Terrace deposits

Unconsolidated to partly consolidated fluvial and glaciofluvial sand and gravel with minor amounts of silt and clay. Includes marine terrace along west coast of the Olympic Peninsula.
State Washington
Name Terrace deposits
Geologic age Pleistocene
Lithologic constituents
Unconsolidated > Coarse-detrital > Sand (Glacial, Terrace-marine)
Unconsolidated > Coarse-detrital > Gravel (Glacial, Terrace-marine)
Unconsolidated > Fine-detrital > Silt (Glacial, Terrace-marine)
Unconsolidated > Fine-detrital > Clay (Glacial, Terrace-marine)
Comments Montesano Formation is much older--perhaps "Montesano series" (as listed in Huntting and others, 1961) refers to sediments sourced in this Formation. Terrace deposits are composed of gravel, pebbles, boulders in a sandy matrix; along the Cowlitz River, the deposits are 50 to 70 ft thick and are cemented with limonite derived from ground water (Roberts, 1958). Tabor and Cady, 1978, map most of this unit as morainal and stratified deposits from the continental ice sheet or Olympic alpine glaciers with river terraces which may or may not be related to glaciation. The Hoh Formation has been mapped within this unit (along the western coast of the Olympic Peninsula), presumably where it is exposed underneath the glacial and terrace deposits (Rau, 1979, Dragovich and others, 2002); I have chosen not to include it in this unit description but a small portion of it is included in unit WAMZT--see cited references above for more information. Similarly small pieces of the Quillayute Formation may be exposed within this unit but are not included in the description of this unit--again see Rau, 1979, and Dragovich and others, 2002, for more information.
Stratigraphic units Montesano series

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.

Snavely, P.D., MacLeod, N.S., Niem, A.R., 1993, Geologic map of the Cape Flattery, Challam Bay, Ozette Lake, and Lake Pleasant Quadrangles, Northwestern Olympic Peninsula, Washington: U. S. Geological Survey Map I-1946, scale 1:48,000.

Roberts, A.E., 1958, Geology and Coal Resources of the Toledo-Castle Rock District, Cowlitz and Lewis Counties, Washington: U. S. Geological Survey Bulletin 1062, 71 p, 6 pls.

Dragovich, J.D., Logan, R.L., Schasse, H.W., Walsh, T.J., Lingley, W.S., Jr., Norman, D.K., Gerstel, W.J., Lapen, T.J., Schuster, J.E., Meyers, K.D., 2002, Geologic Map of Washington-Northwest Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-50, scale 1:250,000.

Tabor, R.W. and Cady, W.M., 1978, Geologic Map of the Olympic Peninsula, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-994, scale 1:125,000.

Rau, W.W., 1979, Geologic Map in the Vicinity of the Lower Bogachiel and Hoh River Valleys, and the Washington Coast: Washington Division of Geology and Earth Resources Geologic Map GM-24, scale 1:62,500.

NGMDB product
Counties Chelan - Clallam - Clark - Cowlitz - Grays Harbor - Jefferson - Lewis - Mason - Okanogan - Pacific - Thurston