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Precambrian rocks, undivided (WApCA;0)

Geologic Formation in WA, ID

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Lithology

Argillite

Siltstone

Phyllite

Other (6,804 mi²)

Geologic Age

Mesoproterozoic – Early Cambrian (1600 Ma – 521 Ma ago)

Geologic Unit Label

PCA

Predominantly phyllite with some schist, limestone, dolomite, quartzite, and volcanic rocks; northeastern Pend Oreille County. Mainly quartzite sandstone in upper part, dark-gray argillite with sandstone and limestone in middle part, and sandstone with argillite in lower part; southeastern Pend Oreille County. Banded slate with quartzite and dolomite; southwestern Stevens County. Quartzite, siliceous argillite, and argilliceous quartzite grading into argillite and quartz-mica schists form south ot north; southeastern Stevens County. Quartzite, argillite, quartz-feldspar gneiss, and other metamorphic rocks in northeastern Whitman and southeastern Spokane Counties are partly if not all extenstions of the Belt strata.

— USGS