Pleistocene-Recent volcanic rocks

Predominantly dark-gray to black vesicular basalt; olivine-rich in part. Includes andesite flows and pyroclastic rocks of Mount Baker, Glacier Peak, Mount Rainier, Mount Adams, Mount St. Helens, and all cinder cones in southern part of the State. Also includes some Recent flows southeast of Mount St. Helens.
State Washington
Name Pleistocene-Recent volcanic rocks
Geologic age Pleistocene to Holocene
Lithologic constituents
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Volcaniclastic)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-ash flow, Volcaniclastic)
Comments In general, the oldest flows are primarily basalitic (most prevalent in the large flows adjacent to Mt. Adams) and the younger flows and breccias of all of the peaks are predominantly andesite and dacite. Does not include lahars associated with Mt. Rainier (see WAQs). "Columbia lavas" and "Midway volcanic group" included in stratigraphic units of source map (Huntting and others, 1961), though unmentioned in recent literature.

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.

Walsh, T.J., Korosec, M.A., Phillips, W.M., Logan, R.T., Schasse, H.W., 1987, Geologic Map of Washington-Southwest Quadrant: Washington Division of Geology and Earth Resources, Geologic Map GM-34, scale 1:250,000.

Luedke, R.G., Smith, R.L., Russell-Robinson, S.L., 1983, Map showing distribution, composition, and age of late Cenozoic volcanoes and volcanic rocks of the Cascade Range and vicinity, northwestern United States: U. S. Geological Survey Miscellaneous Investigations Series Map I-1507, scale 1:500,000.

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Counties Clark - Cowlitz - Klickitat - Lewis - Okanogan - Pierce - Skamania - Snohomish - Whatcom - Yakima