Grand Canyon holds the highest bat diversity of any unit in the National Park Service — 22 species, a dozen of which hibernate through winter in the park's caves and old mine shafts. That's exactly the biology a cold-loving fungus needs. It's been closing in on Arizona for years, and in 2025 it arrived.

The short version

• White-nose syndrome (WNS) is caused by Pseudogymnoascus destructans (Pd), a fungus that thrives in cold, humid hibernation sites and has killed millions of bats since it was first documented in New York in 2006.
• Grand Canyon has 22 documented bat species, 12 of them hibernating — the group WNS targets, because it infects bats while they’re too dormant to fight it off.
• A single low-level, inconclusive Pd detection turned up in a Grand Canyon bat in 2019. Confirmed disease has never been documented in the park.
• Arizona’s status changed in February 2025: state biologists confirmed high-level Pd on a bat with suspicious wing damage near Sierra Vista, and trace fungus has separately turned up in Coconino County — the county Grand Canyon sits in.
• Two of the park’s own web pages haven’t caught up to that news; one still says the fungus “has not reached Arizona.”
• The park’s response is the same tool used against mine hazards: close the cave, control what people carry in on their boots.

What white-nose syndrome actually is

Pseudogymnoascus destructans is a fungus that grows best in cold, damp places — which happens to describe the inside of a hibernation cave perfectly. It gets its common name from the fuzzy white growth it produces on an infected bat’s muzzle and wings. The fungus doesn’t kill bats directly so much as it disrupts them: infected bats rouse from hibernation more often than they should, burning through fat reserves meant to last the whole winter, and many starve or dehydrate before spring. It was first documented in a New York cave in February 2006 and has since reached 40 U.S. states and 9 Canadian provinces, killing millions of bats along the way. A 2021 USGS-led study covering 23 years of winter survey data found that three species — northern long-eared bat, little brown bat, and tri-colored bat — had each declined by more than 90% in the areas WNS had reached. The disease poses no risk to humans or pets, but people can carry its spores between caves on contaminated clothing, boots, and gear, which is exactly why cave-entry rules exist.

Grand Canyon’s exposure

Grand Canyon National Park has the highest bat diversity of any National Park Service unit: 22 documented species, ranging from the tiny canyon bat — usually the first one seen at dusk — up to larger species that roost in cliff cracks, ponderosa pine snags, old mine workings, and caves. Of those 22, 12 hibernate through the winter, which is the group WNS specifically targets, since the fungus needs a dormant host to do its damage.

The park has been watching for it since at least 2015, running acoustic surveys across an elevation gradient from the rim to the river and periodically capturing bats to check for signs of infection. In April 2019, a fringed myotis captured during routine surveillance tested “inconclusive” for Pd — a swab came back with trace levels too low to count as a confirmed detection under the standard case definition, and the bat showed no outward signs of disease. Follow-up sampling that June, and a review of the park’s samples from prior years, found nothing. Grand Canyon wildlife biologist Brandon Holton said at the time that the park would step up winter and spring surveillance, since that’s when infected bats are most likely to shed detectable fungus. The U.S. Fish and Wildlife Service’s national WNS coordinator noted that many western bat species hadn’t yet been exposed, and that Southwestern bats’ habit of hibernating alone or in small groups — rather than the dense colonies common in eastern caves — might slow transmission even after the fungus arrives. Might, not won’t.

2025: the fungus gets a foothold in Arizona

That changed, at least for the state as a whole, in February 2025. Arizona Game and Fish Department announced that a cave myotis sampled at Fort Huachuca near Sierra Vista, in the state’s southeast corner, had tested positive for Pd at a high enough level to be linked to visible wing abnormalities — the first Arizona detection tied to physical symptoms rather than a bare trace reading. Four other bats sampled in the same effort, across two more species, carried trace amounts. Fort Huachuca had been watching for the fungus since 2014 and running DNA sampling since 2017, with low-level flags in 2021 and 2023 before the 2024 sample (confirmed by lab results in early 2025) crossed into “concerning.”

