The Gila’s Sleeping Giants

If you work your way south and west along the edge of the Colorado Plateau from the Zuni-Bandera Volcanic Field (Highway 117 to Highway 60 by car), it won’t be too long until you find yourself smack-dab in the middle of yet another gigantic swath of jagged, volcano-dominated terrain.

The Gila Wilderness

For geologists, this transition zone between the Colorado Plateau and Basin and Range is known as the Mogollon-Datil Volcanic Field, but your average New Mexican is more likely to refer to it as “The Gila” — shorthand for an area under Forest Service jurisdiction that’s more-or-less coextensive with the aforementioned geologic unit.

Boasting close to 900 square miles of wood and stream and meadow and mountain, The Gila could swallow up a modern explorer for decades. I’ve so far made only one real journey there myself — a 13-mile slosh up the Middle Fork of the Gila River several weekends ago — but that’s all it took for The Gila to jump right to the top of my adventure to-do list.

So much life down there swimming in the waters and clinging to the cliffs; so many nooks and crannies to poke around in. Plus, since The Gila’s remote as all get-out, encounters with other humans are minimal-to-nonexistent.

Supervolcanoes

To be sure, I will write more on recreational offerings at a later date, but let’s focus on the rocks for now. As suggested above, while The Gila bears witness to a wide array of geological processes, it is the aftermath of violent volcanic eruptions that dominates your field of view.

Specifically, geologists hold a quartet of giant supervolcanoes (a.k.a. “calderas”) responsible for building the foundation of this rugged place. Ranging in age from 35 to 20 million years old, these supervolcanoes were the result of a succession of silica-rich magma plumes that bubbled upwards from the Earth’s mantle. In the case of each, the crust warped, creating a steadily-swelling dome structure on the surface.

Eventually, as you might imagine, the pressure became too great and the domes exploded. Ash poured out over the surrounding landscape — sometimes in layers hundreds of feet thick. (A few of these pyroclastic flows have created some really nice rock for climbing!)

Known Unknowns

As with El Malpais or the Jemez Caldera, it can be easy to think that The Gila’s hellfire is over and done with. Indeed, when you’re out there, you’re likely to get the impression that the only geological force in play these days is gradual weathering wrought by snowmelt, monsoon rains and the freeze-thaw cycle. Apart from scattered geothermal springs, the area seems to have passed into an indefinite dispensation of tranquility.

But let us not forget how little we know about the world beneath our feet. The crust of the Basin and Range is still stretching and thinning. Who can say for certain what blobs of mantle could be lying in wait? Waiting for the stars to align. Waiting to crack through the feeble doors of the crust’s infernal prison.

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(Today’s image is courtesy of the U.S. Geological Survey.)

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