Basaltic and andesitic rocks

Lava flows and flow breccia of hypersthene and olivine andesite, basaltic andesite containing plagioclase and pyroxene phenocrysts, and basalt; many flows contain phenocrysts of both hypersthene and augite. Includes interbedded volcaniclastic and epiclastic rocks mostly of andesitic composition, but partly of dacitic or rhyodacitic composition. Includes really restricted flows of silicic andesite or dacite. Upper part of unit mostly unaltered, although olivine crystals are locally altered to clay minerals. Lower parts commonly altered; secondary minerals include nontronite and saponite, chalcedony, calcite, and zeolites. Older parts of this unit locally are propylitically altered adjacent to larger intrusions. Erupted mostly from widespread, northwest- and north-trending dikes and dike swarms and related plugs and lava cones. Potassium-argon ages range from about 10 Ma to about 17 Ma. Much of this unit was previously assigned to the Sardine Formation (Peck and others, 1964), although the type locality of the Sardine Formation ("Sardine Series" as mapped by Thayer, 1939) may be older. Includes Elk Lake Formation (White, 1980a, 1980b), part of the Rhododendron Formation (Trimble, 1963; Wise, 1969), and andesite of Nohorn Creek of Hammond and others (1982)
State Oregon
Name Basaltic and andesitic rocks
Geologic age Middle to Late Miocene
Lithologic constituents
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Volcaniclastic)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Volcaniclastic)

Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.

Peck, D.L., Griggs, A.B., Schlicker, H.G., Well, F.G., and Dole, H.M., 1964, Geology of the central and northern parts of the Western Cascade Range in Oregon: U.S. Geolotgical Survey Professional Paper 449, 56 p.

Thayer, T.P., 1939, Geology of the Salem Hills and the North Santiam River basin, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 15, 40 p.

White, C.M., 1980a, Geology of the Bretienbush Hot Springs Quadrangle, Oregon: Oregon Department of Geology and Mineral Industries Special Paper 9, 26 p.

White, C.M., 1980a, Geology and geochemistry of volcanic rocks in the Detroit area, western Cascade Range, Oregon: Eugene, Oregon, University of Oregon, Ph.D. dissertation, 178 p.

Trimble, D.E., 1963, geology of Portland, Oregon, and adjacent areas: U.S. Geological Survey Bulletin 1119, 110 p.

Wise, W.S., 1969, Geology and petrology of the Mount Hood area-a study of High Cascade volcanism: Geological Society of America Bulletin, v. 80, p. 969-1006.

Hammond, P.E., Geyer, K.M., and Anderson, J.L., 1982, Preliminary geologic map and cross sections of the upper Clackamas and North Santiam Rivers area, northern Oregon Cascade Range: Portland State University Department of Earth Sciences, Portland, Oregon, scale 1:62,500.

NGMDB product
Counties Clackamas - Deschutes - Douglas - Hood River - Jackson - Lane - Linn - Marion - Multnomah