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Sedimentary rocks (Jurassic)

Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In northeast Oregon, includes Graylock Formation, Mowich Group, and Shaw Member (of Snowshoe Formation) of Dickinson and Vigrass (1965); Keller Creek Shale of Brown and Thayer (1966); Weberg, Warm Springs, Snowshoe, Trowbridge, and Lonesome Formations of Lupher (1941); the Coon Hollow Formation of Morrison (1964); and unnamed Jurassic rocks near Juniper Mountain in northern Malheur County (Wagner and others, 1963)
State Oregon
Name Sedimentary rocks (Jurassic)
Geologic age Jurassic
Primary rock type shale
Secondary rock type siltstone
Other rock types graywacke
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Minor
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone > Graywacke (Bed)
Igneous > Volcanic > Mafic-volcanic > Andesite (Pyroclastic, tuff)
Igneous > Volcanic > Felsic-volcanic > Dacite (Pyroclastic, tuff)
Sedimentary > Carbonate > Limestone (Bed)
Metamorphic > Metasedimentary (Greenschist)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)Also breccia and agglomerate
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)Also breccia and agglomerate
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Also breccia and agglomerate
Map references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Unit references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Greene, R.C., Walker, G.W., and Corcoran, R.E., 1972, Geologic map of the Burns quadrangle, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-680, scale 1:250,000.
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.
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
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.
Morrison, R.F., 1964, Upper Jurassic mudstone unit named in Snake River Canyon, Oregon-Idaho boundary: Northwest Science, v. 38, no. 3, p. 83-87.
Wagner, , N.S., Brooks, H.C., and Imlay, R.W., 1963, Marine Jurassic exposures in Juniper Mountain area of eastern Oregon:American Association of Petroleum Geologists Bulletin, v. 47, no. 4, p. 687-691.
Evans, J.G., Geologic map of the Dooley Mountain quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1694, scale 1: 24,000.
Brooks, H.C. and Ferns, M.L., 1979, Geologic map of the Bullrun Rock quadrangle, Baker and Grant Counties, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-79-6, scale 1:24,000.
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.
Counties Baker - Crook - Grant - Harney - Malheur - Wallowa