Carboniferous rocks

Thin-bedded graywacke, shale, argillite, slate, schist, volcanic breccia, gritstone, conglomerate, and limestone on northeast shore of Orcas Island. Limestone or dolomitic limestone, apparently interbedded with limy argillite and graywacke, forms belt of small separate outcrops between Springdale and Valley in southeastern Stevens County. Late Devonian to Early Pennsylvanian in age.
State Washington
Name Carboniferous rocks
Geologic age Late Devonian to Mississippian
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone > Graywacke (Bed)
Minor
Metamorphic > Metasedimentary > Metaclastic > Argillite (Greenschist)
Sedimentary > Carbonate (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Incidental
Metamorphic > Schist (Greenschist)
Sedimentary > Clastic > Conglomerate (Bed)
Igneous > Volcanic (Volcaniclastic-volcanic breccia)
Metamorphic > Metasedimentary > Metaclastic > Slate (Greenschist)
Comments Brandon and others, 1988, maps the outcrop on Orcas Island as the East Sound Group (see also WAD), which is primarily andesitic to dacitic pyroclastic rocks, with rare lava flows, as well as minor limestone; he specifically distinguishes this rock group from the Deadman Bay Terrane which includes chert as well as basalt and limestone. May include incidental Turtleback Complex (see WApPMg and WApTm). The series of outcrops in Stevens County are composed of metalimestone, metadolomite, metaconglomerate, meta-argillite, metasiltstone, and metachert (Stoffel and others, 1991)
Stratigraphic units East Sound Group (in part)
References

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.

Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, C.W., Korosec, M.A., Bunning, B.B., 1991, Geologic Map of Washington--Northeast Quadrant: Washington Division of Geology and Earth Resources Geologic Map, GM-39, scale 1:250,000.

Brandon, M.T., 1989, Geology of the San Juan-Cascade Nappes, northwestern Cascade Range and San Juan Islands, in Joseph, N. L. (Ed.), Geologic Guidebook for Washington and Adjacent Areas: prepared for the 85th Annual Meeting of the Cordilleran Section, Geological Society of America, May 8-11, 1989, Spokane, Washington: Washington Division of Geology and Earth Resource Infomation Circular 86, p. 137-162.

Brandon, M.T., Cowan, D.S., Vance, J.A., 1988, The Late Cretaceous San Juan thrust system, San Juan Islands, Washington: Geological Society of America Special Paper 221, 81 p. 1 pl.

NGMDB product
Counties San Juan - Stevens