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Oligocene volcanic rocks

Andesite and rhyodacite flows, tuff, and tuffaceous sandstones of northern Lincoln County and southwestern Stevens County.
StateWashington
NameOligocene volcanic rocks
Geologic ageOligocene
Original map labelOLv
CommentsMapped as andesite and dacite by Stoffel and others, 1991; mapped as primarily rhyodacite flows by Becraft and Weis, 1963. Note that Stoffel and others, 1991, report that while the term "Gerome Andesite" was once widely used (first coined in 1920 by Stevens), it has since been abandoned.
Primary rock typerhyodacite
Secondary rock typeandesite
Other rock typessandstone; conglomerate; shale; volcanic breccia (agglomerate)
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)
Minor
Igneous > Volcanic (Volcaniclastic, volcanic breccia)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow)
Igneous > Volcanic > Mafic-volcanic > Andesite (Pyroclastic, tuff)
Incidental
Sedimentary > Clastic > Sandstone > Arkose (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)Carbonaceous
Sedimentary > Clastic > Conglomerate (Bed)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, tuff)
Sedimentary > Clastic > Sandstone (Tuffaceous)
Igneous > Volcanic > Felsic-volcanic > Dacite (Pyroclastic, tuff)
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.
Weaver, C. E., 1920, The Mineral Resources of Stevens County: Washington Geological Society Bulletin No. 20, 350 p.
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.
Waggoner, S. Z., 1990a, Geologic Map of the Coulee Dam 1:100,000 Quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 90-15, scale 1:100,000.
Becraft, G. E. and Weis, P. L., 1963, Geology and Mineral Deposits of the Turtle Lake Quadrangle, Washington: U. S. Geological Survey Bulletin 1131, 73 p., 2 pls.
Geographic coverageFerry - Lincoln - Skagit - Snohomish - Stevens

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