A hole in the rock is not just a hole in the rock. Grand Canyon National Park runs two entirely separate legal categories for the things underground — cave and mine — and which one applies decides who can get a permit, what the closure paperwork says, and whether the thing that killed the last person who wandered in was a rockfall or a fungus.

The short version

• Federal law defines “cave” as a naturally occurring void — and specifically excludes mines, tunnels, and other manmade excavations from that definition.
• Grand Canyon’s own management rules go further, requiring a natural opening to be at least 50 feet long and narrower than it is deep to count as a cave at all — which is why Redwall Cavern, a giant natural amphitheater every river trip stops at, officially isn’t one.
• “Mine” gets its own management definition: any human-made excavation for mineral extraction, covering everything from a hand-dug prospect pit to a 1,500-foot uranium shaft.
• Both categories are closed to the public by nearly identical rules — but for different stated reasons, safety and archaeology for mines, safety, archaeology, and biology for caves.
• Nobody has a precise count of either. NPS estimates the park may hold as many as 2,500 caves with several hundred documented (a more recent inventory effort puts documented caves over 660); no equivalent official total exists for mine features.
• The two categories overlap more than the rulebook suggests — abandoned mine shafts are now serious bat habitat, so a “mine” closure and a “cave” closure can end up protecting the same thing.

What actually separates a cave from a mine

The starting point is federal, not local. The Federal Cave Resource Protection Act of 1988 defines a cave as:

“Any naturally occurring void, cavity, recess, or system of interconnected passages which occurs beneath the surface of the earth or within a cliff or ledge (including any cave resource therein, but not including any vug, mine, tunnel, aqueduct, or other manmade excavation) and which is large enough to permit an individual to enter, whether or not the entrance is naturally formed or manmade.”

Read that middle clause again: the federal definition of “cave” explicitly carves mines back out. A hand-dug adit and a water-carved passage can look identical from the entrance, sit twenty feet apart in the same cliff face, and belong to two different legal universes.

Grand Canyon’s Superintendent’s Compendium — the park’s current rulebook, effective June 16, 2026 — adds a park-specific wrinkle on top of the federal definition: for management purposes, any dissolution or erosion feature counts as a cave only if it’s at least 50 feet long and its entrance is no wider than the feature is long. The compendium supplies its own counterexample: “Redwall Cavern is not a cave by definition” — the famous, room-sized overhang on the river corridor fails the test because its opening is wider than it is deep. It’s a natural feature, a genuinely spectacular one, and administratively not a cave at all.

“Mine” gets the opposite treatment — deliberately broad. The compendium defines it as “any anthropogenic feature excavated for the purpose of mineral extraction,” and spells out that this catches adits, shafts, pits, tunnels, prospects, and tailings piles alike. A single test hole scraped out by a prospector in 1891 who never found anything counts exactly the same as the Orphan Mine’s 1,500-foot uranium shaft. Origin of the hole, not its size or history, is what the definition turns on.

How the two get closed — and why the reasons differ

Once something is legally a mine or a cave, the closure language is almost a mirror image. All mines in the park are off-limits to the public except for people with written superintendent permission for research or administrative work, justified by “human health and safety, unrecorded features, archaeological resources, and wildlife habitat.” All caves require a valid entry permit, justified by protecting “the many unrecorded features, archaeological resources, and various life that may reside in the thousands of Grand Canyon caves.”

Read closely, the mine rule leads with safety — shafts collapse, ladders rot, old timber gives way — while the cave rule leads with biology and archaeology on top of the same safety concerns. That’s not boilerplate. Individual named sites get their own, more specific closures layered over the general rule. The Orphan Mine’s fence line cites “open shafts, sharp metal, and varying levels of radioactivity” — a hazard list that reads like a mine, because it is one. Cave of the Domes, by contrast, is closed specifically “to protect bats residing within the cave” and to stop humans from carrying in the fungus that causes white-nose syndrome — a biological rationale that has nothing to do with mining and everything to do with what lives there. Two named river-corridor caves get their own one-line bans layered on top of the general permit rule: Bat Cave and Rampart Cave. Rampart Cave’s closure has a specific history behind it — it held one of the most significant Shasta ground sloth dung deposits in North America, studied by Smithsonian researchers since the 1930s, until vandals broke its protective gate in 1976 and started a fire that burned through 70% of the deposit.

