Age of the Kingsbury conglomerate is Eocene 

The Kingsbury conglomerate and immediately overlying gravels on the east side of the Bighorn Mountains in Wyoming interfinger eastward with “Wasatch” strata. The latter contain Eocene vertebrates, species of which have been found in the Kingsbury conglomerate. In addition, the “Wasatch” strata contain an Eocene flora that includes the floating fern, Salvinia preauriculata Berry, which, because it is not found in earlier beds, permits recognition of the Paleocene-Eocene boundary in the Rocky Mountains and Plains region.