Eocene-Oligocene volcanic rocks

Predominantly light-green, bedded andesite breccia with interbedded andesite and basalt flows, mudflows, and tuff beds; becomes more tuffaceous near top of unit. Includes tuffaceous and arkosic sandstone, shale, and carbonaceous shale beds in central and southern Cascade Mountians. Rhyodacite and quartz latite flows in northwestern Ferry County.
State Washington
Name Eocene-Oligocene volcanic rocks
Geologic age Eocene-Oligocene
Lithologic constituents
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Sedimentary > Clastic > Sandstone > Arkose (Bed)
Igneous > Volcanic > Felsic-volcanic > Quartz-latite (Flow)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)
Comments Percentage of dacite thought to be andesite in the field; predominate over basaltic and rhyolitic rock (Warren, 1941). Large flows in Ferry County mostly dacite and andesite (Stoffel and others, 1991).
Stratigraphic units Enumclaw; Keechelus andesite (lower part); Sanpoil volcanics

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Luedke, Robert G., 1998, Maps showing distribution, composition, and age of Early and Middle Cenozoic volcanic centers in Oregon and Washington: U.S. Geological Survey Miscellaneous Investigations Series Map I-2291-D, scale 1:1,000,000.


Weaver, C.E., 1916, The Tertiary Formations of Western Washington: Washington Geological Survey Bulletin No. 13, 327 p., 3 pls.

Warren, W.C., 1941, Relation of the Yakima Basalt to the Keechelus Andesite Series: The Journal of Geology, v. 49, p. 795-814.

Parker, R.L. and Calkins, J.A., 1964, Geology of the Curlew Quadrangle Ferry County Washington, U.S. Geological Survey Bulletin 1169, 95 p.


Muessig, S., 1967, Geology of the Republic Quadrangle and a Part of the Aeneas Quadrangle, Ferry County, Washington: U. S. Geological Survey Bulletin 1216, 135 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.

NGMDB product
Counties Clark - Cowlitz - Ferry - King - Kittitas - Klickitat - Lewis - Okanogan - Pierce - Skamania - Snohomish - Yakima