Assigned to Portage Lake lava series (new) that contains interbedded lava flows and conglomerate or sandstone beds, including Calumet and Hecla conglomerate. Most conglomerate beds can be recognized for tens of miles northeast and southwest of quad. Where a conglomerate bed tapers out and is missing over a wide or narrow gap along strike of the series, its horizon can be recognized by sequence of lava flows above and below preceding and succeeding conglomerates, and by typical occurrence of detrital material in underlying amygdaloid. Tops of conglomerate beds form excellent reference horizons for stratigraphic subdivision of series; most beds have, in this manner, acquired formal names. They include (ascending) St. Louis conglomerate, Old Colony and Wolverine sandstones, and Kingston, Calumet and Hecla, Houghton, Allouez, Pewabic West, and Hancock conglomerates. Allouez, Houghton, and Calumet and Hecla are shown on map of underground workings between Calumet and Ahmeek. Age is Precambrian (middle Keweenawan).

Source: GNU records (USGS DDS-6; Reston GNULEX).