Miocene marine rocks

Massive to thin-bedded, friable, basaltic to feldspathic sandstone, with shale, siltstone, and local pebble conglomerate interbeds.
State Washington
Name Miocene marine rocks
Geologic age Miocene
Lithologic constituents
Sedimentary > Clastic > Sandstone (Bed, Tuffaceous)Includes wacke and arenite sandstone and tuffaceous sandstone, relative proportions of each unknown.
Sedimentary > Clastic > Siltstone (Bed, Carbonaceous, Tuffaceous)Includes carbonaceous, micaceous, and tuffaceous siltstone, relative proportions of each unknown.
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Comments Montesano Formation overlies Astoria Formation and not always differentiated from it in the literature. Most of the Montesano Formation, however, maps within the WAMPL unit, and most of the Astoria in this unit (based primarily on Walsh and others, 1987).
Stratigraphic units Astoria Formation; Clallum Formation (Olympic Peninsula); Montesano Formation (in part); Lincoln Creek Formation (in small part)

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Walsh, T.J., Korosec, M.A., Phillips, W.M., Logan, R.T., Schasse, H.W., 1987, Geologic Map of Washington-Southwest Quadrant: Washington Division of Geology and Earth Resources, Geologic Map GM-34, scale 1:250,000.

Babcock, R.S., Suczek, C.A., Engebretson, D.C., 1994, The Cresent "Terrane", Olympic Peninsula and Southern Vancouver Island, in Lasmanis, R. and Cheney, E. S., convenors, Regional Geology of Washington State: Washington Division of Geology and Earth Resources Bulletin 80, p. 141-157.

Wells, R.E., 1989, Geologic Map of the Cape Disappointment-Naselle River Area, Pacific and Wahkiakum Counties, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1832, scale 1:62,500.

Snavely, P.D.,Jr., Brown, R.D., Roberts, A.E., Rau, W.W., 1958, Geology and Coal Resources of the Centralia-Chelalis District, Washington: U. S. Geological Survey Bulletin 1053, 149 p.

Walsh, T.J., 1987, Geologic Map of the Astoria and Ilwaco Quadrangles, Washington and Oregon: Washington Division of Geology and Earth Resources Open File Report 87-2, scale 1:100,000.

NGMDB product
Counties Clallam - Grays Harbor - Jefferson - Lewis - Pacific - Thurston - Wahkiakum