Skip to main content

Cretaceous sedimentary rocks, mostly marine

Upper Cretaceous black siltstone, graywacke, and silica pebble conglomerate in western Okanogan County.
State Washington
Name Cretaceous sedimentary rocks, mostly marine
Geologic age Cretaceous
Comments Huntting and others, 1961, originally places Virginian Ridge Formation in WAKl, referencing a 1958 unpublished map by Barksdale but more recent mapping by Barksdale (1975) shows that most of the Virginian Ridge Formation is actually in this unit. Virginian Ridge Formation is 1080-11,600 ft. thick and Winthrop Sandstone is 0-13,500 ft thick (Barksdale, 1975).
Primary rock type arkose
Secondary rock type siltstone
Other rock types shale; graywacke; conglomerate
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone > Arkose (Bed)
Minor
Sedimentary > Clastic > Siltstone (Bed)
Incidental
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Sandstone > Graywacke (Bed)
Map references
Huntting, M. T., Bennett, W. A. G., Livingston, V. E. Jr., Moen, W. S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.
Unit references
Huntting, M. T., Bennett, W. A. G., Livingston, V. E. Jr., Moen, W. S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.
Barksdale, J. D., 1975, Geology of the Methow Valley, Okanogan County, Washington: Washington Division of Geology and Earth Resources Bulletin no. 48, 72 p.
Counties Okanogan - Whatcom