Geologic framework of Tertiary intrusions of the Cornudas Mountains, southern New Mexico
— Constance J. Nutt and J. Michael O'Neill

The Cornudas Mountains in southern New Mexico are underlain by Eocene to Oligocene syenite and phonolite that intrude the Permian Hueco Formation, an anomalously thin Yeso Formation, the San Andres Formation and the Lower Cretaceous Cox, Campagrande, Mesilla Valley, and Muleros Formations. The alkaline intrusions rose along pre-Permian faults near and at the edge of the Pedernal uplift, and moved laterally along the unconformity between Precambrian rocks and the base of the Permian and along the disconformity between the Permian San Andres and overlying Cretaceous rocks. The present-day level of erosion exposes a variety of intrusive forms. Intrusions caused a series of continuous anticlines and synclines and local sags and uplifts in the Permian rocks. Cretaceous rocks occur only in patches along the edges of the resistant intrusions and are remnants of a mostly eroded section that once covered the area. Cretaceous rocks are preserved in and beneath Quaternary landslides that slid off Alamo, San Antonio, Chattfield, and Black Mountains.