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Geologic map of the North Cascade Range, Washington


Geologic map of the Skykomish River 60-minute by 30- minute quadrangle, Washington

U.S. Geological Survey Miscellaneous Investigations Map I-1963, scale 1:100,000, 1993

by R.W. Tabor, V.A. Frizzell Jr., D.B. Booth, R.B. Waitt, J.T. Whetten, and R.E. Zartman

Generalized geologic map of the Skykomish River Quadrangle.
Click here for enlarged version with explanation (60K).

Thumbnail of generalized geologic map of the Skykomish River quadrangle


From the easternmost edges of suburban Seattle, the Skykomish River quadrangle stretches east across the low rolling hills and broad river valleys of the Puget Lowland, across the forested foothills of the North Cascades, and across high meadowlands to the bare rock peaks of the Cascade crest. The quadrangle straddles parts of two major river systems, the Skykomish and the Snoqualmie Rivers, which drain westward from the mountains to the lowlands.

In the late 19th Century mineral deposits were discovered in the Monte Cristo, Silver Creek and the Index mining districts within the Skykomish River quadrangle. Soon after came the geologists: Spurr (1901) studied base- and precious-metal deposits in the Monte Cristo district and Weaver (1912a) and Smith (1915, 1916, 1917) in the Index district. General geologic mapping was begun by Oles (1956), Galster (1956), and Yeats (1958a) who mapped many of the essential features recognized today. Areas in which additional studies have been undertaken are shown on sources of data maps. Our work in the Skykomish River quadrangle, the northwest quadrant of the Wenatchee 1 X 2 degree quadrangle, began in 1975 and is part of a larger mapping project covering the Wenatchee quadrangle.

Tabor, Frizzell, Whetten, and Booth have primary responsibility for bedrock mapping and compilation. Zartman carried out the zircon uranium-thorium-lead (U-Th-Pb) isotopic analyses and advised in the interpretation of isotope ages. Booth mapped most of the unconsolidated deposits of the western half of the quadrangle. Waitt mapped most of the unconsolidated deposits of the eastern half; in the eastern two-thirds of the map area, mostly along the crest of the mountains, talus and other morphologically distinct surficial units were mapped primarily from aerial photographs. Details of the unconsolidated deposits in the western half of the map are shown on a separate map (Booth, 1990).

Our field work was helped considerably by Eduardo Rodriguez (1975), Bill Gaum and Kim Marcus (1977), Sam Johnson, Brett Cox, Elizabeth Lincoln Mathieson and Nora Shew (1978), P. Thompson Davis (1979), M. Jean Hetherington and Joe Marquez (1979-80), Jim Talpey, Paul Carroll, and Kathy Lombardo (1979), Steve Connelly, Stephen A. Sandberg, Susan Cook, Fredrika Moser, and Fred Beall (1981). Jean Hetherington, Steve Connelly, Kathleen Ort, and Fred Zankowsky helped in the office and laboratory. Dennis H. Sorg supplied clean mineral concentrates for radiometric dating.

We thank Robert Kenlee, of Converse Ward Davis and Dixon, and Arthur Arnold, of Bechtel and Associates, for supplying drill-hole data and reports related to the City of Everett's Spada Lake projects. Curtis Scott, of Bechtel, showed us many interesting features in the Blue Mountain water diversion tunnel.

Doug Bucklew (1978), John Nelson (1978), Tim Bonin (1979), and the late Jack Johnson (1979-81) piloted helicopters; we are indebted to their skill.

Discussions with John Berti, Erik Erikson, Bernard Evans, Ken Fox, Ralph Haugerud, James McDougall, Robert Miller, James Minard, Joseph Vance, Robert Yeats, and Jim Yount have been highly stimulating and useful. Erik Erikson supplied mineral separates for potassium-argon (K-Ar) radiometric dating of rocks from the Snoqualmie batholith.

Generalized geologic map of the Skykomish River Quadrangle.
Click here for enlarged version with explanation (60K).

Thumbnail of generalized geologic map of the Skykomish River quadrangle
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