Aerial photograph of Port Discovery located in the extreme northeast corner of the Uncas quadrangle. The slopes surrounding the port are mantled with Late Pleistocene glacial till of the Vashon Stade of the Fraser Glaciation. This material covers the underlying Tertiary Sandstone of Snow Creek, a sandstone and silty sandstone turbidite deposit, and the Lower and Middle Eocene Crescent Formation basalt. Photograph courtesy of Washington State Department of Ecology.
The Uncas quadrangle in the northeastern Olympic Peninsula covers the transition from the accreted terranes of the Olympic Mountains on the west to the Tertiary and Quaternary basin fills of the Puget Lowland to the east. The relief of the map area ranges from sea level at Port Discovery to 4116 feet on the flank of the Olympic Mountains to the southwest. Previous geologic mapping within and marginal to the Uncas quadrangle includes Cady and others in 1972, Brown and others in 1960, Tabor and Cady in 1978, Yount and Gower in 1991, and Yount and others in 1993. Paleontologic and stratigraphic investigations by University of Washington graduate students under Allison in 1959; Thoms in 1959; Sherman in 1960; Hamlin in 1962; and Spencer in 1984 also encompass parts of the Uncas quadrangle. Geologic mapping for this report was conducted in February 1998 by Haeussler and Wells following preliminary mapping by Yount in 1976 and 1979. The description of surficial map units follows Yount and others in 1993 and Booth and Waldron in 1998. Bedrock map units are modified from Yount and Gower's paper in 1991 and Spencer in 1984. Geologic time scale is that of Berggeren and others 1995 paper.
The Uncas quadrangle lies in the forearc of the Cascadia subduction zone, 10 km east of the Cascadia accretionary complex exposed in the core of the Olympic Mountains. Underthrusting of the accretionary complex beneath the forearc has uplifted and tilted to the east the Coast Range basalt basement and overlying marginal basin strata, which comprise most of the Uncas quadrangle. The Eocene submarine and subaerial tholeiitic basalt of the Crescent Formation on the Olympic Peninsula is thought to be the exposed mafic basement of the Coast Range, an oceanic terrane accreted to the margin in Eocene time. The Coast Range basalt terrane may have originated as an oceanic plateau or by oblique marginal rifting, but its subsequent emplacement history is complex. In southern Oregon, onlapping strata constrain the suturing to have occurred by 50 Ma. However, on southern Vancouver Island where the terrane bounding Leech River fault is exposed, Brandon and Vance in 1992 concluded suturing to North America occurred in the broad interval between 42 and 24 Ma. After emplacement of the Coast Range basalt terrane, the Cascadia accretionary wedge developed by frontal accretion and underplating. Domal uplift of the part of the accretionary complex beneath the Olympic Mountains occurred after ~18 million years ago. Continental and alpine glaciation during Quaternary time has reshaped the growing topography of the Olympic Mountains.
Reduced image of the Uncas 7.5 minute quadrangle geologic map
Files available for downloading:
Download the Suggested citation and version History of this report (4 kb).
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For those users who do not have access to a plotter, a set of page-sized PDFs is provided below. The text file (of99-421-text.pdf) and the Description of Map Units (DMU) file (of99-421-dmu.pdf) can be viewed and printed as is. The map file (of99-421-map.pdf) consists of eight panels that must be cut and pasted together with pages 1-4 being the left column from top to bottom and pages 5-8 being the right column from top to bottom.
Download the text file of of99-421 (83 kb).
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Arc-export files
Download uncas.aml - aml file to recreate geologic map (4 kb).
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Download uncasstrc.e00 - structural data coverage (165 kb).
Related files
If needed, other line, shade, and marker sets are available here.
Metadata
Download the Metadata in text format (16 kb).
Download the Metadata in HTML format (23 kb).
Download the Metadata in "FAQ" format (19 kb).
Culture/topography files
Digital Raster Graphic (DRG) georeferenced files covering the study area
can be downloaded from here:
Download uncasdrg.tfw - as a Word file for georeferencing (17 kb).
Download uncasdrg.tif - digital raster graphic (DRG) of Uncas quadrangle (6.1 MB).
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For questions about the scientific content of this report, please contact: Peter Haeussler
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Created: September 29, 1999 (cad)
Updated: October 18, 2007 (bwr, mfd)
