Named as a formation, one of five formations, of Phantom Lake Metamorphic Suite in the northern Medicine Bow Mountains, for old townsite of Colberg, Carbon Co, WY in the Northern Rocky Mountain region. Type locality is east of Colberg, sec 10, T18N, R79W. Is a heterogeneous assemblage of metavolcanic rocks, including amygdaloidal metabasalts, and a few poorly preserved pillow basalts, volcaniclastic schists, fragmental metavolcanic rocks ranging in composition from rhyolitic to basaltic, paraconglomerates, and thin quartzites. Geologic map. Stratigraphic charts. Petrographic data. Paraconglomerates are very distinctive and they are present in varying proportions of rounded granite boulders (as large as 50 cm in diameter), quartzite boulders and stretched mafic volcanic rocks clasts in an amphibolite, biotite, quartz matrix. Paraconglomerates are up to 400 m thick. Formation ranges from a feather edge in northwest part of mountains to 2,500 m thick in north-central part of mountains. Contacts with overlying Conical Peak Quartzite (named) of Phantom Lake and underlying Bow Quartzite (named) of Phantom Lake are conformable. Depositional history not well known. Partly marine origin; probably deposited in alluvial or submarine channels. Of Late Archean age.

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