The bigger picture, per the same release: since 2019, trace Pd has turned up during statewide surveillance in at least four Arizona counties — Mohave, Coconino, Yavapai, and Cochise — and between 2021 and 2024, eight bats total tested positive for trace fungus, spanning cave myotis, southwestern myotis, and big brown bats. Coconino County is where Grand Canyon National Park sits. That doesn’t mean the fungus has been found inside the park itself — the state’s county-level reporting doesn’t say where within the county each sample came from — but it means Grand Canyon is no longer somewhere-off-in-the-distance from a confirmed detection. It’s in the neighborhood. Arizona Game and Fish’s state bat specialist, Angie McIntire, put it plainly: “It’s concerning, but not surprising given how Pd has been spreading from state to state over the past several years.” Arizona public radio station KJZZ, reporting independently days later, noted there’s still no cure — prevention, meaning keeping people and their gear from moving spores between sites, is what wildlife agencies have to work with.

Two of the park’s own pages haven’t been updated to reflect that shift. Grand Canyon’s cave and karst page, last revised in May 2024, still tells visitors the disease “has not reached Arizona.” A separate NPS page describing the park’s bat research projects is dated all the way back to 2017 — before even the 2019 inconclusive detection. Neither is wrong about what it says for the date it was written; they’re simply behind the most current confirmed information, which is a useful reminder that a park website’s “last updated” stamp matters as much as its text.

Why the caves stay shut

Grand Canyon’s current Superintendent’s Compendium, effective June 16, 2026, closes Cave of the Domes to public entry except by written superintendent permission, and gives two reasons in the same sentence: stopping people from disturbing roosting and hibernating bats, and stopping people from carrying Pd into the cave on their gear. That’s a closure built specifically around this disease, not a generic safety rule borrowed from elsewhere in the rulebook. Two more named caves along the river corridor, Bat Cave and Rampart Cave, are separately closed to any entry under the same compendium — full stop, no permit process at all for the public.

Rampart Cave’s closure has history behind it that has nothing to do with bats and everything to do with why NPS takes vandalism in these places seriously. The cave held one of North America’s most significant Shasta ground sloth dung deposits — several feet thick in spots, with layers dating from before 40,000 years ago to roughly 11,000 years before present. NPS specialists first investigated in 1936; the Smithsonian Institution ran the largest excavation in 1942. In 1976, despite a protective gate, vandals broke in and started a fire that destroyed 70% of the deposit. It’s the kind of loss that doesn’t come back, and it’s part of why “closed” at Grand Canyon tends to mean closed, not “ask a ranger nicely.”

Mines, caves, and the same bats

The park’s cave closures don’t operate in isolation from its mine closures — biologically, they’re often protecting the exact same animals. Nationally, 29 of the 45 bat species native to the United States rely on abandoned mines for some part of their life cycle: summer roosts, winter hibernation, nurseries, or stopovers during migration. Grand Canyon’s own bat page states the overlap directly: “Before the Grand Canyon was a National Park, it was home to many copper, gold, and uranium mines. Now these abandoned mines make excellent habitat for many bat species.” NPS’s toolkit for sealing hazardous mine openings across the park system includes wildlife-accessible “bat gates” and cupolas — steel structures that let bats fly freely in and out while keeping people from wandering into a collapsing shaft — and any closure work done in or near bat habitat is required to follow the same White-Nose Syndrome decontamination protocol used at cave sites. A “mine” closure sign and a “cave” closure sign can be protecting the identical colony (see mines versus natural caves for how the park draws that legal line in the first place).

What’s actually off-limits (and why)

Cave of the Domes: closed to the public except by written superintendent permission, specifically to protect roosting and hibernating bats and to prevent people from carrying Pd inside. Bat Cave and Rampart Cave: closed to entry entirely under the park’s river-corridor rules, no permit process. All three sit inside the park’s broader rule that every cave requires an entry permit and every mine is closed except for authorized research or administrative work — see mines versus natural caves for that general framework, and Grand Canyon Underground for how it connects to the park’s tunnels and shafts. None of this is about keeping people from a pretty hole in the rock. It’s about a fungus that’s already most of the way to the park’s front door.

