Wyoming
Wyoming’s Heart Mountain Formed By The Two Largest Landslides In Earth’s History
Cody’s Heart Mountain isn’t the result of one of the largest known landslides in Earth’s history. It’s the result of two of the largest landslides in Earth’s history separated by nearly 50 million years.
There’s a lot that makes Heart Mountain, the iconic peak north of Cody in Park County, unique in the geological context of Wyoming. That’s saying a lot, considering the Cowboy State is one of the world’s most lauded geological wonderlands.
It’s a story of a block of rock the size of Rhode Island moving at 700 mph, an eruption of the Yellowstone supervolcano, and two separate but equally cataclysmic events in Earth’s geologic history.
Thomas Bown and Albert Warner are the authors of “The Heart Mountain Detachment: A Critical Reappraisal,” which was published in February.
It’s a comprehensive look at the geology of Heart Mountain that presents a new interpretation of how it came to be, revealed by the complex geological landscape and evidence scattered across the northwest corner of Wyoming.
Their conclusion is that it took less than 30 minutes to make Heart Mountain, but that 30 minutes was stretched across 47 million years.
“We believe that Heart Mountain constitutes the world’s largest known landslide, but there are two different structures from two different events,” Bown told Cowboy State Daily. “They’re contiguous but separate. It’s complicated.”
The World’s Largest Landslide
Heart Mountain is a geological anomaly for several reasons. For one, the rock at the top of its iconic peaks is significantly older than the rock at its base, violating the geological law of superposition.
Also, the mountain belongs nearly 50 miles northwest of Cooke City, Montana. All the evidence indicates that the geology of Heart Mountain is a massive block of Bighorn Dolomite that was initially attached to the rest of the formation exposed along the Wyoming-Montana state line at the northern extent of the Absaroka Range.
So, how did it get from Cooke City to Cody?
“The debris of Heart Mountain constitutes the world’s largest landslide,” Bown said. “A block of Bighorn Dolomite that was the size of the state of Rhode Island rafted about 40 miles from its source around 49 million years ago.”
Calling this event a “landslide” understates its enormity. The state-sized slab of Paleozoic sedimentary rock moved at 100 meters a second, covering over 40 miles in less than 30 minutes at speeds over 700 mph, leaving behind a field of “mountains” and other debris across an expanse over 40 miles long and 15 miles wide.
“We believe it was caused by a massive subduction zone earthquake, 9.0 or higher,” Warner said. “An earthquake of that intensity would have lasted from 4 to up to 10 minutes.”
An earthquake of that length and intensity would have reduced the surface friction to the point where it barely existed. Bown compared the incredible geological phenomenon to an electric tabletop football game.
“The blocks skidded across the landscape like the football men on the field,” he said. “Paleomagnetic studies have shown that the massive block broke, and those individual blocks rotated as they went. It was like a vibrating conveyor belt.”
The “Heart Mountain Detachment” came to rest at the present-day location of Pat O’Hara Mountain, the prominent peak directly west of Heart Mountain, where 500-million-year-old limestone and dolomite sit on top of 55-million-year-old mudstone and shale. It took less than 30 minutes for the blocks to cover a distance of nearly 40 miles.
It’s hard to visualize the scale of this event, but the evidence of it is spread throughout northwest Wyoming. Many of the “mountains” visible from the pinnacle of Dead Indian Pass are pieces of the Rhode Island-sized block of Bighorn Dolomite that broke off and settled during the landslide.
“One of the more recognizable features along the Chief Joseph Highway is the Cathedral Cliffs,” Warner said. “That’s one of the largest breakaway blocks from this landslide. Republic Mountain right outside Cooke City is another one of these blocks.”
But, according to Bown and Warner, that event didn’t create modern-day Heart Mountain. It stopped just short of reaching that spot and needed another unprecedented geological event to finish the job.
Another One?
This is where the story of the Heart Mountain Detachment usually ends – a single event that occurred 49 million years ago. Bown and Warner believe there’s more to this story.
Their new book focuses on the bigger picture of the world’s largest landslide. They believe the McCullough Peaks, south of Cody, indicate another cataclysmic event that was associated with but not attached to what’s been understood as the Heart Mountain Detachment Fault.
