Named for sequence of felsic and mafic volcanic rock and intercalated rock that crops out on Cornwallis Peninsula and on few of adjacent Keku Islets. Type locality designated as shore line 3 to 3.5 mi east of Cornwallis Point, Kuiu Island, southeastern AK. Lenticular unit is dominantly altered felsic flow rock and flow breccia. Maximum thickness is probably over 1000 ft; thins abruptly to north and east, is absent in northeastern Keku Islets. Interpreted to unconformably overlie Pybus Formation. Contact not exposed but scattered poor outcrops on forest-covered southwest slope of Cornwallis Peninsula suggest that there may be an extensive chert and limestone-clast conglomerate at base of unit. Conformably underlies Cornwallis Limestone (new). Shown on geologic map of Keku Islets and neighboring parts of Kuiu and Kupreanof Islands. Age is Late Triassic (Karnian) based on fossil collections identified by N.J. Silberling, written commun., 1963).

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