andreas fault zone lies between areas that experienced large-displacement surface breakage during great earthquakes in 1857 and 1906 (Fig. 1 inset). Burford and Harsh ( 1980 ) divided the creeping section into three segments: (1) a northwest section where the creep rate increases to the southeast in step-like increments, (2) a central section where the creep rate is relatively constant at a maximum value of ∼30 mm/yr (∼1.2 in/yr), and (3) a southeast section where the creep rate decreases to the southeast (Fig. 2 ). The rate of slip along the creeping section of the fault zone has been measured using creepmeters, alignment arrays, and laser distance-measuring devices. The aperture of measurements over which these measurements are made ranges from 10 m (∼33 ft) (creepmeters) to 100 m (∼330 ft) (alignment arrays) to kilometers and tens of kilometers (laser measuring devices). Creepmeter and alignment-array measurements are here termed “near-fault” measurements; laser measurements over distances of 1–2 km (∼0.6–1.2 mi) are termed “intermediate-scale” measurements; laser measurements over tens of kilometers (miles) are termed “broadscale” measurements. Comparisons among near-fault, intermediate-scale, and broadscale measurements and geologic maps show that the northwest part of the creeping section of the fault is composed of two narrow zones of active deformation, one along the San Andreas fault and one along the Calaveras-Paicines fault, whereas the central and southeast sections are both composed of a single relatively narrow zone of deformation. The southeast section is transitional to a locked zone southeast of Cholame; a locked fault is one that slips only in association with a moderate to large earthquake. Throughout the creeping section of the San Andreas fault zone, broadscale measurements generally indicate more deformation than near-fault and intermediate-scale measurements, which are in reasonably close agreement except at Monarch Peak (Mustang Ridge), near the center of the creeping section and our Stop 5 ((Figs. 1 ) and 2 ). Features that we see on this trip include offset street curbs, closed depressions (sag ponds), fault scarps (steep slopes formed by movement along a fault), a split and displaced tree, offset fence lines, fresh fractures, and offset road lines (Fig. 3 is a sketch showing some of the landforms that represent deformation by an active fault). We also see evidence of long-term maturity of the San Andreas fault, as indicated by fault features and displaced rock types (Fig. 4 ). Finally, we will visit sites of ongoing research into the processes associated with earthquakes and their effects. Discussions include drilling into the San Andreas fault at the SAFOD drill site and the 2004 Parkfield earthquake and its effects and implications.

California↗
USGS2006

Geology of Delaware Water Gap National Recreation Area, New Jersey-Pennsylvania

Many of the parks within the National Park System owe their uniqueness to their geologic framework. Their scenery is the result of diverse natural processes acting upon a variety of rocks that were deposited in varied environments in the geologic past. The Delaware Water Gap National Recreation Area (DEWA) contains a rich geologic and cultural history within its 68,714 acre boundary. Following the border between New Jersey and Pennsylvania, the Delaware River has cut a magnificent gorge through Kit-tantinny Mountain, the Delaware Water Gap, to which all other gaps in the Appalachian Mountains have been compared. Proximity to many institutions of learning in this densely populated area of the northeastern United States (Fig. 1 ) makes DEWA an ideal locality to study the geology of this part of the Appalachian Mountains. This one-day field trip comprises two stops within the gap itself and will include discussion on stratigraphy, structure, geomorphology, and glacial geology. The first stop will be at the bottom of the gap in Pennsylvania to look at the magnificent exposures in the cleft on the New Jersey side. This will be followed by a traverse to the top of Mount Tammany along a popular trail, where we will compare the geology across the river in Pennsylvania. Much of the information presented in this guidebook is summarized from Epstein (2001a , 2001b , 2001c ) and Epstein and Lyttle (2001) .

New Jersey, Pennsylvania↗
USGS2010

Teachers guide to geologic trails in Delaware Water Gap National Recreation Area, Pennsylvania–New Jersey

