Miocene-Pliocene marine rocks

Brown-gray, coarse-grained, moderately consolidated, commonly cross-bedded sandstone. Grades locally into gritstone and conglomerate lenses; includes minor shale beds; sandstone often shaly and in some areas grades into claystone.
State Washington
Name Miocene-Pliocene marine rocks
Geologic age Miocene-Pliocene
Lithologic constituents
Major
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone (Bed, Tuffaceous)Mostly lithofeldspathic and feldspatholithic but locally tuffaceous or feldspathic.
Minor
Sedimentary > Clastic > Conglomerate (Bed)
Incidental
Sedimentary > Clastic > Mudstone (Bed)
Comments Montesano Formation overlies Astoria Formation and not always differentiated from it in the literature. Most of the Montesano Formation, however, maps within this unit, and most of the Astoria in the WAM unit (based primarily on Logan, 1987a,b, and Walsh and others, 1987).
Stratigraphic units Montesano Formation; Astoria Formation (in part)
References

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.

Rau, W.W., 1967, Geology of the Wynoochee Valley Quadrangle, Grays Harbor County, Washington: Washington Division of Mines and Geology Bulletin no. 56, 51 p.

Logan, R.L., 1987a, Geologic Map of the South Half of the Shelton and South Half of the Copalis Beach Quadrangles, Washington: Washington Division of Geology and Earth Resources Open File Report 87-9, 16 p., 1 pl.

Logan, R.L., 1987b, Geologic Map of the Chehalis River and Westport Quadrangles, Washington: Washington Division of Geology and Earth Resources Open File Report 87-8, 18 p., 1 pl.

NGMDB product
Counties Grays Harbor - Mason