Geological Survey Circular 838 Guides to Some Volcanic Terrances in Washington, Idaho, Oregon, and Northern California

Cover

COVER PHOTOGRAPH: Big Obsidian Flow, Newberry Volcano, central Oregon (Photograph courtesy of Travel Section of Oregon, Department of Transportation)

Preface

David Alexander Johnston

Guide to geologic field trip between Lewiston, Idaho, and Kimberly, Oregon, emphasizing the Columbia River Basalt Group by D. A. Swanson, U.S. Geological Survey, Menlo Park, California 94025; and T. L. Wright, U.S. Geological Survey, Reston, Virginia 22092

Figure
1. Index map with extent of Columbia River Basalt Group
2. Chart of stratigraphy, age, magnetic polarity, and chemical type, Columbia River Basalt Group
3. Maps showing distribution, feeder dikes of four formations in Columbia River Basalt Group
4. Stratigraphic section near Pomeroy, Washington
5. Maps showing distribution, feeder dikes of four members in two formations of Columbia River Basalt Group
6. Idealized cross section of flow in Yakima Basalt Subgroup

Table
1. Major-element compositions of chemical types, Columbia River Basalt Group
2. Trace-element compositions of chemical types, Yakima Basalt Subgroup

Roadlog for geologic field trip between Lewiston, Idaho, and Kimberly, Oregon by D. A. Swanson, U.S. Geological Survey, Menlo Park, CA 94025; and T. L. Wright, U.S. Geological Survey, Reston, VA 22092

Figure
1. Map of field trip stops

Guide to geologic field trip between Kimberly and Bend, Oregon with emphasis on the John Day Formation by Paul T. Robinson, Department of Earth Sciences, University of California, Riverside, CA 92521; and Gerald F. Brem, Department of Earth Sciences, California State University, Fullerton, CA 92634

Figure
1. Index map of north-central Oregon with extent of John Day Formation
2. Stratigraphic columns, western and eastern John Day Formation

Table
1. Modal analyses of John Day rocks
2. Chemical composition, fresh and altered welded tuff
3. Chemical analysis, least altered John Day ash-flow tuffs
4. Average composition of mafic lava flows

Roadlog for geologic field trip between Kimberly and Bend, Oregon, with emphasis on the John Day Formation by Paul T. Robinson, Department of Earth Sciences, University of California, Riverside, CA 92521

Figure
3. Map of field trip stops

Central High Cascade roadside geology, by Edward M. Taylor, Department of Geology, Oregon State University

Figure
1. Index map
2. Diagrammatic cross section of Cascades and Deschutes Basin

Roadlog for Central High Cascade geology, Bend, Sisters, McKenzie Pass, and Santiam Pass, Oregon by Edward M. Taylor, Department of Geology, Oregon State University

Figure
3. Geologic sketch map, mile 0.0 to 16.6
4. Geologic sketch map, mile 16.6 to 27.1
5. Geologic sketch map, mile 27.1 to 34.5 to 44.6
6. Geologic sketch map, mile 44.6 to 57.9
7. Geologic sketch map, mile 57.9 to 72.3
8. Geologic sketch map, mile 72.3 to 83.5
9. Geologic sketch map, mile 83.5 to 91.6 to 99.8
10. Geologic sketch map, mile 99.8 to 119.0
11. Geologic sketch map, mile 119.0 to 129.1
12. Geologic sketch map, mile 129.1 to 142.0

Newberry Volcano, Oregon by Norman S. MacLeod, David R. Sherrod, U. S. Geological Survey, Menlo Park, CA 94025; Lawrence A. Chitwood, U.S. Forest Service, Bend, OR 97701; and Edwin H. McKee, U. S. Geological Survey, Menlo Park, CA 94025

Figure
1. Geologic sketch map of Newberry Volcano
2. Geologic sketch map of Newberry caldera

Table
1. Representative chemical analyses of Newberry rocks

Roadlog for Newberry Volcano, Oregon, by Norman S. MacLeod, David R. Sherrod, U. S. Geological Survey, Menlo Park, CA 94025; Lawrence A. Chitwood, U.S. Forest Service, Bend, OR 97701; and Edwin H. McKee, U. S. Geological Survey, Menlo Park, CA 94025

High Lava Plains, Brothers fault zone to Harney Basin, Oregon by George W. Walker, U. S. Geological Survey, Menlo Park, CA 94025, and Bruce Nolf, Central Oregon Community College, Bend, Oregon

Figure
1. Index map showing High Lava Plains and Harney Basin
2A, B, C. Route map with major structural elements and rhyolite K/Ar ages
3. Map of basalt fields

Table
1. Compositions of selected basalts and rhyolites

Roadlog for High Lava Plains, Brothers fault zone to Harney Basin, Oregon, by George W. Walker, U. S. Geological Survey, Menlo Park, CA 94025, and Bruce Nolf, Central Oregon Community College, Bend, Oregon

