Tertiary alkali intrusive rocks

Syenite sills in Phalen Lake area, northwestern Stevens County. Porphyritic syenite in Danville area of Northern Ferry County.
State Washington
Name Tertiary alkali intrusive rocks
Geologic age Probably Eocene
Lithologic constituents
Igneous > Plutonic > Syenitic > Syenite (Dike or sill)
Comments Syenite sills in Stevens County more precisely defined as leucocratic shonkinite (Yates and Engels, 1968); porphyritic syenite of Danville area (often referred to as Alkalic rocks of Shasket Creek) more precisely defined as hornblende syenite, pyroxene or nephaline syenite, shonkinite, and monzonite (Stoffel, 1990, Parker and Calkins, 1964). Small polygon in northern Ferry County tagged as WAEv1b in digital coverage is really WATas in original map.

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.

Parker, R.L. and Calkins, J.A., 1964, Geology of the Curlew Quadrangle Ferry County Washington, U.S. Geological Survey Bulletin 1169, 95 p.


Yates, R.G. and Engels, J.C., 1968, Potassium-Argon Ages of Some Igneous Rocks in Northern Stevens County, Washingon: U. S. Geological Survey Professional Paper 600-D, p. D242-D247.

Stoffel, K.L., 1990, Geologic Map of the Republic 1:100,000 Quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 90-10, 62 p, 1 pl.

NGMDB product
Counties Ferry - Stevens