Sources

1. Mines as Habitat — Abandoned Mineral Lands, National Park Service
2. Bats test positive for possible deadly fungus — Arizona Game & Fish Department
3. Bats — Grand Canyon National Park (National Park Service)
4. White-Nose Syndrome Killed Over 90% of Three North American Bat Species — U.S. Geological Survey
5. Fungus That Causes White-Nose Syndrome Possibly Detected At Grand Canyon National Park — National Parks Traveler (reproducing NPS news release)
6. White nose syndrome that has decimated millions of bats confirmed in Arizona — KJZZ
7. Cave / Karst Systems — Grand Canyon National Park (National Park Service)
8. Bat Projects in Parks: Grand Canyon National Park (National Park Service)
9. Grand Canyon National Park Superintendent's Compendium, effective June 16, 2026 — National Park Service
10. Pleistocene Life and Landscapes — Grand Canyon (National Park Service)
11. AML Closures — Abandoned Mineral Lands, National Park Service

For most of the last century, Cave of the Domes was the one hole in the ground at Grand Canyon you could walk into without asking anyone's permission. It survived a copper bust, a hantavirus scare, and decades of mule-tour tourism. Bats are what finally closed it.

The short version

• Cave of the Domes sits at the end of the Grandview Trail on Horseshoe Mesa, next to the old Last Chance copper mine that first brought tourists down there in the 1890s.
• It was, for decades, the single named exception to Grand Canyon’s blanket cave-permit rule — the only cave in the park you could enter without written NPS authorization.
• In March 2016 it was briefly closed over a hantavirus scare tied to rodent activity, then reopened two months later once NPS ruled it out as the exposure source.
• As late as December 2019, NPS was still describing it as “the one cave in Grand Canyon National Park open to the public.”
• Sometime after that — the exact date isn’t nailed down in what NPS currently publishes — the open-access exception ended. The current Superintendent’s Compendium closes it outright, citing bat protection.
• The reason is white-nose syndrome: a fungal disease that has wiped out bat colonies across the country, and that human foot traffic and gear can carry from cave to cave.

A copper mine’s tourist trail

Cave of the Domes doesn’t have its own origin story in the record — it shares one with Horseshoe Mesa. In 1893, Pete Berry and partners Niles Cameron, Ralph Cameron, and Ed Gale staked the Last Chance copper claim on the mesa, at the end of what’s now the Grandview Trail. The ore was good enough to win a purity prize at Chicago’s 1893 World’s Fair, and the operation ran for fourteen years, with mule trains hauling roughly 200 pounds of ore up the trail per animal per trip and carrying food and supplies back down — enough copper, over the mine’s life, to fill 140 railroad cars.

Berry didn’t just mine the mesa; he sold it. He personally led tourist excursions down the Grandview Trail to Horseshoe Mesa, sometimes all the way to the Colorado River, well before Grand Canyon was even a national park. That’s the same access route, and roughly the same era, that put Cave of the Domes on the map as a walk-in attraction rather than a technical caving destination. Copper prices collapsed in 1907 and the mine shut down, but the trail — and the cave at the end of it — kept drawing visitors long after the miners left.

The one cave you didn’t need a permit for

Grand Canyon has treated caves as off-limits by default for a very long time. The park’s 1988 Backcountry Management Plan states it plainly: “Cave use and management is guided by the park’s Cave Management Plan. All caving activity (day use or overnight), except for access to Cave-of-the-Domes on Horseshoe Mesa, must be approved in advance through the Resources Management and Planning Division.” That sentence held for decades. A 2016 Williams-Grand Canyon News report on the cave repeats the same structure almost word for word: “Cave of the Domes… is the only cave open to the public in [Grand Canyon National Park]. Old mines located near Horseshoe Mesa and throughout the park are also closed. With the exception of Cave of the Domes, permits are required to enter caves in [the park] because of the extremely sensitive nature of cultural and natural resources inside.”