“McCullough Peaks was believed to be part of the Heart Mountain Detachment Fault, but that’s all early Eocene in age,” Bown said. “The deposits around McCullough Peaks are all early Pleistocene in age. They both have older rocks sitting on younger rocks, and they’re contiguous, but they sit on surfaces of very different ages.”
After studying the existing research and geology of the region, Bown and Warner concluded that there’s a distinct difference between the two deposits. That indicates that another event must have occurred to create the McCullough Peaks.
“It’s completely different and separate from what most people consider the Heart Mountain detachment fault,” Bown said. “The mountain itself is not part of the fault. There’s one structure beginning near the eastern edge of Yellowstone National Park and going all the way east of McCullough Peaks. Now we believe that’s the result of two structures, separated in time by 47 million years.”
In their book, Bown and Warner present their evidence for two different events: the Shoshone/Sunlight/Abiathar Detachment Fault, which created Heart Mountain 47 million years ago, and the Heart Mountain/McCullough Peaks Sturzstrom, a rock avalanche that only occurred around 2 million years ago.
Warner said these were “contiguous but separate events” with similar outcomes. Both involved enormous landslides that led to the creation of mountain ranges, but the 47-million-year difference makes all the difference.
“We believe that an earthquake of great intensity generated the older movement in the Eocene,” he said. “The younger movement, the one that created the actual Heart Mountain and McCullough Peaks deposits, happened during an immense volcanic eruption accompanied by earthquakes that took place about 2 million years ago in the Pleistocene.”
What was the source of “the younger movement?” Look no further than the supervolcano next door.
The Caldera Culprit
The source of the 49-million-year-old landslide earthquake is still disputed. It was possibly caused by “frictional heating” associated with plate tectonics, as magma deep under the Earth’s surface heated and lifted the dolomite, causing the Rhode Island-sized detachment.
Meanwhile, Bown and Warner think the source of the 2-million-year-old landslide earthquake can be directly traced to the volcanic hotspot that moved into northwest Wyoming during the 47-million-year gap between the geologic events.
“That was the result of silicic eruptions in Yellowstone National Park that resulted in the collapse of the caldera,” Bown said. “It was probably the most violent volcanism in the history of that range.”
Around 2.1 million years ago, the Yellowstone caldera underwent one of the largest eruptions in its history. It occurred right when the volcanic hotspot burned its way into the northwest corner of Yellowstone National Park.
Over 590 cubic miles of ash were ejected from the caldera, creating a layer of volcanic ash known as the Huckleberry Ridge ash bed. It stretches as far south as the Mexican border, as far north as the Canadian border, and across the Western U.S. from southern California to the Mississippi River.
An eruption of that intensity would have generated devastating earthquakes in its vicinity. A modern-day analogy would be the landslides and other events prompted by the eruption of Mount St. Helens in 1980, only on a much larger scale.
This incredible event is what Bown and Warner believe created Heart Mountain as it exists today.
Their research concluded that the original detachment ended in the Absaroka Mountains. The massive blocks that became Heart Mountain and McCullough Peaks didn’t descend to their current locations until the Yellowstone eruption 2.1 million years ago.
“The easternmost remnants of the Shoshone/Sunlight/Abiathar Detachment Fault came to rest in the area of the Natural Corral, north of Pat O’Hara Mountain,” Bown said. “They piled up and sat there for 47 million years, and then an immense volcanic eruption caused this mass to break away and sweep down the Shoshone River as a landslide.”
That would mean that Heart Mountain, which is composed of 500-million-year-old rock sitting on 50-million-year-old rock, is a massive breakaway of a much more massive block from a 49-million-year-old landslide but only reached its current location around 2 million years ago.
Two From One
If all these intricacies seem complex and confusing, welcome to the complexity of geology. The “controversial” takeaway from Bown and Warner’s research is that Heart Mountain wasn’t formed as part of the Heart Mountain Detachment Fault.
“The debris from the Heart Mountain/McCullough Peaks Sturzstrom is very different from the Shoshone/Sunlight/Abiathar Detachment Fault, which is an almost completely unique structure,” Bown said. “Both were earthquake-generated but have very different internal structures and mechanisms.”
Their research indicates that Heart Mountain wasn’t the result of a single event, but two separate events of similar scale. Bown and Warner recognize that their interpretation will shake up the accepted explanation for the geologic events that led to modern-day Heart Mountain.
