Imnaha Basalt

Mostly coarse-grained, plagioclase porphyritic basalt; flows commonly contain zeolite amygdules and montmorillonitic alteration is widespread. Potassium-argon ages mostly 16 to 17 Ma (McKee and others, 1981)
State Oregon
Name Imnaha Basalt
Geologic age Early Miocene
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)
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

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.

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., 1979, Reconnaissance geologic map of the Oregon part of the Grangeville quadrangle, Baker, Union, Umatilla, and Wallowa Counties, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-1116, scale 1;250,000.

https://pubs.er.usgs.gov/publication/i1116

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

Mckee, E.H., Hooper, P.R., and Kleck, W.D., 1981, Ages of Imnaha Basalt--oldest of basalt flows of the Columbia River Basalt Group, northwest United States: Isochron/West, no. 31, p. 31-33.

Brooks, H.C., 1979, Geologic map of the Oregon part of the Mineral quadrangle: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-12, scale 1:62,500.

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

Weiss, P.L., Gualtieri,, J.L., Cannon, W.F., Tucher, E.T., McMahan, A.B., and Federspiel, F.E., 1976, Mineral resources of the Eagle Cap Wilderness and adjacent areas, Oregon: U.S. Geological Survey Bulletin 1385-E, 100 p.

https://pubs.er.usgs.gov/publication/b1385E

NGMDB product
Counties Baker - Grant - Union - Wallowa