Every other cave in the park — and there are thousands of candidate openings in the Redwall and Muav limestone alone — required a written permit. Cave of the Domes didn’t. You hiked the 3-mile Grandview Trail down to Horseshoe Mesa and walked in.

A hantavirus scare, then a longer closure

The first real interruption to that open-door policy came in March 2016, and it wasn’t about caving at all. Coconino County had logged two cases of Hantavirus Pulmonary Syndrome (HPS) that year, a rare but serious disease people can catch from rodent droppings, urine, or saliva. NPS temporarily closed Cave of the Domes “because of rodent activity and the potential for exposure to HPS,” effective March 23, 2016, “until further notice.” Two months later, NPS’s Office of Public Health cleared the cave — determined it wasn’t the exposure source — and reopened it.

That episode is well documented because it made local news twice, coming and going. What happened next is harder to pin down. As of December 2019, National Parks Traveler was still quoting Grand Canyon’s own materials describing Cave of the Domes as “the one cave in Grand Canyon National Park open to the public” — in an article about a different threat entirely: a possible detection of the fungus behind white-nose syndrome on a single bat. At some point after that, the open-access status ended. NPS’s current cave-resources page states flatly that “under the current park policy, all caves are currently closed to visitation, except for research purposes” — with no exception named for Cave of the Domes, and no date attached to when that changed. The two NPS news pages that would presumably document the transition — one titled as a closure notice, one as a status update — both return “page not found” as of this writing. Whatever the exact date, the record is consistent on the reason.

Why bats ended it

Grand Canyon is home to 22 bat species, and 12 of them hibernate — which makes them the ones at risk from white-nose syndrome, a disease caused by the fungus Pseudogymnoascus destructans. First identified in a New York cave in 2006, it has since been confirmed in 28 U.S. states and 5 Canadian provinces, and it kills by rousing hibernating bats more often than normal, burning through the fat reserves they need to survive winter. It doesn’t infect people; it spreads bat-to-bat and on contaminated gear, boots, and clothing carried between caves by cavers, researchers, and tourists.

Grand Canyon runs an active surveillance program to catch it early: eleven acoustic-monitoring stations spanning rim to river, seasonal mist-net captures, and roost surveys. In April 2019, park biologists got an inconclusive trace of the fungus on a single fringed myotis — not a confirmed detection, and not signs of the disease itself, but enough to sharpen the park’s caution. Grand Canyon Wildlife Biologist Brandon Holton put the stakes simply at the time: “Collecting samples in winter and spring increases the likelihood of detecting Pd and WNS, as bats are infected during hibernation over winter and shed the fungus shortly after emergence in the spring.” NPS’s general playbook for protecting bats — laid out on its cave-resources page — includes visitor education, screening people and gear before they enter sensitive caves, disinfection protocols, and, “when necessary, closure of caves used by bats.” Cave of the Domes was, eventually, one of those closures.

What’s actually off-limits (and why)

The current Grand Canyon Superintendent’s Compendium (effective June 16, 2026) is unambiguous: “Cave of The Domes is closed to public presence, use, and access except with prior written permission from the park’s superintendent,” under 36 CFR § 1.5(a)(2). The park’s own stated reason is bat protection on two fronts — “stopping human disturbance of roosting and hibernating bats that reside within the cave” and “stopping human transmission of Pseudogymnoascus destructans, the causative fungal agent of White Nose Syndrome, to bats within the cave.”

That closure sits inside a broader park-wide rule: under compendium item 54, public presence, use, and access in all caves in Grand Canyon — as defined by the Federal Cave Resources Protection Act — is prohibited without a superintendent-authorized permit, “necessary to protect the many unrecorded features, archaeological resources, and various life that may reside in the thousands of Grand Canyon caves.” Cave of the Domes used to be the single carve-out from that rule. It no longer is. The trail to Horseshoe Mesa is still open to hikers; the cave at the end of it, for now, isn’t.

