Wild Horse Mesa
Wild Horse Mesa is the broad volcanic tableland itself, not just the source name attached to nearby Hole-in-the-Wall. The mesa is part of a large Miocene volcanic plateau formed by ash-flow deposits from eruptions in the Woods Mountains area about 17.7 to 17.8 million years ago. The rock sequence named for it, the Wild Horse Mesa Tuff, reaches a reported maximum thickness of about 320 meters at Wild Horse Mesa, making the mesa one of the key places for understanding this volcanic episode.
What the visitor sees is a quiet, elevated desert surface with hard volcanic rock, open sky, sparse vegetation, and long views across the central Mojave National Preserve. Its calm appearance hides a violent origin: hot ash and broken volcanic material once spread across the land, later hardening into the resistant layers that helped preserve the mesa form. The surrounding washes, slopes, and cliffs show where erosion has cut into that old volcanic surface.
About 17.8 million years ago, a powerful eruption blasted outward from a volcanic center in the Woods Mountains in the Eastern Mojave. Propelled by the force of rapidly rising and expanding superheated gases, a ground-hugging cloud of ash and rock fragments spread out at near-supersonic speed across the countryside. Hot, suffocating ash buried shallow lakes and stands of trees. The remains of birds, mammals, and plants are preserved as fossils in the sediments below the ash layer. The May 18, 1980 lateral blast from Mount St. Helens was somewhat analogous. The deposits from three closely spaced, violent eruptions comprise the rock unit called the Wild Horse Mesa Tuff which forms the cliffs of Hole-in-the-Wall.