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)