Sources

1. Grand Canyon National Park Superintendent's Compendium, effective June 16, 2026 — National Park Service
2. Backcountry Management Plan, September 1988 — Grand Canyon National Park, National Park Service
3. Cave / Karst Systems — Grand Canyon National Park, National Park Service
4. Current Bat Research — Grand Canyon National Park, National Park Service
5. Fungus That Causes White-Nose Syndrome Possibly Detected At Grand Canyon National Park — National Parks Traveler
6. Grand Canyon's Cave of the Domes closed for potential Hantavirus exposure — Williams-Grand Canyon News
7. Cave of the Domes Reopens in Grand Canyon — Williams-Grand Canyon News
8. Grand Canyon park officials close popular cave over hantavirus concerns — Fox News
9. Last Chance Mine — Nature, Culture and History at the Grand Canyon (Grand Canyon Historical Society)

The Grand Canyon's underground record is not a single lost chamber. It is thousands of caves and shelters, long surveyed systems, fossils that preserve old ecosystems, and caves that still shelter bats. The interesting part is what researchers can actually measure—and how easily a map or a number goes out of date.

The short version

• An NPS inventory identified 28 caves with fossil resources in 1998–2001. That is not a count of every cave in the park.
• Rampart Cave preserved fossil dung from two widely separated periods. A 1976 fire destroyed about 70% of the deposits.
• Stanton’s Cave has fossils and split-twig figurines. A reexamined fox specimen shows why museum collections can still produce new findings.
• In a 2012 NPS article, Leandras Cave was described as Arizona’s longest. A 2024 study reports a much longer mapped system, Double Bopper; the 2012 ranking is historical, not current.
• Bat Cave’s guano feeds a documented invertebrate community, while dated bat remains from two other caves extend from modern times to more than 45,800 calibrated years before present.
• These are protected research sites, not do-it-yourself destinations. The park’s published rules identify specific caves where public entry is prohibited.

An inventory is not a census

The canyon cuts across beds of Muav and Redwall limestone. An NPS paleontology inventory describes thousands of caves and shelters in those rocks. Its researchers identified 28 Grand Canyon caves containing paleontological resources in an inventory conducted from 1998 to 2001. Read that carefully: 28 fossil-bearing caves identified by that inventory, not 28 caves in the whole park. The inventory also extrapolated roughly 2,215 obvious Redwall openings in the eastern canyon from counts in three sampled areas and mapped outcrop length. That is a model estimate, not a ground-truthed address book.

Even the word “system” needs care. A cave might be a short shelter, a long network surveyed passage by passage, a biological refuge, an archaeological site—or several of those at once. A tally of entrances is not a tally of connected passage, and a mapped length is only as current as the last survey. The older inventory gives a good starting scale for the problem, not a final number to print on a souvenir magnet.

What the fossils say

Rampart Cave is the clearest demonstration of how much information dry cave floors can hold. NPS traces the earliest report of Grand Canyon cave fossils to 1936, at Rampart Cave. Subsequent work studied the dung deposit. NPS describes dung accumulating in one interval from before roughly 40,000 years ago to about 24,000 years before present, and again around 13,000–11,000 years before present. Those intervals are not one tidy layer of one tidy afternoon.

The archive was damaged, too. NPS says the cave was broken into in 1976 and a fire destroyed about 70% of the dung deposit. That is an account of the breach and loss, not evidence for assigning the fire to a particular person. The same NPS article says there does not appear to be evidence of human occupation at Rampart. An Ice Age animal shelter is already an impressive story; it does not need to become an imaginary ancient city. For that separate claim, see the Kincaid cave myth.

Stanton’s Cave is a different sort of layered record. The NPS inventory describes an archaeological site with split-twig figurines. NPS describes the figurines generally as made from a single twig, dating from about 2,000 to 4,000 years ago. The park says their precise function remains uncertain. That uncertainty matters; this is an archaeological record, not a prompt to invent a ceremony on somebody else’s behalf.

