Structure and igneous rocks of the Ruidoso region, New Mexico
— Samuel L. Moore, Tommy B. Thompson, and Eugene E. Foord

Proterozoic igneous rocks (1200 Ma) at Pajarito Mountain are an erosional window of Precambrian basement rocks surrounded by Permian marine rocks. The igneous rocks are hosts to economic zirconium and rare-earth elements. Emplacement of Tertiary igneous rocks began with intrusion of the Black Mountain stock and dike swarm about 39 Ma. The Ruidoso region was then subjected to a period of erosion of about 0.5 Ma before the eruption of the Sierra Blanca volcanic pile. The volcanic pile shows progressive upward enrichment of silica and alkalis. The volcanics in the southern part of the pile range in composition from phonolite through trachyphonolite, trachyandesite, phonotephrite, to trachybasalt, whereas the central and northern parts of the pile range from andesite, latite, to trachyte. The eruption of the volcanic pile and the feeder plugs started about 38 Ma and continued to about 26 Ma. Whole-rock chemistry indicates a single magma source for the Sierra Blanca igneous complex. The Black Mountain stock and dike swarm and the Sierra Blanca volcano and its feeder plugs are intruded along a northeast-trending fault zone that is probably reactivated faults in the Precambrian basement rocks.