[2] The formation is volcanic, consisting mostly of flows of amphibole latites to pyroxene andesites[2] and associated volcaniclastics and tuffs.

The appearance is highly variable, from pinkish gray to red to brown to black, with large to small phenocrysts and with glassy to fully crystalline texture.

Oxygen isotope ratios suggest that the magma from which the formation solidified had its origin in the Earth's mantle and underwent a degree of fractional crystallization.

However, the overlying Sugarlump Tuff has been radiometrically dated as 35.17±0.12 million years old, so the Rubio Peak Formation cannot be younger than this nor older than the Tertiary rocks on which it was deposited.

Bachman (1961) mapped the formation throughout southwestern New Mexico and extended the definition to include some flows that appeared to be of Cretaceous age,[9] but subsequent work has restricted the definition to flows near the type area and of Eocene to Olicocene age.