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Flows and clastic rocks, undifferentiated (ORTfc;0)

Geologic Formation in OR

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Lithology

Andesite

Conglomerate

Andesite

Other (3,972 mi²)

Geologic Age

Miocene (23.03 Ma – 5.33 Ma ago)

Geologic Unit Label

Tfc

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

— USGS

Taxonomy

Classified As

Geologic Formation