Eocene volcanic rocks

Predominantly andesite flows and breccia; includes interbedded sedimentary rocks south of Startup in Snohomish and King Counties.
State Washington
Name Eocene volcanic rocks
Geologic age Eocene
Lithologic constituents
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Volcaniclastic-volcanic breccia, Pyroclastic-tuff)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Volcaniclastic-volcanic breccia, Pyroclastic-tuff)
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone (Bed, Tuffaceous)Feldspathic to volcaniclastic to tuffaceous.
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Volcaniclastic-volcanic breccia, Pyroclastic-tuff)Possibly breccia and tuff as well. Possibly minor in rank.
Sedimentary > Clastic > Conglomerate (Bed)
Metamorphic > Metasedimentary > Metaclastic > Argillite
Comments Luedke, 1998, indicates that some of this unit is basaltic; Tabor and others, 1993, reports that this unit is mostly andesite flows, tuff, porphyry and breccia with minor dacite, dacite breccia, and basalt, and minor volcaniclastic sandstone, conglomerate, and siltstone; Smith, 1993, reports that this unit is all Eocene andesite. Dragovich and others, 2002, reports that this unit is mostly andesite but includes basalt and dacite flow, breccia, and tuff with interbedded sandstone, conglomerate, and argillite.

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.


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.

Smith, J.G., 1993, Geologic Map of Upper Eocene to Holocene Volcanic and Related Rocks in the Cascade Range, Washington; U. S. Geological Survey Miscellaneous Investigations Series Map I-2005, scale 1:500,000.

Dragovich, J.D., Logan, R.L., Schasse, H.W., Walsh, T.J., Lingley, W.S., Jr., Norman, D.K., Gerstel, W.J., Lapen, T.J., Schuster, J.E., Meyers, K.D., 2002, Geologic Map of Washington-Northwest Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-50, scale 1:250,000.

NGMDB product
Counties King - Lewis - Snohomish