Named as a member in lower part of Sepulcher Formation of Washburn Group of Absaroka Volcanic Supergroup in Bighorn Peak, MT in the Montana folded belt province, and at Sepulcher Mountain, Yellowstone National Park, WY, Yellowstone province. The type area is the headwaters of Daly Creek in the northwest corner of the Park. Consists of hornblende andesite, pyroxene andesite volcaniclastic rocks of vent and alluvial facies. Includes more than 800 ft of vent facies rocks near mouth of Specimen Creek and grades northwest to about 400 ft of fine-grained alluvial facies. Has spectacular exposures of fossil forests in upper part. Rests on Lost Creek Member of Sepulcher which is dated as 49.2 +/-1.5 m.y. Is overlain by Fortress Mountain Member which has plant fossils of early middle Eocene age.

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