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Mountain 101: Why are Colorado's highest peaks so high?
Mixing the Aspen Anomaly with free beer
John Fayhee

Afew years back, I found myself sitting at a table with a slew of academicians, almost all of whom had those intimating letters following their surnames: PhD. (Here I admit that I have no letters, intimidating or otherwise, following my surname. Feel free to read into that reality whatever you will.) The gathering, which I had no business attending except that I was drinking buddies with the caterer and he said there would be unlimited quantities of free beer — was transpiring at a small college located at least 150 miles from the next closest institution of higher learning. It was the kind of college where almost every faculty member is essentially a one-person department, a reality that can make for some maladroit social interaction, especially if that interaction is mixed with adult beverages.

I spent an enlightening half-hour listening to a philosophy professor and a geology professor attempt to establish something approximating common conversational ground. The former went off on a tangent that, once I cut through the obligatory intellectual haze, amounted to a verbal diatribe about how a poor reading of fate-versus-free-will had landed him at a small college in the middle of nowhere, while the latter countered with a series of observations about tectonic sublimination.

They spent the entire time frustratingly talking around each other, which was OK, since neither was listening to what the other was saying anyhow, which, if they had done so, maybe they would have realized that they were making the same arguments from different angles.

Finally, the philosophy professor exasperatedly ambled off to hit on some comely teaching assistants, who were talking about music preferences while obliterating the offerings on the buffet table and who, judging from their reactions to the philosophy professor’s slurred overtures, had their own take on the concept of fate versus free will. (They willingly egressed the premises, clutching much in the way of finger sandwiches.)

That left me with the geology professor, who, I learned after numerous cervezas, was an avid backpacker, which gave us something to talk about, though, predictably, he focused on on-foot jaunts through sedimentary striations, while I talked more about bong hits with fellow dirtbags deep in the woods. During that amicable chitchat I made casual mention of the fact that I know a grand total of one thing about his chosen vocation: there are igneous, metamorphic and volcanic rocks. Sadly, what the first two of those might be, well, who can say?

Awkward silence ensued.

So, I shifted to journalist mode by asking the somewhat forlorn professor what is one question he would like to be asked about the geology of Colorado, one that had never been posed to him before.

His eyes lit up, and he responded: “Why are the highest mountains in Colorado not shorter?”

OK, well, that’s one that never would have occurred to my liberal-arts brain.

He proceeded, at my behest, to address his own question. My ears perked up when the word “Aspen” passed his lips.

Here is what I learned (I should point out that, since we were both somewhat inebriated at this juncture, I felt compelled to verify the following information by way of a follow-up phone call): 

Given the age of Colorado’s highest mountains — the northern end of the Sawatch Range between Leadville and Aspen — why have peaks such as Mount Elbert (14,433 feet elevation) and Mount Massive (14,421) remained so high? After all, since the Terminator-like forces of erosion have been working their mountain-killing magic for more than 50 million years, those peaks ought to be less altitudinous, according to my geologist friend, who, by this point, was getting animated, sort of like a Baptist minister getting to the fire-and-brimstone part of his sermon. I had to resist the temptation to shout “hallelujah!”

Ends up that, at the northern end of something called the Rio Grande Rift — which, come to learn, extends all the way from Chihuahua to Leadville, with tendrils traveling to Paonia and Aspen — lies a geologic oddity called the “Aspen Anomaly.”

The Aspen Anomaly (named thus solely because Aspen has a greater international-recognition quotient than does Leadville, under which most of the Anomaly lies) is basically a large area of anomalously hot and thin mantle about 50 kilometers below the crust that is being pushed up by the Earth’s molten core at about the same rate as the northern Sawatch Mountains are eroding.


From a geological perspective, mountains are like icebergs, insofar as they have roots, and only a small percentage of their mass appears above the Earth’s surface. No matter their mass, they still basically float atop the warm upper mantle, which, while not liquid, is still viscous. Thus — and this is a hard one to grasp when you’re eyeballing Elbert and Massive — all mountains have a degree of buoyancy. That means they can be pushed upward by almost inconceivable forces many miles beneath the Earth’s surface.

The Aspen Anomaly was only discovered about 20 years ago, and geologists are studying it intensely even as we speak. But, already, those few members of the public who have even heard about it are wondering aloud if, given those ominous associated  words “pushed up by the Earth’s molten core,” the Aspen Anomaly has the same degree of super-volcano potential as does the infamous Yellowstone Anomaly.

Time (geologic time, that is) will tell.


In the meantime, the area surrounding Leadville and extending toward Aspen, at this moment of geologic history, finds itself sitting atop a bubble of viscosity large and strong enough to lift the state’s highest mountains even higher.

Which led me to ask my newfound geology professor chum a question of my own invention: 

In an elevation-crazy state like Colorado, almost everyone knows that the state’s highest peaks are the famed Fourteeners. But what was the highest mountain in the geologic history of Colorado?

According to my buddy, no one knows exactly, but there is zero in the way of doubt that, at one time, there were prominences in Colorado that were significantly higher than the lofty peaks that define the High Country today.

West Elk Peak, at 13,035-feet, the highest point in the 176,000-acre West Elk Wilderness (located basically between Gunnison and Paonia) is a stratovolcano — tall, conical volcanoes with many layers of lava, tephra (whatever that might be) and volcanic ash — that was active about 30 million years ago. Stratovolcanoes are characterized by steep profiles, and the lava that flows and hardens from these types of volcanoes tends to be extremely viscous; it cools and hardens before spreading far. Stratovolcanoes (Mount Fuji in Japan, and Mount Hood in Oregon are classic examples), have pretty much the same geometry, steepness of slopes and flanks that flatten out gradually, all of which allow geologists to calculate their probable height while they were still spouting lava towards the heavens.

Using calculations based upon the consistent profiles of stratovolcanoes, geologists have concluded that West Elk Peak was once more than 17,000 feet tall. (Using those same types of lava-dispersal calculations, geologists have determined that 14,411-foot Mount Rainier, the highest mountain in Washington State, was once about 16,000 feet high, while 12,637-foot Humphreys Peak, the highest point in Arizona, was once at least 15,000 feet high.)

Thing is, there are other stratovolcanoes in Colorado, primarily in the San Juan Mountains, that are significantly higher than West Elk Peak. One, 14,309-foot Uncompahgre Peak, is the sixth-highest mountain in the state. Though a peak-specific study has never been performed, if the same types of calculations used to determine how high West Elk Peak, Humphreys Peak and Mount Rainier used to be were applied to Uncompahgre Peak, it is estimated that, between 24 and 30 million years ago, it likely achieved a maximum elevation of about 20,000 feet. The same could likely be said about numerous other stratovolcanoes in the San Juan Mountains.

By then, the free beer was gone and it was time to wobble out into the High Country night, where, on the distant horizon, outlines of hulking topography could still be made out due to the cloud-free sky and the scores of dazzling stars.

RFWJ Editor M. John Fayhee is willing to sit through a monologue about geology if he gets free beer as a result.