SF-0022Myth or Evidence?
Nobody has settled how Devils Tower formed, and the Park Service says so
The rock is phonolite porphyry and the columns are cooling cracks — that much is agreed. How the magma got there is not. The NPS lists four origin hypotheses and says discrepancies remain for all of them.
Devils Tower from the south-west. The vertical fluting is columnar jointing — cracks formed as the igneous rock cooled and contracted — and it is the part of the story geologists agree on.
Devils Tower is a laccolith in the Black Hills of Wyoming. A laccolith forms when molten magma forces its way into a rock formation, then cools and hardens. As the surrounding rock erodes away, the hardened former magma remains.
- Image
- Alex Demas
- Taken
- 2015-07-11
- Location
- Devils Tower National Monument, Crook County, Wyoming
- Archive ref.
- USGS media library — IMG_1998
- Licence
- Public domain per the USGS media library's item-level Sources/Usage statement (licence record)
- The image itself
- Authentic, unaltered
Devils Tower, Wyoming. Alex Demas, US Geological Survey media library, 11 July 2015. Public domain. Cropped.
Verdict
"It's a volcanic plug. The volcano eroded away and left the hard throat behind."
The individual facts may check out, but the way they are framed leads to a false conclusion.
Every element of the claim is plausible and the framing is what fails: it presents one candidate as the settled answer, and the effect on a reader is that they now believe the question is closed.
ESTABLISHED, and not in dispute here: the rock is igneous. The NPS Geodiversity Atlas states "The crystalline igneous rock that composes Devils Tower is classified as phonolite porphyry", records columns "1.8–2.4 m (6–8 ft) in diameter at their base" tapering "to about 1.2 m (4 ft) at the top", and gives the Tower as rising "about 386 m (1,267 ft) above the north-flowing Belle Fourche River". Columnar jointing is cooling contraction, and the Park Service describes the Tower as "full of natural cracks created by columnar jointing".
NOT ESTABLISHED: how the magma was emplaced. The Atlas lists four hypotheses — an erosional remnant of a volcanic neck; a remnant of a laccolith or sill; an intrusive body such as a small pluton; and a body sitting in a depression that is "the remnant of a crater formed during an explosive volcanic episode". It then says, in its own words: "apparent discrepancies still exist for all of the origin hypotheses."
So "it is a volcanic neck" is not false. It is one of four, stated as though it were one of one. The image is authentic and the photographer is credited below; nothing is wrong with the picture or the rock. What misleads is the confidence.
Misleading requires 1 primary or authoritative source. This file cites 3.
In short
Devils Tower is routinely introduced as the eroded neck of an ancient volcano. That is one of at least four explanations the National Park Service records, alongside a laccolith or sill, a small pluton, and the remnant of an explosive crater. The agency that manages the monument writes that "apparent discrepancies still exist for all of the origin hypotheses." What is settled is the rock and the columns; what is not settled is how a body of magma came to be standing 386 metres above the Belle Fourche River.
What is actually settled
The rock is phonolite porphyry — igneous, crystalline, intruded as magma. The fluting that makes the Tower look machined is columnar jointing: contraction cracks formed as that magma cooled, splitting it into columns 6 to 8 feet across at the base and tapering to about 4 feet at the top. The whole thing stands about 386 metres above the Belle Fourche River, on the north-west flank of a Black Hills uplift raised 45 to 65 million years ago.
None of that is in dispute. It is a great deal to know about a rock.
What is not
How the magma got there.
The National Park Service’s own Geodiversity Atlas lists four candidate explanations. That the Tower is:
- an erosional remnant of a volcanic neck — the throat of a volcano that reached the surface;
- a remnant of a laccolith or sill — magma that spread between layers and never erupted;
- an intrusive igneous body, such as a small pluton;
- the fill of a crater — a body sitting in “a depression that is the remnant of a crater formed during an explosive volcanic episode”.
And then the sentence that makes this a file:
However, apparent discrepancies still exist for all of the origin hypotheses.
All of them. Not “the second is favoured”, not “the debate has narrowed”. The agency that manages the monument records that every available explanation has something wrong with it.
The version you have probably heard
“It’s a volcanic plug” is candidate one, stated as though there were no candidates two, three and four. It might be right. What it cannot honestly be is confident.
And the habit is not confined to tour guides. The photograph on this file comes from the USGS media library, where the caption underneath it reads:
Devils Tower is a laccolith in the Black Hills of Wyoming.
That is candidate two, asserted flatly, on a federal science website, with no caveat at all. Two government sources, two different single answers, one of them explicitly saying elsewhere that no single answer survives scrutiny.
