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Date Permissions Signed


Date of Award

Spring 1981

Document Type

Masters Thesis

Degree Name

Master of Science (MS)



First Advisor

Suczek, Christopher A., 1942-2014

Second Advisor

Vance, Joseph A., 1930-

Third Advisor

Pevear, David R.


Upper Eocene to lower Oligocene sedimentary rocks in the Lake McMurray area of Skagit County, Washington, consist of approximately 1500 m of conglomerate, sandstone, shale, and siltstone which were deposited in fluvial and marine environments along the continental margin. These rocks are known as the rocks of Bulson Creek.

Two main lithofacies can be recognized within the sequence: the lowest is nonmarine and consists of poorly sorted, thick, and structureless conglomerate with interbedded sandstone, siltstone, shale, and minor coal lenses; the upper lithofacies grades from a transitional nonmarine facies to a shallow water marine facies that consists of well sorted, fossiliferous pebbly sandstone, sandstone, and siltstone. The lower lithofacies rocks lie unconformably on paleosols developed on pre-Tertiary rocks. The upper lithofacies rocks lie unconformably over the lower lithofacies rocks.

At least three periods of tectonism and two periods of deposition are recognized. The Devils Mountain fault is a major east-west trending structural feature along which there has been a long and complex history of motion. The deformation of the rocks in the Lake McMurray area can be attributed to movement along this fault, which forms the northern border along which the Bulson Creek rocks crop out. Deposition of the lower lithofacies rocks followed compressional folding associated with normal faulting. These rocks were folded prior to the deposition of the upper lithofacies, as is evident by the angular unconformity between the two units. Normal faulting along the Devils Mountain fault tilted these units to the south.




Bulson Creek, Rocks of Bulson Creek, Sedimentary rocks



Western Washington University

OCLC Number


Subject – LCSH

Sedimentary rocks; Geology, Structural; Geology, Stratigraphic--Eocene; Geology, Stratigraphic--Oligocene; Petrology--Washington (State)--Skagit County

Geographic Coverage

Skagit County (Wash.)




masters theses




Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.

Geologic Map of the Lake McMurray Area Washington reduced 7272144.pdf (711 kB)
Geologic Map of the Lake McMurray Area, Washington

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