This study reports on the continuing work delineating the distribution of diatoms, pollen and spores recovered from the aquicludes within Hagerman Fossil Beds National Monument in the Snake River Buttes near Hagerman, Idaho. Hagerman Fossil Beds National Monument is best known for the Hagerman horse, Equus simplicidens, a late Pliocene (3.5 million years ago) zebra-like species, extensively quarried from the locality since the 1930s. An inquiry was made into the microflora of the aquicludes 200 feet stratigraphically below the deposits that contain the horse quarry (approximately 3100 feet elevation). Five sections containing twenty carbonaceous paper shale samples were taken from the aquiclude. The diatom flora as well as the pollen and spore content of the sediments is interesting because it sheds some light on the character of the local flora at the time contemporary with the Hagerman Horse (Equus simplicidens). The sediments of the aquicludes are not the sediments within which the vertebrates were entombed. Forms present indicate oligotrophic fresh water, with water lilies and accompanying epiphytic algae. The epiphytic diatoms indicate the presence of cold clear water associated with primary order streams and ponds. Grass pollen associated with local grasslands and probable regional wind transport of bisaccates indicate the presence of nearby coniferous stands. The overall impression is that the primary community associated with the formation of the aquicludes was an upland wet meadow surrounding biogenically (beaver) or geologically (lava flows) created oligotrophic ponds.

Key words: 3.5 MYBP, aquicludes, diatoms, Equus simplicidens, late Pliocene, pollen and spores