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Stratigraphy of the Red Mountain formation (Lower Pennsylvanian?) of Northwestern Washington Smith, Clyde Louis


The Red Mountain formation (Lower Pennsylvanian?) of the Chilliwack group (Carboniferous) was mapped in five areas of northwestern Washington. Except for a few outcrops of Devonian strata, the formation represents the oldest known sedimentary rocks in this region. It consists primarily of argillite, graywacke, chert, tuff and limestone, and is overlain by conglomerate of the Black Mountain formation (Lower Permian). The base of the formation is nowhere exposed. Correlation of the Red Mountain formation is dependent essentially on the presence of large crinoid stems, foraminifera, and similarity of stratigraphic relationships. Limestones of the upper portion of the formation represent deposition under conditions of marked tectonic stability, whereas enclosing strata are indicative of deposition in an unstable, subsiding realm.

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