A field trip to the maar volcanoes of the Fort Rock—Christmas Lake Valley basin, Oregon, by G. H. Heiken, Geosciences Division, Los Alamos Scientific Laboratory, Los Alamos, NM 87545; R. V. Fisher, Department of Geology, University of California, Santa Barbara, CA 93106; and N. V. Peterson, State of Oregon, Department of Geology and Mineral Industries, Grants Pass, OR 97526

Figure
1. Location map
2. Map of Fort Rock—Christmas Lake Valley Basin, showing route of field trip
3. Cross sections through Moffitt Butte, Klamath County, Oregon
4. Photograph of maar deposits, Big Hole
5. Map of Hole-in-the-Ground
6. Geologic section through Hole-in-the-Ground
7. Fort Rock tuff ring: map, photograph, cross section
8a. Map of Table Rock tuff ring complex
8b. Stratigraphic section of sediments under Table Rock tuff ring complex
9. Diagram of sediment-tuff-breccia contact, Table Rock tuff ring complex
10. Sketch of cliff showing vent 8, Table Rock tuff ring complex
11. Diagram showing palagonitization of tuff, Table Rock maar complex
12. Map and cross sections of vents 4 and 5, Table Rock tuff ring complex
13. Sketch and map of vent 5, Table Rock tuff ring complex
14. Stratigraphic section, Table Rock tuff cone
15. Cross section, Table Rock
16. Sketch and map of vent 9, Table Rock tuff ring complex
17. Slump structure in tuff ring 1, Table Rock, and sketches showing its formation

Table
1. Chemical analyses of basalts, Fort Rock—Christmas Lake Valley Basin

Roadlog for field trip to Medicine Lake Highland by Julie M. Donnelly-Nolan, U.S. Geological Survey, MS-18, 345 Middlefield Road, Menlo Park, CA 94025; Eugene V. Ciancanelli, Cascadia Exploration Corporation, 3358 Apostal Road, Escondido, CA 92025; John C. Eichelberger, Geological Research G-6, Los Alamos Scientific Laboratory, Los Alamos, NM 87545; Jon H. Fink, Geology Department, Stanford University, Stanford, CA 94305; and Grant Heiken, Geological Research G-6, Los Alamos Scientific Laboratory, Los Alamos, NM 87545

Figure
1. Location map for field trip to Medicine Lake Highland

Captain Jack's Stronghold (The geologic events that created a natural fortress) by Aaron C. Waters, 308 Moore Street, Santa Cruz, CA 95060. Map by David Kimbrough and Aaron C. Waters

Figure
1. Map of Captain Jack's Stronghold

Pre-Holocene silicic volcanism on the northern and western margins of the Medicine Lake Highland, California by Stanley A. Mertzman, Department of Geology, Franklin and Marshall College, Lancaster, PA 17604

Figure
1. Geologic map of selected units, Medicine Lake Highland

Table
1. Analytical results of K—Ar dating
2. Chemical analyses of the Andesite Tuff
3. Chemical analyses of the lava flow equivalent of the Andesite Tuff and of older silicic rocks
4. Modal analyses of the Andesite Tuff
5. Chemical analyses of three Holocene glass flows

Surface structure of Little Glass Mountain by John H. Fink, Geology Department, Stanford University, Stanford CA 94305 (Present address: Department of Geology, Arizona State University, Tempe, AZ 85281)

Figure
1. Schematic cross section through a rhyolitic obsidian flow
2. Flow front, Little Glass Mountain: photo, foliations, interpretation
3. Map of part of northeast lobe, Little Glass Mountain
4. Compressional folds in flow front, Little Glass Mountain
5. Diagram of diapir rise in rhyolitic obsidian flow
6. Map of part of northwest lobe, Little Glass Mountain
7. Map of large ridge, northwest lobe
8. Photo, part of northwest lobe, Little Glass Mountain

Holocene plinian tephra deposits of the Medicine Lake Highland, California, by Grant Heiken, Los Alamos Scientific Laboratory, Geosciences Division, Los Alamos, NM 87545

Figure
1. Map of deposits <1100 years old, Medicine Lake Highland
2. Isopach map of Little Glass Mountain and Glass Mountain tephra
3. Correlation of Little Glass Mountain tephra units

Table
1. Age relations of Holocene volcanic deposits, Medicine Lake Highland

Mechanism of magma mixing at Glass Mountain, Medicine Lake Highland volcano, California, by John C. Eichelberger, Geosciences Division, University of California, Los Alamos Scientific Laboratory, Los Alamos, NM 87545

Figure
1. Map of Glass Mountain sample locations and lithologic units
2. Map showing distribution of Holocene lavas, Medicine Lake Highland
3. Cross section through Medicine Lake Highland volcano
4. Photomicrographs of basaltic xenolith in Glass Mountain rhyodacite, shown in reflected light, transmitted light, and crossed polars
5. Graph of density versus pressure, Glass Mountain materials
6. Sketches of probable eruptive sequence at Glass Mountain

Table
1. Densities of Glass Mountain samples

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UNITED STATES DEPARTMENT OF THE INTERIOR
JAMES G. WATT, Secretary

GEOLOGICAL SURVEY
H. William Menard, Director

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