The contact between the St. Charles and Garden City Formatlons in the Bear River Range, Bannock thrust sheet in northern Utah and southeastern Idaho, is a diachronous dlsconformity within the Lower Ordovician, Middle or, possibly, upper Cordylodus proavus Zone (Clavohamulus elongatus to, possibly, C. hintzel Subzones) conodonts indicate that lowermost Canadian Series (Lower Ordovician in North American usage) strata equivalent to the Missisquoia Zone and, possibly, lower Symphysurina Zone (trilobites) are present in the upper part of the St . Charles Formation.
United States Geological Survey, "Conodont Biostratigraphy and Thermal Color Alteration Indices of the Upper St. Charles and Lower Garden City Formations, Bear River Range, Northern Utah and Southeastern Idaho" (1981). All U.S. Government Documents (Utah Regional Depository). Paper 26.