No type locality designated. Was measured northwestward from bridge on west branch of Nash Fork, which is the outlet for Telephone Lakes, T16N, R78 and 79W, Albany Co, WY in the Northern Rocky Mountain region. Is a thick (2,400 ft) formation that has dolomitic marble and chloritic schist, with some pyroclastic rocks, and some thin beds of jasper and black slate. The marble is white, gray to rose colored. The marbles are banded gray to black and have many concentric domes and globes which may have been built by calcareous algae or other organisms. Was probably originally composed of shale, dolomite, and limestone. Is younger than Sugarloaf metaquartzite (new) and older than Anderson phyllite (new). Assigned to the pre-Cambrian. Is probably early Algonkian.

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

A three-fold unit consisting of Nash Marble (oldest), Anderson Phyllite, and Ranger Marble (youngest) of Blackwelder (1926) is combined into one map unit named the Nash Fork Formation of the Libby Creek Group. Anderson Phyllite is a lenticular unit and cannot be traced beyond the Anderson mining prospect on Libby Creek, Albany Co, WY. Phyllites, which were the only lithology used to separate Nash from Ranger, occur at different stratigraphic levels in the Nash of Blackwelder. Locally, where marble and phyllite can be distinguished on the geologic map of this report, phyllite is shown as separate lithology and as part of the Nash Fork. Blackwelder's Nash, Anderson, and Ranger not used.

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