Work on a collection from Stanton’s Cave produced a more recent correction. A 2025 paper reexamined two fossil fox jaw fragments once reported as gray fox and identified them as red fox instead—the first such record reported from Grand Canyon. They also explicitly warn that the jaws have not been directly radiometrically dated. The find documents an identification; it does not pin down exactly when that animal lived.

The map kept growing

In a 2012 Park Science account of the Leandras Cave survey: by the final 2009 expedition, teams had mapped 42,329 feet, a little over eight miles. The article then called it the longest cave in Arizona. Surveying reportedly took roughly 700 hours underground, with another 500 hours to turn measurements and sketches into a usable map.

Research moved on. A peer-reviewed 2024 Parks Stewardship Forum study gives 24 kilometers (15 miles) for Leandras in its abstract and 66 kilometers (41 miles) of known passage for Double Bopper Cave. The study says Double Bopper mapping was continuing. The Leandras figure in that study’s body is phrased more loosely as “more than 15 km”; neither version makes the 2012 length the last word. If you see a web page calling Leandras the state’s longest on the strength of the old NPS article, you are seeing a timestamp, not a live leaderboard. No newer survey was verified here, so even the 2024 lengths are stated as 2024 findings, not September 2026 totals.

Living caves, not just fossil cupboards

Bat Cave shows the biological side. In four expeditions between 1994 and 2001, entomologist Robert Pape documented 27 taxa there, including 22 macro-invertebrate species. A beetle first described from the cave is part of that record. The cave’s bats supply guano, supporting the invertebrate food web. There is also an industrial footnote: a guano venture begun in 1958 reportedly invested $3.5 million, then found the deposit was only about one percent of the original estimate and abandoned mining by 1960. The creatures did a better job maintaining an economy than the company.

Leandras and Double Bopper supplied another question: are the many dried bat remains evidence of one disaster or long use over time? The 2024 researchers inventoried 482 bat specimens from the two caves, representing at least 12 species. Their 67 radiocarbon samples ranged from modern to more than 45,800 calibrated years before present. The dominant species differed between the caves: silver-haired bats at Leandras and Townsend’s big-eared bats at Double Bopper. That spread argues against one single die-off explaining everything. It does not mean every year in between was sampled or prove uninterrupted use.

What’s actually off-limits (and why)

In 2012, the park’s cave manager wrote that Grand Canyon caves were closed to ordinary visitation for safety and preservation, with some entries or surveys possible under cave-entry or research permits. The Superintendent’s Compendium effective June 16, 2026, checked for this page as of September 23, 2026, separately prohibits entry into Bat Cave and Rampart Cave. It closes Cave of the Domes to public presence, use and access except with prior written permission. For that cave the compendium specifically cites disturbance of roosting or hibernating bats and the risk of introducing the fungus that causes white-nose syndrome.

Those published restrictions are enough to explain the absence of visitor directions here. This page gives no cave coordinates, river miles, entrance descriptions or access routes, and it does not turn protected sites into a checklist. The interesting underground infrastructure is the scientific record: layers, measurements, permits, and careful curation.

Sources

1. An Inventory of Paleontological Resources Associated with Caves in Grand Canyon National Park — National Park Service researchers
2. Pleistocene Life and Landscapes—Grand Canyon — National Park Service
3. Archaeological Resources — Grand Canyon National Park
4. Red Fox Remains from Stanton's Cave (2025) — Journal of Cave and Karst Studies
5. Hidden Wonder: The Discovery and Survey of Leandras Cave (2012) — NPS Park Science
6. Ancient Bat Remains Illustrate the Role of Caves as Habitat Anchors (2024) — Parks Stewardship Forum
7. Biology and Ecology of Bat Cave (2014) — Journal of Cave and Karst Studies
8. Grand Canyon National Park Superintendent's Compendium (effective June 16, 2026) — National Park Service

Ninety-seven percent of Grand Canyon National Park sits on karst — rock that dissolves into caves. Some of those caves, over millions of years, collapsed and filled with ore, and people spent a century digging the ore back out. Caves and mines aren't two unrelated stories at Grand Canyon. Often they're the same hole, at two different points in its life.

