Oligocene volcanic rocks (WAOGv;0)

State	Washington
Name	Oligocene volcanic rocks
Geologic age	Oligocene
Lithologic constituents	Major Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-tuff) Minor Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-tuff) Igneous > Volcanic (Volcaniclastic-volcanic breccia) Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow, Pyroclastic-tuff) Incidental Sedimentary > Clastic > Mudstone > Shale (Bed, Carbonaceous) Sedimentary > Clastic > Sandstone (Tuffaceous) Sedimentary > Clastic > Conglomerate (Bed) Sedimentary > Clastic > Sandstone > Arkose (Bed)
Comments	Mapped 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.
Stratigraphic units	Gerome andesite
References	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. 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.
NGMDB product	NGMDB product page for 30777
Counties	Ferry - Lincoln - Skagit - Snohomish - Stevens

State

Washington

Name

Oligocene volcanic rocks

Geologic age

Oligocene

Lithologic constituents

Major

Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-tuff)

Minor

Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-tuff)

Igneous > Volcanic (Volcaniclastic-volcanic breccia)

Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow, Pyroclastic-tuff)

Incidental

Sedimentary > Clastic > Mudstone > Shale (Bed, Carbonaceous)

Sedimentary > Clastic > Sandstone (Tuffaceous)

Sedimentary > Clastic > Conglomerate (Bed)

Sedimentary > Clastic > Sandstone > Arkose (Bed)

Comments

Mapped 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.

Stratigraphic units

Gerome andesite

References

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.

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.

NGMDB product

NGMDB product page for 30777

Counties

Ferry - Lincoln - Skagit - Snohomish - Stevens