T he Delaware Water Gap National Recreation Area (DEWA) contains a rich geologic and cultural history within its 68,714 acre boundary. Following the border between New Jersey and Pennsylvania, the Delaware River has cut a magnificent gorge through Kittatinny Mountain, the Delaware Water Gap, to which all other gaps in the Appalachian Mountains have been compared. Proximity to many institutions of learning in this densely populated area of the northeastern United States (Fig. 1 ) makes DEWA an ideal locality to study the geology of this part of the Appalachian Mountains. This one-day field trip comprises an overview discussion of structure, stratigraphy, geomorphology, and glacial geology within the gap. It will be highlighted by hiking a choice of several trails with geologic guides, ranging from gentle to difficult. It is hoped that the “professional” discussions at the stops, loaded with typical geologic jargon, can be translated into simple language that can be understood and assimilated by earth science students along the trails. This trip is mainly targeted for earth science educators and for Pennsylvania geologists needing to meet state-mandated education requirements for licensing professional geologists. The National Park Service, the U.S. Geological Survey, the New Jersey Geological Survey, and local schoolteachers had prepared “The Many Faces of Delaware Water Gap: A Curriculum Guide for Grades 3–6” ( Ferrence et al., 2003 ). Copies of this guide will be given to trip participants and can be downloaded from the GSA Data Repository 1 . The trip will also be useful for instruction at the graduate level. Much of the information presented in this guidebook is modified from Epstein (2006) .

New Jersey, Pennsylvania↗
USGS2020

Foreward: Geology Field Trips in and around the U.S. Capital

The first annual meeting of the Geological Society of America (GSA) was held in 1888 in Ithaca, New York (Fairchild, 1932), but official Sections of GSA formed much later. During the spring of 1949, a symposium in Knoxville, Tennessee, on mineral resources of the southeastern United States became the catalyst for the creation of the Southeastern Section of the Geological Society of America (King, 1964), and the first annual meeting of the Southeastern Section was held in 1952 in Roanoke, Virginia (Wilson, 1954). The Northeastern Section formed much later, and its first annual meeting was held in 1966 in Philadelphia, Pennsylvania (Socolow, 1968). At all of these section meetings, field trips have been important venues for geologists and especially students to gather together, examine rocks in the field, and discuss ideas. These field trips have been especially important at combined section meetings because they provide settings for geologists who are experienced in one geographic region to examine and compare the geology of other regions. The first combined meeting of the Southeastern and Northeastern sections occurred in 1976 in Arlington, Virginia. Since then, the Southeastern and Northeastern sections have met together on numerous occasions, including 1982 in Washington, DC; 1991 in Baltimore, Maryland; 2004 in Tysons Corner, Virginia; and 2010 in Baltimore, Maryland. Since the first combined section meeting in 1976, there has been a gradual increase in the role of technology in geology field studies. In fact, during the past several decades there has been an increase in emphasis in our society on the instrumental component of science, the goal of which is operational techniques to do or control things, and a corresponding decrease in emphasis on the natural philosophy component of science, the goal of which is a greater understanding of the natural world (Dear, 2006). The modern education acronym STEM (Science, Technology, Engineering, and Mathematics), for example, is often used as a catch-all term that implies that science and technology are relatively synonymous, and implies that greater technology leads automatically to greater understanding of the natural world. This assumption, however, is not always valid (Dear, 2006), and technology should not be promoted as a substitute for field experiences. Technology can be a tool that leads to greater understanding of the natural world, but not all Science uses technology as a means of providing greater understanding. The benefits of new technologies include: (1) data of greater resolution; and (2) greater efficiency of capturing, storing, and visualizing data. The risks of new technologies include: (1) an overabundance of data, some of which may be of little value; (2) less time available for analysis of data, if geologists become occupied primarily with capturing and storing data; and (3) errors that arise from complacency and the perception that field-checking may not be necessary. In other words, there is a risk that a glut of data and vast amounts of time devoted to the capturing and storing of data may result in a reduced interest and (or) willingness to field-check data. In the spirit of the early GSA section meetings, we feel that there are still enormous advantages to conducting geology field trips in conjunction with traditional meeting presentations and posters. In 2020, with this current combined Southeastern and Northeastern section meeting in Reston, Virginia, we have assembled eight different field trips that cover a wide range of territory in and around the Nation’s capital. These field trip localities include the immediate vicinity of Washington, DC, as well as various locations in nearby areas of Virginia, Maryland, and West Virginia. The physiographic provinces include Mesozoic Rift Basins, the Piedmont, the Blue Ridge, the Valley and Ridge, and the Allegheny Plateau of the Appalachian Basin. The field trip sites exhibit a wide range of igneous, metamorphic, and sedimentary rocks, as well as rocks with a wide range of geologic ages from the Mesoproterozoic to the Holocene. We hope that this guidebook provides new motivation for geologists to examine rocks in the field, to discuss ideas with colleagues in the field, and to avoid becoming complacent. The editors of this volume would like to thank the authors of the different field trip guides, the field trip leaders, and all of the reviewers who made suggestions for improving the field trip manuscripts. The editors would also like to thank Elle Derwent of GSA for her logistical help and guidance regarding the field trips, and April Leo and the staff of the GSA Publications Department for seeing this book through to publication.