The short version

• Almost all of Grand Canyon’s bedrock is karst, and the Redwall Limestone that hosts most of its caves is the same formation that hosts its uranium deposits — the two aren’t a coincidence of geography, they’re a shared origin.
• “Breccia pipes,” the vertical ore columns miners chased for a century, form when ancient caverns in that limestone collapse and later fill with metal-bearing groundwater. A uranium mine and a fossil cave can be the same feature at different points in its history.
• NPS estimates the park holds as many as 2,500 natural caves (several hundred formally documented, a more recent inventory puts it past 660) and, on the mining side, has counted 38 abandoned-mine sites with 75 individual features.
• Federal and park rules treat “cave” and “mine” as legally separate categories with separate closure justifications — but the same bats often live in both, which is where the rulebook and the biology reconnect.
• The park’s single most-studied cave system, found in 2008, has been mapped past 40 miles of passage and holds thousands of naturally mummified bats up to 50,000 years old — a scientific trove that has nothing to do with either mining or white-nose syndrome.

The shared geology nobody mentions on the rim trail

Start with the rock. Almost the entire park — 97% — sits on karst terrain, limestone and related rock riddled with the voids that water carves out over geologic time; another 3% is pseudokarst, similar-looking terrain formed by other processes. Only Everglades National Park has more karst area than Grand Canyon among all National Park Service units, and here it’s concentrated in one formation: the Redwall Limestone, the reddish-gray band about a third of the way down the canyon wall that hosts the majority of the park’s caves.

That same limestone is also where the canyon’s mining history comes from. “Breccia pipes” — the vertical, cylindrical ore bodies that produced nearly every uranium mine in and around the canyon — form when caverns inside the Redwall Limestone collapse under the weight of overlying rock, leaving a rubble-filled chimney that groundwater later saturates with dissolved metals, chiefly uranium and copper. It’s an unusual geologic mechanism, common in this part of northern Arizona and southern Utah and rare almost everywhere else; it’s also generous enough to have produced at least one mineral, grandviewite, found nowhere on Earth outside Grand Canyon. Put plainly: a breccia-pipe uranium mine isn’t built near an old cave. Structurally, it’s built inside one — a cave that collapsed, filled with ore, and got excavated a second time by people instead of water. The Orphan Mine, which pulled roughly 495,000 tons of ore and 4.26 million pounds of uranium oxide out of the South Rim between 1956 and 1969, is the best-documented example of this exact process.

Two different ways of counting holes

Ask NPS how many caves are in the park and you get an estimate with real uncertainty attached: as many as 2,500, with several hundred formally documented by the park’s Geodiversity Atlas, and a more recent, narrower figure from ongoing NPS-permitted survey work putting the documented count past 660. Ask about mines and you get something closer to an actual tally: 38 documented Abandoned Mineral Lands sites containing 75 individual features — adits, shafts, pits, tunnels, prospects, and tailings piles — with 12 of those 38 sites flagged as needing active mitigation. Those hazards run the range you’d expect from a century of hand-dug and machine-bored excavation: high radon, radioactive soils, asbestos, unstable debris, slope failure, and subsidence.

The two counts aren’t measuring the same thing the same way, and shouldn’t be added together. Caves are counted by exploration — someone has to physically find and survey a passage before it’s “documented,” and most of the park’s caves sit on cliff faces nobody has reason to visit. Mines are counted by federal environmental-liability inventory, a very different and more systematic process, because the government is legally obligated to track hazards on its own land. That gap in methodology is itself a small piece of the underground story: nature’s inventory is still being written by cavers with headlamps; industry’s inventory was closed out by federal accountants. For the full breakdown of what those 75 mine features are and where the money to close them has gone, see the mine inventory.