“There’s always more that you can study, so we can learn more about what happened,” Bown said. “With additional study, you can learn more about the speed, internal mechanics, and movement of these landslides, which isn’t completely known today.”
Landslides and sturzstroms are relatively common in the present day and geological history, but not on the scale of what occurred in northwest Wyoming twice in 50 million years. Fortunately, many geologic processes look and behave similarly, even if their scales are immensely different.
Warner is examining possible analogies for the events in the Philippines. Insight into similar events from the past and any possible events in the future could reveal more information on what happened in northwest Wyoming 49 million years ago, and again 2 million years ago.
“The Philippine Area is an incredibly active tectonic region, so earthquakes there are very, very common,” he said. “There is a study of a particular block of Miocene rock that broke away and created a strip surface very similar to the surface of tectonic denudation originally described around Heart Mountain. A very similar situation, but on a much smaller scale.”
Natural Monuments
A lot has changed in the 50 million years since the initial detachment that led to the formation of the modern-day landscape in northwest Wyoming. Evidence that could reveal more about these incredible events has been lost to the inevitable passage of time.
“Part of the problem of studying the Shoshone/Sunlight/Abiathar Detachment Fault is that it immediately preceded a period of enormous deposition,” Bown said. “It happened right before the beginning of volcanicity and tremendous buildup of volcaniclastic sediments in the Absaroka Range, so much of that evidence has been buried.”
Meanwhile, the evidence of the Heart Mountain/McCullough Peaks Sturzstrom is eroding and readily available for scientific scrutiny. Bown and Warner hope their book will increase interest in the area and challenge more geologists to scrutinize their work and the geology that led them to their conclusions.
The geologists also hope that more people become aware of these incredibly dramatic stories of unprecedented catastrophes and mountain-building that created the striking landscapes in and around Cody, Cooke City, and Yellowstone National Park.
When someone looks upon the iconic peak of Heart Mountain, they aren’t looking at a traditional mountain. They’re glimpsing the result of the largest known landslides in Earth’s history — a massive mountain that’s just a small part of a much grander story scattered across the region.
“One of the things Tom and I have discussed is that there’s nothing about the geology posted at the summit of Dead Indian Pass,” Warner said. “We would love to see some geological recognition at that particular site, because there are a lot of natural monuments to these events. When you recognize what occurred there, it’s truly spectacular.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
Wyoming
(LETTERS) Wyoming Supreme Court judges, congressional responsibility, pregnancy and US involvement in the Middle East
Oil City News publishes letters, cartoons and opinions as a public service. The content does not necessarily reflect the opinions of Oil City News or its employees. Letters to the editor can be submitted by following the link at our opinion section.
Wyoming Supreme Court judge process better than federal’s
Dear Casper,
This letter is in response to Mr. Ross Schriftman’s letter to the editor from April 11. His opinion appears to be that the Wyoming process of selecting Wyoming Supreme Court justices is somehow flawed. Justices are selected through a merit-based assisted appointment process. When a vacancy occurs, a seven-member Judicial Nominating Commission recommends three candidates to the governor, who appoints one.
Appointed justices serve at least one year before standing in a nonpartisan retention election for an eight-year term.
The commission consists of the chief justice as chair/tie-breaker, three attorneys selected by the Wyoming State Bar and three non-attorneys appointed by the governor. The governor must select one of the three nominees provided by the commission to fill the vacancy.
After serving at least one year, justices stand for retention in the next general election. Voters cast a “yes” or “no” vote. If retained, the justice serves an eight-year term.
Candidates must be U.S. citizens, Wyoming residents for at least three years, licensed to practice law, and have at least nine years of legal experience. Justices must retire at age 70.
U.S. Supreme Court are appointed for life!
I would offer that the Wyoming process is superior to that of the U.S. Constitution. Voters are involved the process, which we are not at the federal level.
Wyoming justices can be impeached and removed from office by the state House of Representatives and Senate.
Michael Bond
Casper
Wyoming delegation must answer for President Trump’s Iran policy
Dear Casper,
Sent this to each of our Wyoming congressional delegates. I lived in Montana for years. These are the questions the Daily Montanan asked of their elected congressional representatives.
I ask the same questions of our Wyoming delegation. Montana got no answers. I doubt that we will either.
