[1] The formation consists of three facies representing different depositional environments.

These are piedmont slope and alluvial fan deposits, typically composed of light-brown to light-reddish-brown sandstone and fanglomerate; axial stream deposits, which are composed of light-gray to light-yellowish-brown fine- to medium-grained sand and sandstone with fluvial cross-bedding and cut-and-fill channels; and interbedded basalt flows with a K-Ar age of 4.5 +/-0.1 million years (Ma.

)[1] The formation is interpreted as fanglomerates shed from the flanking uplifts of the Rio Grande Rift and channel and floodplain deposits of the ancestral Rio Grande.

[2] The formation has yielded abundant fossils of Irvingtonian age at Tijeras Arroyo, south of Albuquerque International Airport.

[1] The formation was subsequently mapped into the lower Rio Puerco valley[4] and as far north as the Santo Domingo basin.