The Potosi Dolomite, also called the Potosi Formation, is a Cambrian geologic formation found in Missouri, Illinois, and Indiana. It is important for preserving fossils from an early period of animal life and for documenting Cambrian environments in the midcontinent of the United States. Fossils reported from the formation include the monoplacophoran Gayneoconus, including G. echolsi. Together, these remains make the formation a significant source of evidence about ancient life and environmental conditions in this region during the Cambrian period.