- President Donald Trump has continued to threaten to hit targets that would affect or kill civilians in Iran. Do you support his stated objectives and deadlines?
- Are you concerned that some of these targets could be construed as attacking civilians and therefore become war crimes?
- Do you have any concerns about wiping out an entire civilization, as Trump has threatened?
- If these are only rhetorical threats, what does that do to our stature in the world when we make threats, but don’t follow through with them?
- Polls have continued to show more than a majority of Americans do not support the efforts against Iran. Why do you support the effort?
- If you do not support the effort in Iran, at what point would you support Congressional intervention or oversight on the issue?
- Have you been briefed and do you believe that there are clear objectives in this war with Iran, and how can you communicate those with your constituents?
- The U.S. has repeatedly criticized Vladimir Putin and Russia for its invasion and treatment of the Ukrainian people and it sovereignty. How does that differ from America’s “excursion” into Iran?
- What is your message for Montanans who are seeing gas prices and the cost of living generally increase?
- Last week, President Trump said that America doesn’t have enough money for healthcare and childcare; further, those things must be left to the individual states in order to fund the military? Do you agree?
- President Trump continues to boost military budgets and request additional funding for the war in Iran. Do you support these?
Tami Munari
Laramie
Pregnancy is personal, not political
Dear Casper,
The recent Wyoming Supreme Court ruling, which affirmed abortion is health care, has caused some who disagree with the ruling to attack Wyoming’s judicial system.
In an opinion letter, candidate Ross Schriftman facetiously writes, “…our God-given First Amendment right of free speech does not apply when criticizing our fellow citizen judges.”
This is the first flaw in his logic because the Constitution was not written by God, therefore the right of freedom of speech was thought up and written by men. God is not the author nor guarantor of personal freedoms — our Constitution and judicial system are.
The second flaw in his argument references a letter signed by 111 professionally-trained, experienced, and well-respected Wyoming judges and attorneys explaining how the courts arrive at their rulings. It is illogical to claim we are all “citizen judges” because even though citizens have a constitutionally-guaranteed right to an opinion, it does not make every citizen a legal expert. The judges’ and attorneys’ excellent letter speaks for itself.
Mr. Schriftman claims the Supreme Court, “… create(d) an absurd definition of health care to include the intentional murder of pre-born human persons; something they did to justify overriding the equal protection clause… .” This logic is flawed because it is based on a conflation of an obsession with “pre-born human persons” and equal protection under the law.
There is significant disagreement on the issue of fetal personhood and who gets to determine it: the doctors? the lawyers? the pregnant woman? the anti-choice crowd?
Many understand and appreciate it has taken women almost 200 years to gain and keep Equal Protection Under the Law, and the disagreement over who is legally, materially, and morally responsible for a fertilized human egg has always been part this historical struggle. But it was the Roe v. Wade Supreme Court decision that finally established a constitutional right, for women and men, to private health care decisions and, since pregnancy is a health condition, that included abortion.
Even though it wasn’t explicit, Roe also effectively affirmed that bestowing of “personhood” is a private determination to be made by the pregnant woman and her God. But, sadly, here we are again, dealing with folks who mistakenly believe they have a right to interfere in someone else’s pregnancy.
The Rev. L Kee
Casper
Why does the U.S. keep troops in oil producing countries?
Dear Casper,
There are two facts that don’t ever seem to be considered by our government that cost us dearly.
Osama Bin Laden said the stationing of U.S. troops in the Middle East was the reason Al Qaeda attacked us on 9/11. Does the U.S. believe that the oil producing countries in the Middle East will only sell us oil if we force them to by stationing troops there? I’m not aware of any other countries that believe that.
The other fact is, the U.S. is the only country to ever use a nuclear weapon offensively. There are several countries that have nuclear weapons, including North Korea. The reason countries have been reluctant to use nuclear weapons is MAD, mutually assured destruction. Consequently, is it reasonable to expect Iran, should they develop a nuclear weapon, to attack the U.S., knowing that our superiority in nuclear capability would assure the complete destruction of their country? It clearly would be suicidal for them to do so.
But, just to be cautious, rather than destroying the entire country to deter Iran from acquiring a nuclear weapon, wouldn’t it make more sense to destroy their nuclear infrastructure?
