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What is it?

A mountain in the Zagros range in Isfahan province, about 1.5 kilometers south of the Natanz enrichment complex, with a large facility dug into it.

The name is a small accident of translation. The mountain is called Kuh-e Kolang Gaz La, and kolang means pickaxe, so foreign analysts began calling the site Pickaxe Mountain. It is not what Iranians call the facility, and Iran has never given it a public name at all.

Why was it built there?

Because of the rock. Most of the surrounding range is sedimentary, but this mountain is hard, dense granite, which gives anything tunneled beneath it substantial natural protection.

Construction began in the autumn of 2020, months after an explosion destroyed an above-ground advanced centrifuge assembly plant at Natanz in an attack widely attributed to Israel. Iran said at the time that the underground halls would replace it.

The destroyed plant had been built to assemble roughly 6,000 advanced centrifuges a year, a capacity sized for the tens of thousands Iran expected to need as restrictions under the 2015 nuclear deal expired between 2025 and 2030.

What is inside?

Nobody outside Iran knows, which is the heart of the problem.

The International Atomic Energy Agency has never been given access. A double security perimeter, a fence and a wall with a patrol route, rings the entire mountain and joins Natanz’s own perimeter. There are two pairs of tunnel entrances, one on the east side and one on the west. Analysts assume they lead to a single facility, but even that is not certain.

Iran has said the site is for producing and assembling advanced centrifuges. The Institute for Science and International Security, which has tracked the construction by satellite for years, judges the space beneath the mountain large enough to hold considerably more: not only an assembly plant but a working enrichment plant capable of producing weapons-grade uranium, and probably enough room for weaponization work such as casting uranium metal and shaping it into weapon components.

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Two further claims circulate, neither verified. One is that part of Iran’s stockpile of uranium enriched to 60 percent, estimated by the IAEA at around 440 kilograms, has been moved there.

The other, from an Israeli intelligence assessment reported by the Wall Street Journal, is that thousands of centrifuges were moved into the mountain last autumn. Neither Israel nor the United States has published evidence.

The institute’s reading of the imagery is that the facility is not yet operational, and that construction continues.

How deep is it?

At least 100 meters beneath the mountain, which stands 1,608 meters above sea level.

There is a detail in those measurements worth noticing. The eastern entrances sit about 145 meters below the ridge; the western entrances about 100 meters. That 50-metre difference between the two sets of doors suggests the facility may have more than one level.

Either way it is deeper than Fordow or Natanz, both of which the United States has bombed.

Could American bombs destroy it?

Not the mountain itself. The GBU-57, the largest conventional bunker-buster in the US arsenal, weighs about 13,000 kilograms and is reported to penetrate 18 meters of concrete or 61 meters of earth. Against 100 meters of granite, experts are skeptical.

But a buried facility still has to breathe, and that is where the vulnerability lies. Any working complex needs power, ventilation, heating and cooling, deliveries and people going in and out, and each of those connections surfaces somewhere.

There is a precedent for exactly this. Schematics have been published for two other Iranian tunnel sites built by the Amad nuclear weapons program, Fordow and Shahid Boroujerdi. Both showed ventilation shafts, and in both cases those shafts were directly targeted in air strikes, in June 2025 and March 2026 respectively, because they offered penetrating weapons a way further inside.

No schematics for Pickaxe Mountain have surfaced publicly, but a probable ventilation shaft near the eastern entrances was seen under construction in 2024, fed by a power line that runs above ground before disappearing underground.

The institute’s assessment is that an attack would most likely aim at the power supply, the ventilation shafts and the open tunnel mouths, and it notes that as of imagery from July 9 the western pair of entrances remained open.

It also notes that hitting the hardened portals alone would probably deny Iran access only temporarily, adding the mountain to the list of sites that then have to be watched for attempts to dig back in.

Air defenses are not seen as an obstacle. Israel overcame them at Natanz in the opening hours of the June 2025 war.

The other way in

There is a second possibility, and it has history behind it.

The institute judges that the site, as it now stands, would be more suitable for attack or sabotage by ground forces than from the air. Its model is the 2020 destruction of the Natanz assembly plant, which reportedly involved explosives brought into the building during its construction.

Pickaxe Mountain is still under construction.

What does Iran say?

That there is nothing there to bomb. Foreign ministry spokesman Esmail Baghaei said in July that “no nuclear activity is taking place” at the site and called the American threats “a fabricated pretext for aggression, destruction, and sabotage.”

Others have been less restrained. Mehdi Mohammadi, an adviser to the parliament speaker, called Pickaxe Mountain “the most heavily fortified nuclear facility in the world” and said a strike would “turn the region into hell.”

Iran’s joint military command has warned that any attack on nuclear or sensitive sites would widen the war.

Every time Trump has threatened it

July 13. On the Hugh Hewitt show: “We have eyes on it and Pickaxe mountain is a possible target for a nice big fat shot right in the front door. We’re watching Pickaxe Mountain very closely. We don’t see any activity there.” He ended the interview more bluntly: “We’re going to take out Pickaxe Mountain. Tell the Iranians to be ready.”

July 21. After the Israeli intelligence assessment surfaced: “The new site that they’re talking about, they’re trying to possibly reconstitute a site, we’ll hit that site. Any site where they’re even thinking about nuclear, we’ll be hitting it very, very powerfully.” He said the US would hit the area “pretty soon, and very heavily.”

July 28. “I know exactly what’s going on at Pickaxe. It’s not a big problem. We took out their nuclear sites, and we’ll have to take out Pickaxe if we don’t make a deal.”

September 4. Trump said the US may hit the site very soon, crediting the Space Force for the intelligence. “We know everybody that’s moving at Pickaxe, we know everybody that’s moving everywhere, all over Iran, and if anything goes bad, we hit them. We hit them hard.” He called the conflict a “military conflict” rather than a war, and added: “It’s small potatoes for us.”

So why has it not been hit?

Across two wars, the only recorded strike at the site destroyed a single vehicle on a spoil pile, thought to have been connected to air defense.

One explanation is simply that it is hard to destroy and may not yet contain anything worth destroying.

Iran has spent the interval hardening it further: concrete poured over a western entrance extension, a reinforced structure added at another portal, rock and soil pushed up over an eastern one, and by late April both eastern entrances partially backfilled to block vehicles.

A separate, smaller tunnel complex inside the same perimeter, built in 2007, was sealed shortly after the June 2025 war. What is inside it is unknown.

The other explanation is that Washington wants the option of getting in rather than burying it. Rebeccah Heinrichs of the Hudson Institute has suggested the United States may be preserving the possibility of entering or securing the complex, which would mean a ground operation rather than an air strike. There is no public evidence that one is being planned.