Mesozoic volcanic rocks, undivided

Includes latite, andesite and basalt flows, tuff, and agglomerate. Interbedded sedimentary rocks in Orient area of Stevens County.
State Washington
Name Mesozoic volcanic rocks, undivided
Geologic age Jurassic
Lithologic constituents
Igneous > Volcanic > Felsic-volcanic > Latite (Flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Igneous > Volcanic > Felsic-volcanic > Rhyolite
Comments The Rossland volcanics in northern Stevens County are dominated by greenstone, augite porphyry, and greenschist with locally intercalated agglomerate (volcanic breccia) (Stoffel, 1990). Joseph, 1990a, includes siltite and specifies that greenstone is dominantly volcanic breccia with regional greenschist facies metamorphism. In Okanogan County, the unit consists of andesitic tuff and tuff breccia with subordinate rhyolite and dacitic tuff and tuff breccia and andesite and basalt flows. Included is minor beds of conglomerate and tuffaceous sandstone, siltstone, and mudstone (Stoffel and others, 1991). Barksdale, 1975, lists andesiteic breccias, sandstone, siltstone, black shale, and conglomerate. Weaver, 1920, however, describes the Rossland volcanic group as predominantly augite and augite-biotite latite lava flows, tuffs, and breccias with subordinate quartz latite and augite andesite and occasional belts of rhyolite and interbedded sediments.
Stratigraphic units Rossland group (in part); Buck Mountain Formation (in part)

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.

Barksdale, J.D., 1975, Geology of the Methow Valley, Okanogan County, Washington: Washington Division of Geology and Earth Resources Bulletin no. 48, 72 p.

Stoffel, K.L., 1990, Geologic Map of the Republic 1:100,000 Quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 90-10, 62 p, 1 pl.

Joseph, N.L., 1990a, Geologic Map of the Colville 1:100,000 Quadrangle, Washington-Idaho: Washington Division of Geology and Earth Resources Open File Report 90-13, 78 p., 1 pl.

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 - Okanogan - Stevens