The presence of volcanic ash beds in the formation, which can be radiometrically dated, gives the absolute age of the fossils, which is valuable for establishing the geologic time scale of the Neogene.

[4] However, more recent work has yielded an age range of 12 to 13 Ma for a Lower Coarse White Ash Zone towards the base of the formation, which is thickest northeast of the Jemez Mountains and has been interpreted as ash fall from early silicic volcanic activity from vents now buried under later flows.

In other words, the lower part of the formation contains sediments eroded from the Ojo Caliente Member, rather than recording a fluctuating depositional environment.

The artiodactyl Osbornoceros osborni was first located in the formation in the Lyden area,[8] as was the only known specimen of the taxideine badger, Chamitataxus.

[9] The beds making up the unit were originally included by Bryan and McCann in 1937 in the Middle Red member of the Santa Fe Formation.