Sponsor
Portland State University. Department of Geology
First Advisor
Marvin H. Beeson
Term of Graduation
Fall 1986
Date of Publication
11-12-1986
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Geology
Department
Geology
Language
English
Subjects
Geology -- Oregon, Geology -- Cascade Range
DOI
10.15760/etd.5543
Physical Description
1 online resource (2, vi, 118 pages)
Abstract
The Willamette Pass area is situated at the intersection of two hypothesized structural features, the Western Cascade-High Cascade boundary and the Eugene-Denio lineament. It is of interest due to its designation by the U.S. Department of the Interior as a Known Geothermal Resource Area.
Volcanic rocks of Oligocene to Pleistocene age are exposed in the study area. The oldest rocks are the Oligocene-Miocene lavas, undifferentiated, which are a diverse unit of ignimbrites and intermediate to silicic flows. The Oligocene-Miocene rhyodacites are a stratigraphically equivalent unit which is predominantly composed of aphyric rhyodacite flows. Middle Miocene volcanism produced the basaltic lavas of Tumblebug Creek and the andesitic lavas of Moss Mountain. The predominantly basaltic and basaltic andesite High Cascade volcanism began around 5.5 m.y.B.P. and continued into the Pleistocene.
Uplift of the Western Cascade Range occurred between 4.32 and 1.98 m.y.B.P. and is marked in the stratigraphic record by an unconformity present in most of the study area. The unconformity becomes difficult to recognize in the eastern portion of the study area. It is possible that the southern extension of the north-trending Waldo Lake fault extends into the eastern part of the study area and is the structure that accommodated Western Cascades uplift.
Reevaluation of the Groundhog Creek lineament has led to the conclusion that it could be caused by homoclinal folding. Faulting is not recognized in middle Miocene rocks along the lineament, but is equivocal in underlying rocks.
Northwest-trending faults were not found along the trend of the northwest-trending Eugene-Denio lineament.
Rights
In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
Persistent Identifier
https://archives.pdx.edu/ds/psu/20639
Recommended Citation
Woller, Neil M., "Geology of the Willamette Pass Area, Cascade Range, Oregon" (1986). Dissertations and Theses. Paper 3655.
https://doi.org/10.15760/etd.5543
Plate A
woller plate b.jpg (1028 kB)
Plate B
woller_geology_of_the_willamette_pass_area.jpg (909 kB)
Geology of the Willamette Pass Area
Comments
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