Maryland, Virginia, West Virginia↗
USGS2025

Stratigraphy, structure, and geomorphology of the central Appalachians across the North Mountain fault zone near Harrisonburg, Virginia, USA

This field trip focuses on the geology of the central Appalachian Valley and Ridge province near Harrisonburg, Virginia, USA. Recent geologic mapping utilizing 1-m resolution lidar data has revealed new insights into the Paleozoic stratigraphy, structural geology, and Neogene landscape evolution of the region. The detailed mapping reveals the presence of the Big Spring Station Member and multiple thrombolite zones in the Cambrian Conococheague Formation extending as far south as the Briery Branch 7.5 min quadrangle, providing insights into Late Cambrian sea-level fluctuations. Multiple outcrop exposures in the study area of this guidebook confirm recent work in Pennsylvania, USA, showing that the Ordovician Reedsville Shale overlies the Martinsburg Formation and that the two are distinct and mappable as separate formations rather than laterally equivalent units as previously interpreted. Our work extends the Silurian Williamsport Sandstone into Shenandoah County, Virginia, and describes its facies relationships with the Bloomsburg Formation along strike and across the Adams Run anticline. Mapping within the thick Devonian siliciclastic sequence reveals the presence of the Mahantango Formation on the western limb of Supin Lick syncline and illustrates its complex facies relationship with the Millboro Shale. In addition, we highlight new mapping criteria for the Brallier and Foreknobs Formations and demonstrate how the specific changes to the placement of the contact between them addresses previous challenges in their differentiation. We present cosmogenic burial ages of broad alluvial fan sediments in the Shenandoah Valley near Timberville and Briery Branch, Virginia, and erosion rates estimated for the Briery Branch stream basin. Both analyses provide new constraints on the timing of landscape evolution and karst development since the middle Pliocene. This field guide also highlights some significant structural features within the North Mountain fault zone, such as evidence of imbricated thrust sheets cut by cross-strike faults that have been exploited by Eocene igneous intrusions. Map-scale horses of Silurian and Ordovician rocks hold up ridges that are oblique to the regional strike. Deformation internal to one of these horse blocks is shown to be non-coaxial with respect to the main regional northwest directed transport.

Virginia↗
USGS2001

PHABSIM for Windows User's Manual and Exercises

This document is a combined self-study textbook and reference manual. The material is presented in the general order of a PHABSIM study placed within the context of an IFIM application. The document may also be used as reading material for a lecture-based course. This manual provides documentation of the various PHABSIM programs so every option of each program is treated. This text is not a guidebook for organization and implementation of a PHABSIM study. Use of PHABSIM should take place in the context of an IFIM application. See Bovee et al. (1998) for guidance in designing and performing a PHABSIM study as part of a larger IFIM application. The document concludes with a set of 12 laboratory exercises. Users are strongly encouraged to work through the laboratory exercises prior to applying the software to a study. Working through the exercises will enhance familiarity with the programs and answer many questions that may arise during a PHABSIM analysis.

Open-File Report↗
USGS2005

Bibliography of ground-water references for all 254 counties in Texas, 1886-2001

Preface This bibliography comprises more than 10,000 citations of ground-water references involving all 254 counties in Texas. The reference citations date from 1886 and extend into 2001. Publications and reports from more than 30 agencies, universities, water districts, geological societies, cities, consultants, and private publication outlets are included in the bibliography. The bibliographic listing is, first, alphabetical by county and, second, chronological by date of the report, from oldest to most recent. The passing years have seen a proliferation in both published and unpublished reports, and such proliferation continues to expand at an accelerating pace. All 254 counties have had groundwater studies, either cursory or detailed. Investigation and development of the ground-water resources of the State of Texas resulted in reports that appear in a variety of formats, including Federal, State, and local agency reports; scholarly, professional, and trade journals; conference proceedings; guidebooks; maps; and theses and dissertations. The end result for the person seeking ground-water information about specific Texas counties is the increasing difficulty in locating pertinent data among the many and diverse ground-water reports in which the information is recorded. This bibliography, covering a span of 115 years, should have considerable utility in guiding those individuals seeking ground-water information.

