These are older volcanoes and volcanic rocks dating from the Neogene. They represent part of the great ignimbrite flare-up that occurred throughout the Southwest at this time. Many of these eruptions resulted in large calderas similar to the modern Valles Caldera. However, 20 to 35 million years of erosion and faulting have erased most of the morphology of large calderas. Today this area is dominated by massive cliffs of ash flow tuffs and exposures of shallow batholiths consisting of granitic and intermediate volcanic rocks.
Below is a map showing the principal super volcanoes (large calderas) in relation to modern relief in southwestern New Mexico. Note that the Gila Wilderness is probably a wilderness because the underlying geology is so "wild."
Cross section and state of preservation of an idealized Datil-Mogollon supervolcano
-Concept: a Valles Caldera chopped up by Basin and Range like faulting
View Datil-Mogollon Volcanic Field in a larger map