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Miocene-Pliocene volcanic rocks

Dark-gray, fine-grained, dense, porphyritic in part, basalt flows in central and south-central part of State; commonly interbedded with conglomerate, sandstone, and siltstone. Includes small areas of rhyolite north of Cle Elum in Kittitas County, and andesite north of Leavenworth in Chelan County.
State Washington
Name Miocene-Pliocene volcanic rocks
Geologic age Miocene-Pliocene
Comments Sedimentary rocks interbedded with Saddle Mountain basalt (which makes up most of this unit) are of Ellensburg Formation, which is mostly conglomerate and pumicite (see unit WAMPLc) (Mackin, 1961, Schuster and others, 1997). The Saddle Mountain Basalt is Miocene-Pliocene in age; the basaltic to rhyolitoc rock, associated with the Teenaway Basalt in the central Cascades, is Eocene in age (Schuster and others, 1997, Tabor and others, 1982).
Primary rock type basalt
Secondary rock type rhyolite
Other rock types andesite; conglomerate; pumice
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)
Incidental
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)Includes rhyolitic tuff.
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)
Sedimentary > Clastic > Conglomerate
Igneous > Volcanic (Pyroclastic, air fall)Pumicite of Ellensburg Formation; may also be described as pumiceous sandstone and siltstone.
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.
Schuster, J. E., Gulick, C.W., Reidel, S. P., Fecht, K. R., Zurenko, S., 1997, Geologic Map of Washington--Southeast Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-45, scale 1:250,000.
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.
Tabor, R. W., Waitt, R. B., Jr., Frizzell, V. A., Jr., Swanson, D. A., Byerly, G. R., Bentley, R. D., 1982, Geologic Map of the Wanatchee 1:100,000 Quadrangle, Central Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1311, scale 1:100,000.
Grolier, M. J. and Bingham, J. W., 1971, Geologic Map and Sections of Parts of Grant, Adams, and Franklin Counties, Washington: U. S. Geological Survey Miscellaneous Geologic Investigations Map I-589, 6 pls., scale 1:62,500.
Counties Benton - Chelan - Grant - Kittitas - Yakima