Texas↗
USGS1979

Implications of evaporites in the Upper Cambrian-Lower Ordovician Notch Peak Formation, southern House Range, western Utah

This report describes a preliminary study of some evaporites that occur in the Upper Cambrian part of the Notch Peak Formation in the southern House Range of western Utah (Taylor and Glanzman, 1979). The occurrences of halite and gypsum were first reported by James F. Miller in a guidebook article published in 1978. Miller implied a primary origin for the evaporites; that is, formation in association with the original depositional environment, but he did not study the deposits in detail.

Utah↗
USGS1996

Late Wisconsinan deglaciation styles of parts of the Contoocook, Souhegan, and Piscataquog drainage basins, New Hampshire

This report is the guidebook for the 56th annual meeting and field conference of the Friends of the Pleistocene, held May 22 and 23, 1993. Features were examined at 11 sites in the Contoocook, Souhegan, and Piscataquog Drainage Basins to illustrate the geologic history of this area, about 14,000 years ago, during the time of deglaciation. The Contoocook River Basin is the largest river basin that drains north in New Hampshire and is similar to northwardly draining parts of the Piscataquog and Souhegan River basins. During the retreat of the ice, the drainage divide between adjacent drainage basins acted as a dam and lakes formed behind it. As the ice continued to melt farther north, drainage outlets were uncovered at progressively lower altitudes along the drainage divide. This resulted in catastrophic draining of the lakes. Evidence for the existence of the lakes includes fine-grained lake-bottom deposits and deltas at successively lower elevations. Geomorphic evidence for the catastrophic draining includes Pulpit Rock in Bedford, N.H. and V-shaped notches eroded into till and bedrock. In Henniker, N.H., further evidence of catastrophic draining of a large lake in the Contoocook River Basin is a combination alluvial fan and delta that formed when rapidly draining lake water flowed across a till slope, eroded the till, and redeposited the material where it entered a smaller, much lower lake.

Open-File Report↗
USGS1997

Annotated bibliography of selected publications, through 1996, Cheyenne municipal well field areas, Cheyenne, Wyoming

Annotated bibliographies for 55 hydrology and geology manuscripts pertaining to the Cheyenne municipal wells fields are listed in this report. For each manuscript, a citation is provided, a summaryparagraph is presented, key words are listed, and a location of the report is given. The report lists manuscripts, conference proceedings, and guidebooks published by the U. S. Geological Survey, State of Wyoming, Geological Society of America, Wyoming State Geological Survey, private consultants, and University of Wyoming. Information on geological formations, structural geology, aquifer characteristics, water levels, well- field production, water-demand projections, and water quality is included in the manuscripts. The Cheyenne Board of Public Utilities, the University of Wyoming, and the U. S. Geological Surveycooperatively produced this annotated bibliography to allow easy access and efficient utilization of existing data. The manuscripts were authored between 1910 and 1996, reflecting work completed over a long period of development in the Cheyenne, Wyoming area. Some manuscripts did not receive broad distribution and indexing, thus they have been difficult to locate in the past. By having the references and summaries within one report, time and effort to gather previous study results will be minimized.

Wyoming↗
USGS2025

Bedrock geologic map of the Bellows Falls 7.5- x 15-minute quadrangle, Windham and Windsor Counties, Vermont, and Sullivan and Cheshire Counties, New Hampshire

Introduction The bedrock geology of the Bellows Falls 7.5- x 15-minute quadrangle, Vermont and New Hampshire, consists of polydeformed Ordovician to Devonian metasedimentary, metavolcanic, and metaplutonic rocks of the Connecticut Valley trough, Bronson Hill anticlinorium (or Bronson Hill terrane), and the Central Maine terrane. Previous work in this area includes a 1:62,500-scale published map and text (1946), State geologic maps of New Hampshire (1997) and Vermont (2011), and various maps and reports presented largely as parts of field trip guidebooks. A provisional open-file map of the geology of the Vermont part of the Bellows Falls 7.5- x 15-minute quadrangle, completed in 1997, is incorporated and revised on this map based on additional fieldwork. This study recognizes three major structural levels from west to east and from lowest to highest: (1) autochthonous rocks of the Connecticut Valley trough; (2) allochthonous rocks of the New Hampshire sequence and Bronson Hill arc in the Monroe thrust sheet (or nappe), including the Skitchewaug nappe; and (3) allochthonous rocks of the Fall Mountain thrust sheet or nappe.

