southern Idaho and northern Utah - see also the Garden City Formation
Swan Peak Formation (Zone M):
Eleutherocentrus petersoni Clark (Swan Peak Fm.)
"Symphysurus?" goldfussi Walcott, 1884
Ross, R. J. Jr. (1951) Stratigraphy of the Garden City Formation in northeastern Utah, and its trilobite faunas. Peabody Museum of Natural History, Yale University, Bulletin 6, 161 pp., 36 pls.