Tuffaceous siltstone and sandstone (upper and middle Eocene) (ORTss;0)

Thick- to thin-bedded marine tuffaceous mudstone, siltstone, and sandstone; fine to coarse grained. Contains calcareous concretions and, in places, is carbonaceous and micaceous. Includes the Nestucca Formation, which contains a foraminiferal assemblage assigned to the upper Narizian and lowermost Refugian Stages (Snavely and others, 1969; McKeel, 1980); the Spencer Formation, which contains Narizian Stage foraminifers; the Keasey Formation, which contains upper Narizian and lower Refugian Stage foraminifers (McDougall, 1975, 1980); the Coaledo and Bateman Formations of Baldwin (1974); upper Eocene sandstone of Bela (1981); and the Sager Creek formation (informal name) of Niem and Niem (1985)

State	Oregon
Name	Tuffaceous siltstone and sandstone (upper and middle Eocene)
Geologic age	Middle Eocene to Late Eocene
Original map label	Tss
Primary rock type	mudstone
Secondary rock type	siltstone
Other rock types	sandstone
Lithologic constituents	Major Sedimentary > Clastic > Mudstone (Bed) Minor Sedimentary > Clastic > Sandstone (Bed) Sedimentary > Clastic > Siltstone (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. Snavely, P.D., Jr., McLeod, N.S., and Rau, w.w., 1969, Geology of the Newport area, Oregon: The Ore Bin, v. 31, p. 25-71. McKeel, D.R., 1980, Micropaleontological study of five wells, western Willamette Valley, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report 0-80-1, 21 p. McDougall, K., 1975, The microfauna of the type section of the Keasey Formation of Northwestern Oregon, in Weaver, D.W., Hornaday, G.R., and Tipton, A., eds., Future energy horizons of the Pacific Coast: Society of Economic Paleontologists and Mineralogists, Pacific Section, Long Beach, California, 1975, p. 343-359. Baldwin, E.M., 1974, Eocene stratigraphy of southwestern Oregon: Oregon Department of Geology and Mineral Industries Bulletin 83, 40 p. Bela, J.L., 1981, Geology of the Rickreall, Salem West, Monmouth, and Sidney 7-1/2 ' quadrangles, Marion, Polk, and Linn Counties, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-18, scale 1:24,000. Niem, A.R., and Niem, W.A., 1985, Oil and tgas investigation of the Astoria Basin, Clatsop and northernmost Tillamook Counties, northwest Oregon: Oregon Department of Geology and Mineral Industries Oil and Gas Investigation OGI-14, scale 1:100,000.
Geographic coverage	Benton - Clatsop - Columbia - Coos - Douglas - Lane - Lincoln - Linn - Marion - Polk - Tillamook - Washington - Yamhill