Flows and clastic rocks, undifferentiated

Chiefly basaltic andesite and andesite lava flows and flow breccia containing plagioclase and pyroxene (hypersthene and augite) phenocrysts, mudflows (lahars), and volcanic conglomerates; locally includes some dacite flows. Includes lesser, coarse- to fine-grained epiclastic volcanic sedimentary rocks and ash-flow and air-fall tuffs. Partly equivalent in age to unit Tba and may be partly coeval with younger parts of unit Tstb. Locally altered adjacent to larger intrusions. The oldest radiometrically dated rocks assigned to this unit are about 17 Ma (Sutter, 1978); in part lapped by flows questionably assigned to unit Tba, radiometrically dated at about 10 Ma, and unconformably overlain by flows of unit Trb. Includes some of rocks formerly mapped as Sardine Formation and some mapped as Rhododendron Formation
State Oregon
Name Flows and clastic rocks, undifferentiated
Geologic age Miocene
Lithologic constituents
Major
Sedimentary > Clastic > Conglomerate (Bed)
Igneous > Volcanic (Volcaniclastic-lahar)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Volcaniclastic-volcanic breccia)
Incidental
Igneous > Volcanic > Mafic-volcanic (Pyroclastic)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Volcaniclastic-volcanic breccia)
Sedimentary > Clastic > Mixed-clastic (Bed)
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Felsic-volcanic (Pyroclastic-air fall, Pyroclastic-ash flow)
References

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

Sutter, J.F., 1978, K-Ar ages of Cenozoic volcanic rocks from the Oregon Cascades west of 121o 30': Isochron/West, no. 21, p. 15-21.

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