Bill Douglass
Casper
Related
Before they ever left Earth, all of NASA’s Artemis II astronauts trained with the National Outdoor Leadership School (NOLS) — and for some, that preparation included long days navigating Wyoming’s backcountry.
That NOLS training was singled out by Artemis II Commander Reid Wiseman Thursday during the crew’s first group interview from NASA’s Johnson Space Center in Houston, Texas, after returning to Earth on April 10 from it’s 10-day mission to the moon and back.
He reflected on decision-making under pressure and how lessons learned through NOLS resurfaced during moments of stress and distraction.
“There’s a saying that we learned from one of our National Outdoor Leadership School instructors: integrity is not a one or a zero,” Wiseman said. “You can be in integrity, and you can be out of integrity — and I’ll be the first to admit that there were moments when I was out of integrity because sometimes the view or the human experience would just pull me away from the work.”
The partnership reflects a longstanding relationship between NOLS and NASA, the United States’ civilian space agency, and the Lander-based outdoor education organization.
Since 1999, NASA has worked with a variety of organizations and contracted NOLS for more than 45 wilderness expeditions designed to help astronauts prepare for the realities of long-duration spaceflight.
Those expeditions place crews in remote, resource-limited environments where communication, leadership and teamwork become essential for safety — conditions that mirror life inside a spacecraft.
In 2023, Cowboy State Daily chronicled the Artemis II astronauts training in the Cowboy State. At the time, the connection between Wyoming’s wind-carved wilderness and the engineered isolation of deep space felt philosophical.
Now, after completing their mission, the astronauts say the lessons they learned in Wyoming followed them all the way to lunar orbit.
From Wyoming Backcountry To The Moon
For NOLS instructors, the connection between wilderness leadership and spaceflight comes down to a single idea, what the school calls “expedition behavior.”
Rick Rochelle, senior faculty and leadership coach at NOLS, told Cowboy State Daily on Friday that the concept explains why NASA continues to partner with the organization decades after the relationship began.
“There’s a phrase that NOLS calls ‘expedition behavior,’ and that is clearly the most important part of why NASA works with us and how it translates,” Rochelle said.
The term was coined by NOLS founder Paul Petzoldt, a mountaineer who set an altitude record on K2 in 1938, served in the 10th Mountain Division during World War II and later built the school around the idea that leadership is defined by responsibility to others.
“He said it’s an awareness of others’ needs and the character to make those needs as important as your own,” Rochelle said. “It’s really about how to be a great team member.”
Lynn Petzold, also senior faculty at NOLS, said astronauts who train with the school are placed in situations where leadership theory becomes practical experience — where decisions must be made under stress, and reflection becomes part of daily operations.
“NOLS provides experience for astronauts to go through leadership theory, work under stress, and reflect and debrief — extracting the learnings from the day and implementing them moving forward,” Petzold said. “That’s how you continue to grow and become a better team.”
The wilderness setting itself plays a critical role.
Long stretches in remote terrain force participants to manage fatigue, communicate clearly and make decisions without outside support. These are conditions that closely resemble life inside a spacecraft.
“This ties to the previous question, which is being in an austere environment for long periods away from distractions,” Rochelle said.
Why Wyoming Keeps Showing Up In Spaceflight
The connection between Wyoming and human spaceflight has grown steadily over the past quarter century, turning Lander into an unlikely but consistent training ground for astronauts preparing to leave Earth.
In the Wyoming backcountry, that might mean navigating a sudden weather shift or managing exhaustion miles from the nearest road.
In space, the same principles scale to orbital mechanics, life-support systems, and the psychological weight of isolation.
For instructors who have watched astronauts move through Wyoming’s mountains and deserts, the pride in the Artemis II mission is personal, Rochelle said.
“These are amazing human beings,” he said. “They love each other. They’re mission-focused, and they clearly want to have a positive impact on all of humanity.”
Petzold agreed.
“These are awesome human beings who were excited to be part of this mission,” she said. “They had a lot to contribute as individuals, and as a group they really brought it together.
“NOLS is just really excited and proud to work with NASA and this crew to pave a new path forward as we return to the moon. We’re proud to have been a small part of it.”
The same training that teaches students to read about weather, manage fatigue and support teammates in the Wind River backcountry is now helping shape how astronauts operate in deep space.
Kolby Fedore can be reached at kolby@cowboystatedaily.com.
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