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U.S. Geological Survey
Geologic Investigations Series I-2538
Online version 1.0

Geologic Map of the Snoqualmie Pass 30 x 60 Minute Quadrangle, Washington


R.W. Tabor, V.A. Frizzell, Jr., D.B. Booth, and R.B. Waitt

Sonqualmie Pass

Looking north from the Cascade Crest near Arch Rock. Light-colored beds in foreground are well-bedded volcanic-clastic rocks of the Miocene Fifes Peak Formation (unit Tfv). Dark andesitic flows of the Fifes Peak (Tf) are beyond. The highest peak on the right skyline is Mount Stuart (9,415 ft). Ridges between Mount Stuart and the Fifes Peak outcrops are carved from volcanic rocks of the mostly Eocene Naches Formation.

Fir-covered flats beyond the bedded Fifes Peak outcrop are in the vicinity of Naches Pass. On the skyline beyond that is Mount Daniel, a Tertiary volcanic complex, possibly correlative with the Oligocene Ohanepecosh Formation. West of Mount Daniel, sharply pointed peaks are in the Chimney Rock-Overcoat Peak area and are underlain by thermally metamorphosed Naches volcanic rocks.


The Snoqualmie Pass quadrangle lies at the north edge of a Tertiary volcanic and sedimentary cover, where the regional structural uplift to the north elevated the older rocks to erosional levels. Much of the quadrangle is underlain by folded Eocene volcanic rocks and fluvial deposts of an extensional event, and these rocks are overlain by Cascade arc volcanic rocks: mildly deformed Oligocene-Miocene rocks and undeformed younger volcanic rocks. Melanges of Paleozoic and Mesozoic rocks are exposed in structural highs in the northern part of the quadrangle. The quadrangle is traversed north to south by the Straight Creek Fault, and the probably partially coincident Darringon-Devils Mountain Fault. A rich Quaternary stratigraphy reveals events of the Frazer glaciation.

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Jump to USGS Data Series 186: Database for the Geologic Map of the Snoqualmie Pass 30-Minute by 60-Minute Quadrangle, Washington (I-2538)

For questions about the content of this report, contact Rowland Tabor

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USGS Information Services, Box 25286,
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telephone: 888-ASK-USGS; e-mail:

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Maintained by: Michael Diggles
Created: April 17, 2001
Last modified: May 18, 2006 (mfd)