New Hampshire, Vermont↗
USGS2017

Field-trip guides to selected volcanoes and volcanic landscapes of the western United States

The North American Cordillera is home to a greater diversity of volcanic provinces than any comparably sized region in the world. The interplay between changing plate-margin interactions, tectonic complexity, intra-crustal magma differentiation, and mantle melting have resulted in a wealth of volcanic landscapes. Field trips in this guide book collection (published as USGS Scientific Investigations Report 2017–5022) visit many of these landscapes, including (1) active subduction-related arc volcanoes in the Cascade Range; (2) flood basalts of the Columbia Plateau; (3) bimodal volcanism of the Snake River Plain-Yellowstone volcanic system; (4) some of the world’s largest known ignimbrites from southern Utah, central Colorado, and northern Nevada; (5) extension-related volcanism in the Rio Grande Rift and Basin and Range Province; and (6) the eastern Sierra Nevada featuring Long Valley Caldera and the iconic Bishop Tuff. Some of the field trips focus on volcanic eruptive and emplacement processes, calling attention to the fact that the western United States provides opportunities to examine a wide range of volcanological phenomena at many scales. The 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) in Portland, Oregon, was the impetus to update field guides for many of the volcanoes in the Cascades Arc, as well as publish new guides for numerous volcanic provinces and features of the North American Cordillera. This collection of guidebooks summarizes decades of advances in understanding of magmatic and tectonic processes of volcanic western North America. These field guides are intended for future generations of scientists and the general public as introductions to these fascinating areas; the hope is that the general public will be enticed toward further exploration and that scientists will pursue further field-based research.

Scientific Investigations Report↗
USGS2018

Geologic field-trip guide of volcaniclastic sediments from snow- and ice-capped volcanoes—Mount St. Helens, Washington, and Mount Hood, Oregon

This field guide for the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly 2017 focuses on volcaniclastic sediments from Mount St. Helens in Washington and Mount Hood in Oregon. The trip spends four days in the field and includes nine stops at each volcano. For completeness, this guidebook also includes sixteen optional stops in the Mount St. Helens area and three in the Mount Hood area. These two volcanoes provide excellent depositional records of the broad spectrum of volcanic hazards that involve the flow or fall of volcaniclastic particles. At the field-trip stops we will contrast and compare the different types of deposits—sediments that can be frustratingly difficult to distinguish from one another. Correct identification of deposit origin leads to a better understanding of hazards that can impact vulnerable communities at particular volcanoes. During this four-day field trip, we will spend two days in the Mount St. Helens area and two days near Mount Hood. On the first day, we will visit debris-avalanche and lahar deposits in the Toutle River valley in Washington. The second day will focus on pyroclastic density current, pyroclastic-fall, lahar, and volcano-fluvial deposits in the Lewis River drainage system near Mount St. Helens. On the third day, we will visit hyaloclastites, glacial tills, and other diamicts in the Hood River and Sandy River basins near Mount Hood. The fourth and final day will focus on distal lahar and volcano-fluvial deposits downstream of Mount Hood. What follows is an in-depth introduction to the deposits studied on this field trip. We provide criteria that are observable in the field to aid in differentiating between pyroclastic density current, pyroclastic-fall, debris-avalanche, lahar, water-flood, and glacial deposits. We also introduce the Holocene eruptive histories of Mount St. Helens and Mount Hood and discuss the processes responsible for deposit emplacement. Field-trip stops and features of interest along the route are described in detail in a road log that provides daily cumulative mileage.

Oregon, Washington↗
USGS2017

Overview for geologic field-trip guides to volcanoes of the Cascades Arc in northern California

