The field relations and megascopic character of three types of stromatolites, and the bioherms, occurring in the lower half of what is herein defined as the Nash Formation, are described and illustrated. The Nash Formation is part of a succession of metasediments occurring in the Precambrian complex of the Medicine Bow Mts. It is believed to be not less than 1.7 b.y. old. Field studies support the conclusion that the stromatolites and bioherms are organo-sedimentary features.