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Mineral Resources > Online Spatial Data > Geology > by state > Washington Geology

Geologic units in Franklin county, Washington

[Additional scientific data in this geographic area]

Eolian deposits (Holocene) at surface, covers 0.5 % of this area

Active dune sand; includes beach sand along southwestern Washington coast.

Lithology: beach sand; dune sand; mud flat

Glaciolacustrine deposits (Pleistocene) at surface, covers < 0.1 % of this area

Fine-grained sand and silt, well-stratified, with some gravel, clay, and diatomaceous earth. Contains clastic dikes in Walla Walla area.

Lithology: glaciolacustrine; alluvium; volcanic ash

Quaternary nonmarine deposits (Pleistocene) at surface, covers 17 % of this area

Periglacial lacustrine deposits. Light-brown, well-sorted and bedded clayey sandstone and sandy clay with interbeds of volcanic ash and calcareous cemented gravels.

Lithology: lake or marine deposit (non-glacial); conglomerate; volcanic ash

Alluvium (Holocene) at surface, covers 2 % of this area

Mostly unconsolidated silt, sand, and gravel valley fill with some clay; includes low-level terrace, marsh, peat, artificial fill, and glacial deposits locally.

Lithology: alluvium; alluvial terrace; peat; glacial drift

Miocene volcanic rocks (Middle Miocene) at surface, covers 20 % of this area

Dark-gray to black, dense aphanitic basalt flows; commonly columnar jointed, less commonly irregularly and platy jointed; some flows vesicular, grading to scoriaceous; includes minor pillow lava, palagonite beds, and interbedded soil profiles and sedimentary beds; contains diatomite beds locally. Maximum thickness in south-central Washington may be in excess of 10,000 feet; much thinner in western Washington, where flows are mostly associated with marine sedimentary rocks. Includes acidic and intermediate volcanic rocks in northern Cascade Mountains.

Lithology: tholeiite; andesite; dacite; rhyolite; sandstone; siltstone; conglomerate

Pliocene-Pleistocene volcanic rocks (Mostly Pleistocene) at surface, covers 0.2 % of this area

Light-gray andesite, andesite porphyry, and open-textured basalt flows with minor associated mudflows and breccia. Includes restricted areas of valley flow basalt in Snake River Canyon in southeastern Washington and in Spokane area.

Lithology: andesite; basalt

Landslide and mudflow deposits (Holocene) at surface, covers 0.2 % of this area

Predominantly landslide debris. Includes till-like mudflow deposits of andesitic rock fragments in clayey sand matrix in Buckley-Enumclaw area of Kind and Pierce Counties.

Lithology: landslide; lahar

Quaternary nonmarine deposits (Pleistocene) at surface, covers 34 % of this area

Periglacial eolian deposits. Buff to light-brown, massive, homogenous, unconsolidated loessial silt; some water-laid material locally. Probably early Pleistocene.

Lithology: loess; glaciolacustrine

Younger glacial drift (Pleistocene) at surface, covers 25 % of this area

Advance and recessional outwash, stratified drift, and associated deposits. Primarily silt, sand, and gravel with some clay. Includes alluvium locally and scabland deposits of eastern Washington.

Lithology: outwash; stratified drift; alluvium