Two fundamentally different types of proterozoic rock sequences are juxtaposed in the north central Tusas Mountains.

The assemblage to the north includes mafic metavolcanic, immature metasedimentary rocks of the Moppin complex, and intermediate metaplutonic rocks of the Maquinita Granodiorite. These rocks are some of the oldest in northern New Mexico, and are interpreted to have developed in an island arc setting.

The sequence to the south is a diverse array of supracrustal felsic metavolcanic, felsic metaplutonic, and immature to supermature metasedimentary rocks of the Vadito Group, and Ortega Quartzite. Metaplutonic rocks of the Tres Piedras and Tusas Granites are interpreted to have intruded shortly after the Ortega Quartzite deposition.