What the inventories actually say

Here’s where the record gets honestly thin. NPS’s own Geodiversity Atlas for the park states that almost all of Grand Canyon — 97% — sits on karst terrain, more than any National Park Service unit except the Everglades, with the Redwall Limestone hosting most of the caves. From that geology, the Atlas estimates the park “may contain as many as 2,500 caves with several hundred caves having been documented.” A more recent, narrower figure comes from ongoing NPS-permitted cave inventory fieldwork reported by Arizona Highways magazine in 2024: “the park has documented more than 660 caves.” Both numbers come from legitimate NPS-linked sourcing; they simply reflect different points in an inventory that is still actively growing. That growth is real and recent — a cave system found in 2007-2008 by permitted caver Jason Ballensky has since been mapped past 40 miles of passage, making it one of the longest known caves in the world, and it’s still not fully explored. It also holds a scientifically significant deposit of naturally mummified bats, a find covered in more depth in the bats and white-nose syndrome piece.

Nothing comparable exists on the mine side. The definitive published inventory — George Billingsley, Earle Spamer, and Dove Menkes’s 1997 monograph Quest for the Pillar of Gold: The Mines & Miners of the Grand Canyon — documents the canyon’s mining history site by site, but no total feature count from it turned up in this research. What the historical record does make clear is the shape of the mining era rather than its raw numbers: prospectors organized roughly nine mining districts in and around the canyon in the 1870s-80s, under rules that capped claims at 20 acres but placed no limit on how many claims one person could hold. Across about 40 years of that free-for-all, “hundreds of prospectors and dozens of miners worked tirelessly,” and by one careful historian’s count, fewer than half a dozen copper and asbestos mines plus a single uranium mine ever turned a real profit. The rest were often filed to tie up scenic real estate rather than to dig it — “many of them merely speculative and some downright bogus,” as Grand Canyon Historical Society’s account puts it. Nationally, NPS’s Abandoned Mineral Lands program has tallied roughly 38,000 hazardous mine features across the whole park system, but no park-specific figure for Grand Canyon was found this session — a genuine gap, not a rounding error.

Where mines and caves turn out to be the same problem

The two categories aren’t as separate in practice as the rulebook implies. Old mine workings across the National Park System have become de facto bat habitat: of the 45 bat species native to the U.S., 29 use mines for some part of their life cycle, and NPS’s own page on Grand Canyon bats says it plainly — “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.” That means closing a mine and closing a cave can serve the identical biological purpose. NPS’s toolkit for sealing hazardous mine openings — steel gates, cupolas, wire cable netting, earthen backfill — includes “bat gates,” designed to let bats fly freely in and out while keeping people out, and any closure work near bat habitat has to follow the same white-nose syndrome decontamination protocol used in caves (see bats, white-nose syndrome and cave closures).

What’s actually off-limits (and why)

In practice: every mine in the park and every cave in the park are both closed to casual visitors, full stop, under the compendium’s general rules — no exceptions for “just looking,” no informal access even to sites without a name or a fence. What differs is the stated reasoning layered on top for specific sites. Mines close because they’re dangerous and historically significant (the Orphan Mine is the clearest example). Caves close because they’re dangerous, archaeologically sensitive, and biologically irreplaceable — a distinction that matters most for the park’s bat population, covered in full in the companion piece on white-nose syndrome and cave closures. For the bigger picture connecting both categories to the park’s tunnels, shafts, and utility corridors, see Grand Canyon Underground; for the general framework behind every closure in the park, see What’s actually off-limits at the Grand Canyon, and why.

Sources

1. Grand Canyon National Park Superintendent's Compendium, effective June 16, 2026 — National Park Service
2. NPS Geodiversity Atlas — Grand Canyon National Park, Arizona — National Park Service
3. To the Batcave — Arizona Highways
4. Inside the Grand Canyon's Longest Known Cave — Grand Canyon Trust
5. Mining — Nature, Culture and History at the Grand Canyon (Grand Canyon Historical Society, by Michael F. Anderson)
6. Miners — Grand Canyon National Park (National Park Service)
7. Quest for the Pillar of Gold: The Mines & Miners of the Grand Canyon — Open Library / Grand Canyon Association Monograph No. 10
8. Abandoned Mineral Lands — National Park Service
9. Mines as Habitat — Abandoned Mineral Lands, National Park Service
10. AML Closures — Abandoned Mineral Lands, National Park Service
11. Bats — Grand Canyon National Park (National Park Service)
12. Pleistocene Life and Landscapes — Grand Canyon (National Park Service)