Ar/Ar data are for 12 samples that record the eruption age of tephra. The geochronology provides time constraints for the ages of tephra and interbedded sediments and fossils from Kenya and Ethiopia. Samples were collected by Erin Dimaggio (Pennsylvania State University), who brought them to the USGS Denver Argon Geochronology Laboratory for Ar/Ar analysis. Samples were analyzed in January 2024.