The California Cascades field trip is a loop beginning and ending in Portland, Oregon. The route of day 1 goes eastward across the Cascades just south of Mount Hood, travels south along the east side of the Cascades for an overview of the central Oregon volcanoes (including Three Sisters and Newberry Volcano), and ends at Klamath Falls, Oregon. Day 2 and much of day 3 focus on Medicine Lake Volcano. The latter part of day 3 consists of a drive south across the Pit River into the Hat Creek Valley and then clockwise around Lassen Volcanic Center to the town of Chester, California. Day 4 goes from south to north across Lassen Volcanic Center, ending at Burney, California. Day 5 and the first part of day 6 follow a clockwise route around Mount Shasta. The trip returns to Portland on the latter part of day 6, west of the Cascades through the Klamath Mountains and the Willamette Valley. Each of the three sections of this guidebook addresses one of the major volcanic regions: Lassen Volcanic Center (a volcanic field that spans the volcanic arc), Mount Shasta (a fore-arc stratocone), and Medicine Lake Volcano (a rear-arc, shield-shaped edifice). Each section of the guide provides (1) an overview of the extensive field and laboratory studies, (2) an introduction to the literature, and (3) directions to the most important and accessible field localities. The field-trip sections contain far more stops than can possibly be visited in the actual 6-day 2017 IAVCEI excursion from Portland. We have included extra stops in order to provide a field-trip guide that will have lasting utility for those who may have more time or may want to emphasize one particular volcanic area.

California↗
USGS2022

Field-trip guide to continental arc to rift volcanism of the southern Rocky Mountains—Southern Rocky Mountain, Taos Plateau, and Jemez Mountains volcanic fields of southern Colorado and northern New Mexico

The southern Rocky Mountains of northern New Mexico and southern Colorado preserve the Oligocene to Pleistocene record of North American continental arc to rift volcanism. The 35–23 million year old (Ma) southern Rocky Mountain volcanic field (SRMVF), spectacularly preserved in the San Juan Mountains of southern Colorado, records the evolution of large andesitic stratovolcanoes to complex caldera clusters, from which at least 22 major ignimbrite sheets (each 150–5,000 cubic kilometers) were erupted. Outflow deposits of the SRMVF preserved along the broadly uplifted northwest flank of the northern Rio Grande rift basin (the San Luis Valley) provide critical structural and temporal constraints on the inception of crustal extension. Coincident with waning stages of SRMVF caldera-forming volcanism (~25.4 Ma), extensional tectonism was accompanied by a transition from bimodal early Miocene to intermediate-composition late Miocene and dominantly basaltic Pliocene rift volcanism of the Taos Plateau in the southern San Luis Basin. Concomitant rift volcanism in the Española Basin and bordering Jemez Mountains of northern New Mexico records a similar Miocene eruptive history dominated by intermediate-composition volcanism that transitioned locally to Pliocene rift-related basaltic volcanism of the Cerros del Rio volcanic field and culminated in eruptions of the iconic rhyolitic Pleistocene Bandelier Tuff and formation of the Valles Caldera along the northwestern rift-basin margin. This 6-day, 7-night field trip will focus, in broadly equal proportions, on rift-related extensional volcanism of the Jemez Mountains and Taos Plateau regions during the first half of the trip, and on caldera-forming volcanism of the southern Rocky Mountain volcanic field during the second half of the trip. The 35-million-year volcanic history of the region highlighted by new geologic mapping, high-resolution geochronology, petrologic, geochemical, and geophysical data facilitates discussion of (1) the magmatic response to the tectonic transition from subducted-slab arc to continental-rift volcanism; (2) the nature and temporal evolution of rift magmas; (3) fault controls on the spatial evolution of rift magmatism; (4) the diversity of continental-arc ignimbrite volcanism and associated lavas; (5) ignimbrite caldera structure and associated intrusions in three-dimension; (6) the role of recycled crystal mush and magmatic cumulates during growth of Cordilleran batholiths; and (7) high-precision geochronologic contributions to interpretation of relations between regional tectonic and volcanic processes. Most stops will be along roads, but there will be moderate hikes on trails of less than 1-hour duration covering 1–2 kilometers (0.6–1.2 miles) with modest elevation gain of <150 meters (<492 feet). The route will progress in reverse stratigraphic order, starting in the Jemez Mountains of New Mexico and proceed northward to San Luis Basin and San Luis Hills before turning west to the southeast and central San Juan Mountains. Our last full day takes us to the little-visited and only recently mapped, Bonanza caldera of the northeastern San Juan Mountains and on the final day, we leave the San Luis Valley to briefly explore the Tertiary subvolcanic plutons of the Collegiate Range along the west side of the Arkansas Valley rift valley, en route to Denver. The authors of all daily contributions acknowledge the helpful reviews by Amy Gilmer and Joe Colgan and thank Christine Chan and Jeremy Havens for assistance with figures, tables, and guidebook text.

Colorado, New Mexico↗