The unit was first defined by Stark and Dapples in 1959, during their mapping of the Los Pinos Mountains, as the Sevilleta rhyolite.

[2] Bauer and Pollock called the unit the Sevilleta metarhyolite in their compilation of radiometric ages in 1993.

[3] The unit is a thick sequence of interbedded metarhyolites, pelitic schists, and amphibolites.

The modal composition is 25% quartz, 30% plagioclase, 40% potassium feldspar, 1% muscovite, 1% biotite, 1% epidote, 1% oxides, and 1% accessory minerals.

[5] Similar beds are found in the Hells Canyon area of the northern Manzanita Mountains (34°53′31″N 106°24′11″W / 34.892°N 106.403°W / 34.892; -106.403) and the Monte Largo Hills (35°10′59″N 106°16′41″W / 35.183°N 106.278°W / 35.183; -106.278).