Geologic units in Franklin county, Washington

Additional scientific data in this geographic area

Quaternary nonmarine deposits (Pleistocene) at surface, covers 35 % of this area

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

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.

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.

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.

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.

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

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

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.

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.

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.