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Cowlitz Formation (upper and middle Eocene)

Micaceous, arkosic to basaltic marine sandstone, siltstone, and mudstone. Foraminiferal assemblages are referred to the upper Narizian Stage of Mallory (1959) in Newton and Van Atta (1976)
StateOregon
NameCowlitz Formation (upper and middle Eocene)
Geologic ageMiddle Eocene to Late Eocene
Original map labelTco
Primary rock typesandstone
Secondary rock typesiltstone
Other rock typesclaystone
Lithologic constituents
Major
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Minor
Sedimentary > Clastic > Mudstone (Bed)
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.
Mallory, V.S., 1959, Lower Tertiary biostratigraphy of the California Coast Ranges: Tulsa, Oklahoma, American Association of Petroleum Geologists, 416 p.
Newton, V.C. and Van Atta, R.O., 1976, Prospects for natural gas production and underground storage of pipe-line gas in the upper Nehalem River Basin, Columbia-Clatsop Counties, Oregon: Oregon Department of Geology and Mineral Industries Oil and Gas Investigations 5, 56 p.
Geographic coverageClatsop - Columbia - Tillamook - Washington

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