What this file does not claim
That the volcanic-neck explanation is wrong — it is the first one the Park Service lists.
That geologists are baffled. They are not; the open question is narrower than that, and it is specifically about the mode of emplacement, and about whether this magma ever reached the surface at all.
And it does not claim to know what the discrepancies are. The NPS says they exist for all four and does not say what they are, and no source consulted here itemises them. That is the honest shape of this one: the question is open, and this file cannot tell you why each answer falls short — only that the people who would know say they all do.
The evidence
The rock is identified without qualification: "The crystalline igneous rock that composes Devils Tower is classified as phonolite porphyry."
Cited sources:S1
The columns are cooling structures and the Park Service describes the Tower as "full of natural cracks created by columnar jointing." Their dimensions are recorded: "1.8–2.4 m (6–8 ft) in diameter at their base and taper gradually upward to about 1.2 m (4 ft) at the top."
The scale: the Tower "rises about 386 m (1,267 ft) above the north-flowing Belle Fourche River", with a summit elevation of "1,560 m (5,117 ft) above sea level".
Cited sources:S1
Four origin hypotheses are listed by the NPS Geodiversity Atlas, not one: that the Tower is "an erosional remnant of a volcanic neck"; "a remnant of a laccolith or sill"; "an intrusive igneous body, such as a small pluton"; and that it "lies in a depression that is the remnant of a crater formed during an explosive volcanic episode".
Cited sources:S1
None of them is clean. The Atlas states: "However, apparent discrepancies still exist for all of the origin hypotheses."
Cited sources:S1
The regional setting is dated even where the Tower's emplacement is not: Devils Tower "is located on the northwest flank of the Black Hills, an uplift formed during the Cretaceous–Tertiary mountain-building episode called the Laramide Orogeny that occurred about 45–65 million years ago."
Cited sources:S1
Federal sources do not speak with one voice on this, which is part of why the single-answer version travels. The USGS media library item used for this file's photograph states as its caption: "Devils Tower is a laccolith in the Black Hills of Wyoming" — a flat assertion of one of the four hypotheses, with no caveat, on the same government domain.
Cited sources:S3
Evidence that cuts the other way
Findings that complicate or argue against the verdict above. They are listed because leaving them out would make the file look stronger than it is.
The volcanic-neck explanation is not a myth and this file does not treat it as one. It is the first hypothesis the NPS Atlas lists and it remains a live candidate. The verdict is about stating it as settled, not about whether it might turn out to be right.
Cited sources:S1
This file does not establish what the discrepancies actually are. The Atlas says they exist for all four hypotheses; it does not itemise which problem attaches to which explanation, and no source read here does. That is why the verdict is Misleading rather than Unresolved — an Unresolved verdict here would require naming at least two serious explanations together with what each fails to account for, and those specifics were not obtained.
Cited sources:S1
Nothing here suggests geologists are baffled. A great deal is settled — the rock type, the cooling history recorded in the columns, the regional uplift, the erosional exposure. The open question is narrower than "how did this form": it is which mode of emplacement put the magma where it is, and whether it ever reached the surface.
Cited sources:S1
What we still don’t know
- What the discrepancies are. The NPS states that they exist for all four hypotheses and does not say what they are, and no source read here itemises them. This file therefore reports that the question is open without being able to explain why each candidate falls short — which is a real limit on how satisfying it can be.
- The age of the intrusion itself. The Atlas dates the regional Laramide uplift to about 45–65 million years ago; it does not, in what was read here, give a date for the emplacement of the Tower's magma, and none is asserted.
- Whether the magma ever reached the surface. This is the substance of the disagreement — a volcanic neck implies it did, a laccolith or pluton implies it did not — and nothing read here settles it.
- How the number of hypotheses is counted. The Atlas lists four; other NPS material groups them as three by combining the intrusive cases. This file uses the Atlas's four and notes that the grouping is a matter of presentation rather than a disagreement about the geology.
- The cultural dimension is deliberately out of scope here and is not an open question so much as a different subject. The monument is sacred to several Northern Plains tribes and is known by names including Bear Lodge; this file is about a geological claim and makes no claim about the site's cultural status, its naming, or the practices associated with it.
Sources
Every source below was read in full before it was cited. Archive snapshots are recorded at research time, because a file whose sources have evaporated is indistinguishable from one that never had any.
S1Tier 1Read in full
NPS Geodiversity Atlas — Devils Tower National Monument, Wyoming
National Park Service
The managing agency's geological account, and the spine of this file. Establishes the rock as phonolite porphyry; the column dimensions at base and top; the height above the Belle Fourche River and the summit elevation; the Laramide setting of the Black Hills at 45–65 million years; the four origin hypotheses in the agency's own wording; and the decisive sentence that "apparent discrepancies still exist for all of the origin hypotheses." Cited for text only. NPS image rights are not uniform and no NPS image is used by this file.
