Geologic units in Jefferson county, Washington

Additional scientific data in this geographic area

Mesozoic-Tertiary marine rocks, undivided (Miocene to Eocene) at surface, covers 54 % of this area

Dark-gray, massive to poorly bedded gray-wacke of the interior Olympic Peninsula; commonly with interbedded slate, argillite, volcanic rocks, and minor arkosic sandstone. Includes rocks both older and younger than Ev2, some of which may be Paleozoic.

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

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.

Middle and lower Eocene volcanic rocks (Eocene) at surface, covers 15 % of this area

Dark-gray, course- to fine-grained, strongly chloritized basalt flows and breccia; includes pillow lava, deeply altered palagonite beds, amygdoidal and vesicular flows, and, locally, sedimentary rocks. Comprises outer volcanic belt in Olympic Peninsula, where manganese ore is associated with some submarine lavas.

Younger glacial drift (Pleistocene) at surface, covers 5 % of this area

Younger glacial drift, undivided. Till, outwash, and associated deposits; sorted and unsorted sand, gravel, silt, and clay. Includes some alluvium.

Pre-upper Eocene rocks (Eocene (Olympic Peninsula); Cretaceous(?) (Yakima County)) at surface, covers 3 % of this area

Argillite and graywacke between inner and outer volcanic belts in Olympic Peninsula. Sheared carbonaceous argillite, argillite, graywacke, and minor conglomerate lenses and altered lava flows in western Yakima County.

Oligocene marine rocks (Late Eocene to Late Oligocene) at surface, covers 3 % of this area

Massive, tuffaceous and nontuffaceous sandstone and siltstone; locally concretionary; includes conglomerate along the north coast of Olympic Peninsula and basaltic sandstone east of Chehalis.

Glacial drift, undivided (Pleistocene) at surface, covers 1 % of this area

Glacial and glaciofluvial sand, gravel, and till; includes alpine glacier outwash and till as well as some Recent alluvium.

Upper upper Eocene nonmarine and marine rocks (Middle Eocene) at surface, covers 1 % of this area

Massive to thin-bedded, feldspathic to arkosic sandstone, siltstone, shale, and carbonaceous shale; becomes mostly marine in the western foothills of Cascade Mountains where coal beds are abundant. Basaltic sandstone and siltstone in northern Olympic Peninsula.

Mesozoic-Tertiary volcanic rocks, undivided (Oligocene to Eocene) at surface, covers 0.7 % of this area

Altered basalt, pillow lavas, and flow breccia of inner volcanic belt of Olympic Peninsula; includes minor interbedded red limy argillite and associated manganese ore.

Alluvium (Holocene) at surface, covers 0.5 % 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.

Oligocene-Miocene marine rocks (Oligocene) at surface, covers < 0.1 % of this area

Massive to thin-bedded, coarse-grained sandstone, conglomerate, conglomeratic sandstone, shale, and sandy shale.

Miocene marine rocks (Miocene) at surface, covers < 0.1 % of this area

Massive to thin-bedded, friable, basaltic to feldspathic sandstone, with shale, siltstone, and local pebble conglomerate interbeds.