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Tertiary volcanic rocks, undivided

Includes andesite, basalt, and rhyolite flows, and associated pyroclastic rocks. In isolated areas across the northern part of the State.
State Washington
Name Tertiary volcanic rocks, undivided
Geologic age Mostly Oligocene-Eocene
Comments Stoffel and others, 1991, report that while the term "Pend Oreille andesite" was once widely used, it has since been abandoned. This unit appears to be primarily andesite, followed closely and possibly matched by dacite; rhyolite occurs only incidentally; no mention of basalt in referenced literature.
Primary rock type andesite
Secondary rock type dacite
Other rock types rhyolite
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow)
Minor
Igneous > Volcanic > Felsic-volcanic > Dacite (Volcaniclastic, volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Andesite (Volcaniclastic, volcanic breccia)
Incidental
Igneous > Volcanic > Mafic-volcanic > Andesite (Dike or sill)
Igneous > Volcanic > Felsic-volcanic > Dacite (Pyroclastic, tuff)
Igneous > Volcanic > Mafic-volcanic > Andesite (Pyroclastic)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, ash-flow)
Map references
Huntting, M. T., Bennett, W. A. G., Livingston, V. E. Jr., Moen, W. S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.
Unit references
Huntting, M. T., Bennett, W. A. G., Livingston, V. E. Jr., Moen, W. S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.
Stoffel, K. L., Joseph, N. L., Waggoner, S. Z., Gulick, C. W., Korosec, M. A., Bunning, B. B., 1991, Geologic Map of Washington--Northeast Quadrant: Washington Division of Geology and Earth Resources Geologic Map, GM-39, scale 1:250,000.
Schroeder, M. C., 1952, Geology of the Bead Lake District, Pend Oreille County, Washington: Washington Division of Mines and Geology Bulletin No. 40, 57 p.
Rinehart, C. D., and Fox, K. F., Jr., 1976, Bedrock Geology of the Conconully Quadrangle, Okanogan County, Washington: U. S. Geological Survey Bulletin 1402, 58 p.
Rinehart, C. D., and Fox, K. F., Jr., 1972, Geology and Mineral Deposits of the Loomis Quadrangle, Okanogan County, Washington: Washington Division of Mines and Geology Bulletin No. 64, 124 p.
Tabor, R. W., Frizzell, V. A., Jr., Booth, D. B., Waitt, R. B., Whetten, J. T., Zartman, R. E., 1993, Geologic Map of the Skykomish River 30- by 60-Minute Quadrangle, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1963, scale 1:100,000.
Joseph, N. L., 1990b, Geologic Map of the Nespelem 1:100,000 Quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 90-16, 47 p., 1 pl.
Counties Chelan - Ferry - King - Kittitas - Okanogan - Pend Oreille - Snohomish - Stevens - Whatcom