S2Tier 1Read in full
Geologic Formations — Devils Tower National Monument
National Park Service
The park's own page, cited for two things: that the Tower "is full of natural cracks created by columnar jointing", and — by what it does not do — that the park describes the Tower as "a geologic oddity of epic proportions" and defers the formation story to a separate page rather than stating a single answer on the main geology page.
S3Tier 1Read in full
Devils Tower — USGS media library item
Alex Demas · US Geological Survey · 2015-07-11
The image's rights record, and separately a piece of evidence in its own right. Establishes the item-level "Sources/Usage: Public Domain." statement and the photographer credit — read a second time for literal text, which established that no agency name is printed in the credit block and so narrowed this file's public-domain basis. It is also cited for its caption, "Devils Tower is a laccolith in the Black Hills of Wyoming", which is a federal source asserting one contested hypothesis as fact and is quoted here as an instance of the framing the file is about.
Checked for circularity: S1 and S3; S2 and S3 were confirmed not to derive from one another. Two sources that trace back to the same origin are one source, and counting them twice is the most common way a false claim looks well-evidenced.
How we checked this
What we went looking for, and what we found
Four checks, two of which changed the file and one of which changed the verdict.
First, on the verdict itself. Unresolved was the obvious choice and was rejected, because the standard for it requires naming at least two serious explanations together with what each fails to account for. The NPS says discrepancies exist for all four hypotheses without itemising them, an attempt to retrieve USGS Bulletin 1021-I "Origin of Devils Tower" through the NPS park-history library returned an unrelated page, and inventing per-hypothesis objections would have been exactly the fabrication the format exists to prevent. Misleading is the honest verdict: the framing produces a false conclusion, and that can be shown without knowing the internal objections.
Second, against treating the volcanic-neck story as a myth. It is the first hypothesis the NPS lists and may well be correct. The file says so, and the verdict is about confidence rather than content.
Third, against implying geologists are lost. The rock type, the cooling history in the columns, the regional uplift and the erosional exposure are all settled. The open question is narrower than the headline could be made to sound, and the body says what it actually is.
Fourth, on the image, where the finding was unexpected. The USGS media item chosen for its photograph carries a caption asserting a different single answer — "Devils Tower is a laccolith" — with no caveat. Rather than quietly not quoting it, it is recorded as the originalCaption, cited as evidence, and disagreed with in the body, because a federal source stating one hypothesis as fact is part of why the single-answer version travels at all.
- We searched for evidence against our own conclusion
- We traced where the claim started
- The claim is stated in its strongest form, not a weak version
- The photograph was verified independently of the story
- We checked whether this was settled after the popular version froze
- Image rights were traced to a stated licence
- We checked what we were leaving out
- The verdict sat before publication, and was re-read cold
- Confidence in the verdict
- high
- Verdict assigned
- Most recent authoritative source
- Researched by
- The Strange File
COOLING-OFF PASSED 2026-08-01. The verdict was assigned 2026-07-31 and the wait has elapsed. The fresh-eyes pass was made by a session that neither researched nor wrote this file, re-reading the dossier, the evidence, the sources, the verdict reasoning, the rights record and the Quick File cold. Nothing required changing. The headline attributes the open question to the Park Service, which is whose position it is: four origin hypotheses listed, and "apparent discrepancies still exist for all of the origin hypotheses."
That pass is cooling-off and nothing else. Cooling-off, independent review and the owner's approval remain three separate controls and none may stand in for another. No independent review has occurred; this file carries no sensitivity flag, so none is required. The owner has not approved publication, and READY is not permission to publish.
No sensitivity flag, and this one was considered carefully rather than waved through. Devils Tower is sacred to several Northern Plains tribes, is known by other names including Bear Lodge, and is the subject of a long-running dispute about its official name and about climbing during the June ceremonial month. None of that is the subject of this file, which adjudicates a geological claim using two federal agencies' own words, names no community's position, and makes no claim about naming, access or practice. The cultural dimension is recorded in the uncertainties as out of scope rather than left unmentioned, because silently omitting it would imply it does not exist.
The only individual named is the photographer, credited because the source credits him.
Part of a collection
The Correction OvershootsDebunking has a second error, and almost nobody guards against it.
What The Record Declines To SayAn authority’s silence, treated as evidence rather than as a gap.
The Record Disagrees With ItselfTwo authoritative sources, both public, and they do not agree.
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