Clastic rocks and andesite flows

Mostly andesitic lava flows, domes, breccia, and small intrusive masses and lesser basaltic to rhyolitic rocks; interlayered saprolite, bedded volcaniclastic and epiclastic mudstone, claystone, siltstone, sandstone, conglomerate, and mudflow (lahar) deposits. Mostly consists of Clarno Formation of central Oregon and unnamed rocks of Basin and Range Province in south-central Oregon. Fossil plants and vertebrates in these rocks are Eocene in age. Andesite and basalt lava flows are typically slightly altered; most glass is devitrified and altered to clay minerals, zeolites, and secondary feldspar. Reliable K-Ar ages of rocks from unit range from about 54 Ma to about 37 Ma (Evernden and James, 1964; Fiebelkorn and others, 1983). A number of K-Ar ages on rocks shown on source maps as part of the Clarno Formation are in the range of about 36 to 19 Ma (Fiebelkorn and others, 1983). Although these rocks are lithologically similar to, but generally less altered than, rocks of the Clarno Formation, they are coeval with the John Day Formation. Most of these enigmatic rocks of Oligocene and early Miocene age are included in unit Tas. At base of unit in Blue Mountains Province, locally includes quartzose and feldspathic sandstone, siltstone, and shale largely of granitic or metamorphic provenance; fossil plants in these sedimentary rocks indicate an early Eocene or Paleocene age
State Oregon
Name Clastic rocks and andesite flows
Geologic age Paleocene to Early Oligocene
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Dome, Stock or pipe)also contains basaltic to rhyolitic rocks, volcaniclastic and epiclastic rocks, including mudstone to conglomerate and mudflow (lahar)
Minor
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)
Sedimentary > Clastic > Mudstone (Bed)
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Mudstone > Claystone (Bed)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)
Comments Unit in Umatilla River Basin (OR292) is interpreted as mostly Paleogene volcanic rocks (Eocene, Oligocene, and early Miocene?) that are mainly porphyritic andesite and dacite flows. Includes domes, volcaniclastic deposits, and shallow intrusions, basalt flows and tuffaceous sedimentary rock. Includes the McKay Creek vitrophyre, flows and tuffaceous sedimentary rocks on Willow and Birch Creeks, porphyritic andesite dikes and sills, and quartz-biotite dacite and rhyolite dikes.
Stratigraphic units Clarno Formation
References

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

Brown, C.E. and Thayer, T.P., 1966, Geologic map of the Canyon City quadrangle, northeastern Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-447, scale 1:250,000.

https://pubs.er.usgs.gov/publication/i447

Fiebelkorn, R.B., Walker, G.W., Macleod, N.S., McKee, E.H., and Smith, J.G., 1983, Index to K-Ar determinations for the State of Oregon: Isochron/West, no. 37, p. 3-60.

Prostka, H.J., 1962, Geology of the Sparta quadrangle, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-1, scale 1:62,500.

Swanson, D.A., 1969a, Reconnaissance geologic map of the east half of the Bend quadrangle, Crook, Wheeler, Jefferson, Wasco, , and Deschutes Counties, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-568, scale 1:250,000.

https://pubs.er.usgs.gov/publication/i568

Brooks, H.C., McIntyre, J.R., and Walker, G.W., 1976, Geology of the Oregon part of the Baker 1o by 2o quadrangle: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-7, scale 1:250,000.

Walker, G.W., 1973, Reconnaissance geologic map of the Pendleton quadrangle, Oregon and Washington: U.S. Geological Survey Miscellaneus Geologic Investigations Map I-727, scale 1:250,000.

https://pubs.er.usgs.gov/publication/i727

Walker, G.W., 1977, Geologic map of Oregon east of the 121st meridian: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-902, scale 1:500,000.

https://pubs.er.usgs.gov/publication/i902

Walker, G.W., Peterson, N.V., and Greene, R.C., 1967, Reconnaissance geologic map of the east half of the Crescent quadrangle, Lake, Deschutes, and Crook Counties, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-493, scale 1:250,000.

https://pubs.er.usgs.gov/publication/i493

Robinson, P.T., 1975, Reconnaissance geologic map of the John Day Formation in the southwestern part of the Blue Mountains and adjacent areas, north-central Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-872, scale 1:125,000.

https://pubs.er.usgs.gov/publication/i872

Evernden, J.F and James, G.T., 1964, Potassium-argon dates and the Tertiary floras of North America: American Journal of Science, v. 262, p. 945-974.

Brooks, H.C., Ferns, M.L., and Mullen, A.D., 1982, Geology and mineral deposits of the Granite quadrangle, Grant County, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-25, scale 1:24,000.

Ferns, M.L., Brooks, H.C., and Avery, D.G., 1983, Geology and gold deposits map of the Greenhorn quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-28, scale 1:24,000.

Brooks, H.C., Ferns, M.L., and Avery, D.G., 1984, Geology and gold deposits of the southwest quarter of the Bates quadrangle, Grant County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-35, scale 1:24,000.

Ferns, M.L., Brooks, H.C., and Wheeler, G.R., 1984, Geology and gold deposits of the Bates quadrangle, Grant County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-31, scale 1:24,000.

Ferns, M.L., Brooks, H.C., and Ducette, J., 1982, Geology and mineral resources map of the Mt. Ireland quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series, GMS-22, scale 1:24,000.

Brooks, H.C., Ferns, M.L., Wheeler, G.R., and Avery, D.G., 1983, Geology and gold deposits map of the northeast quarter of the Bates quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-29, scale 1:24,000

Evans, J.G., 1989, Geologic map of the Desolation Butte quadrangle, Grant and Umatilla Counties, Oregon: U.S. Geological Survey Geologic Quadrangle GQ-1654, scale 1:62,500.

https://pubs.er.usgs.gov/publication/gq1654

Evans, J.G., Geologic map of the Beaverdam Creek quadrangle, Baker County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-2299, scale 1:24,000.

https://pubs.er.usgs.gov/publication/mf2299

Evans, J.G., 1993, Geologic map of the Brannan Gulch quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1744, scale 1:24,000.

https://pubs.er.usgs.gov/publication/gq1744

Evans, J.G., 1993, unpub. mapping, Unity Reservoir quadrangle, Baker County Oregon.

Evans, J.G., 1994, unpub. mapping, Hereford quadrangle, Baker County, Oregon.

Brooks, H.C., Ferns, M.L., Nusbaum, R.L., and Kovich, P.M., 1979, Geologic map of the Rastus Mountain quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-79-7, scale 1:24,000.

Ferns, M.L., Brooks, H.C., and Avery, D.G., 1983, Geology and gold deposits map of the Greenhorn Quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-28, scale 1:24,000.

Reef, J.W., 1983, The Unity Reservoir rhyodacite, tuff-breccia and associated volcanic rocks, Baker County, Oregon: Pullman, Washington State University master's thesis, 128 p.

Ferns, M.L., McConnell, V.S., and Madin, I.P., in prep., Geology of the Umatilla River Basin, Morrow, Umatilla, and Union Counties, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report, 66 p., scale 1:100,000.

Waters, A.C., 1968, Reconnaissance geologic map of the Madras quadrangle, Jeffereson and Wasco Counties, Oregon" U.S. Geological Survey Miscellaneous Geological Investigations Map I-555, scale 1;125,000.

https://pubs.er.usgs.gov/publication/i555

NGMDB product
Counties Baker - Crook - Deschutes - Gilliam - Grant - Jefferson - Lake - Malheur - Morrow - Umatilla - Wasco - Wheeler