Same rock, different rulebook

Legally, the two categories don’t overlap at all. The Federal Cave Resource Protection Act of 1988 defines “cave” as a naturally occurring void and explicitly excludes “any vug, mine, tunnel, aqueduct, or other manmade excavation.” Grand Canyon’s current Superintendent’s Compendium, effective June 16, 2026, sharpens that further for management purposes — a natural opening only counts as a cave if it’s at least 50 feet long with an entrance no wider than it is deep — while defining “mine,” on the other side, as broadly as possible: any anthropogenic feature dug for mineral extraction, from a single 1890s prospect pit to a 1,500-foot uranium shaft. Both categories end up closed to the public by nearly parallel rules — mines need written superintendent permission for research or administrative work, caves need a valid entry permit — but for different stated reasons. Mine closures lead with safety. Cave closures lead with safety plus archaeology plus biology. For the full legal mechanics of that split, including why Redwall Cavern (a genuinely enormous natural feature on the river) technically fails the park’s own cave definition, see mines versus natural caves.

Where the rulebook’s clean split breaks down is biology. Nationally, 29 of the 45 bat species native to the U.S. rely on abandoned mines for some part of their life cycle — summer roosts, hibernation, nurseries — and Grand Canyon’s own mines are no exception; NPS says plainly that its abandoned copper, gold, and uranium workings “now make excellent habitat for many bat species.” That means a mine sealed for public safety and a cave sealed under Cave of the Domes’s bat-specific closure can be protecting the exact same colony, just under two different sections of the compendium. White-nose syndrome, the fungal disease that has killed millions of bats nationally since 2006 and was confirmed in Arizona for the first time in February 2025 — including trace detections in Coconino County, where the park itself sits — is the reason both categories now share the same decontamination protocol for anyone doing closure work near a roost.

The one cave nobody needed a mining company to find

Not every hole in this canyon has an industrial backstory, and the park’s best example proves it. In 2007-2008, caver Jason Ballensky located a cave system with no mining connection whatsoever — a purely natural discovery that has since been mapped past 40 miles of interconnected passage, ranking it among the longest known caves in the world, and it’s still not fully explored. Its location is kept undisclosed by NPS, and for good reason: the cave preserves hundreds, possibly thousands, of naturally mummified bats spanning at least 11 species, radiocarbon-dated from roughly 3,700 years old to beyond the ~50,000-year limit of the dating method itself, alongside preserved ringtails, foxes, raccoons, and rare gypsum-flower mineral formations. It’s a paleontological deposit, not a modern die-off — unrelated to white-nose syndrome — and it’s arguably the single best argument that this canyon’s underground is worth protecting on its own terms, independent of whatever was once mined out of it.

It’s also worth saying what this canyon’s underground definitely isn’t: there’s no lost Egyptian city, no hidden ancient civilization’s tunnel network, whatever a century-old newspaper hoax might still claim. See the Kincaid/Egyptian cave myth for how that story got started and why the geography it describes doesn’t hold up.

What’s actually off-limits (and why)

Every documented cave and every documented mine in Grand Canyon National Park is closed to casual public entry — full stop — under the compendium’s general rules, with individually named sites (Orphan Mine, Cave of the Domes, Bat Cave, Rampart Cave) carrying their own specific closure language on top. Cave management and permitted access are their own detailed topic; so is the park’s broader catalog of known, researched cave systems. For the general framework behind every closure in the park, not just underground ones, see what’s actually off-limits at the Grand Canyon, and why.

Sources

1. NPS Geodiversity Atlas — Grand Canyon National Park, Arizona — National Park Service
2. Inside the Grand Canyon's Longest Known Cave — Grand Canyon Trust
3. Grand Canyon National Park Superintendent's Compendium, effective June 16, 2026 — National Park Service
4. Science for Decision Making on Uranium Mining in Arizona: Orphan Mine — U.S. Geological Survey
5. Bats test positive for possible deadly fungus — Arizona Game & Fish Department
6. Mines as Habitat — Abandoned Mineral Lands, National Park Service
7. To the Batcave — Arizona Highways