Rockhounding at Spencer Opal Mines, Idaho
ALLOWED
No permit required
Key Conditions
- Spencer Opal Mines' tailings-pile dig — $75 per adult, $50 per child under 16 — sits entirely on privately claimed, patented ground; you pay the operator's fee directly, no government permit or reservation is needed
- No clearly mapped, publicly accessible BLM opal-bearing parcel comparable to the commercial claim was confirmed for this page — BLM's standard casual-collecting allowance applies to genuinely open public land in the surrounding district, but that's a different, unmapped proposition from where most visitors actually dig
- Spencer opal carries the same hydrophane risk documented at volcanic opal deposits nationally — rough stone can lose water content and crack ("craze") if it dries too fast after coming out of the ground
- The operation is strictly seasonal, roughly Memorial Day weekend through mid-September, and weather-dependent even within that window
- Vertebrate fossils, archaeological material, and anything inside an active mining claim boundary are off-limits regardless of where you are in the district
Spencer Opal Mines at a Glance
No
Government permit required?
$75 / $50
Fee (adult / child)
No
Reservation needed?
~Memorial Day–mid-Sept
Season
31
Town population (2020)
Almost No One Here Is Actually Digging on Public Land
The productive opal ground around Spencer, including the mine that supplies the commercial tailings pile, sits on a patented private mining claim — deeded land, not BLM public domain. That's the ground nearly every visitor actually digs, for a flat operator's fee, with no government permit involved. If you're picturing a free BLM casual-collecting trip instead, no specific, clearly mapped, publicly accessible opal-bearing parcel near Spencer was confirmed for this page. Don't assume unclaimed-looking ground near the commercial operation is open to you.
- $75 per adult, $50 per child under 16 for tailings-pile digging
- No reservation required — walk-up digging any day the shop is open
- Closed-toe shoes required; eye protection required while digging
- Fresh ore brought down to the pile weekly
- Seasonal operation, roughly Memorial Day weekend through mid-September
Source: Spencer Opal Mines, 27 Opal Ave, Spencer, ID 83446, 208-374-5476
The opal at Spencer formed through hydrothermal activity roughly 4 million years ago, when silica-rich water from geyser activity moved through a rhyolite-obsidian volcanic flow riddled with gas-pocket cavities, depositing thin, high-quality opal layers inside those voids. That geologic process is why the material here is prized for its transparency and vivid play-of-color rather than for size — the opal fills small cavities in volcanic rock, not the larger veins you'd find in a sedimentary deposit.
The deposit's discovery story is one of the more consistently repeated pieces of Idaho rockhounding lore: hunters caught out by a storm sat down to wait it out and noticed opalized rock nearby. Regional sources disagree on exactly when this happened — accounts place it anywhere from the late 1940s to the early 1960s — but every version agrees on the basic shape of the story, and on the fact that Spencer remains the only opal mine in Idaho still producing gem-quality material today.
Hydrophane Opal: Why Your Find Might Crack After You Get It Home
Opal from volcanic deposits like Spencer's can be hydrophane — porous enough to absorb and hold a significant amount of water, sometimes reported as high as 20% of the stone's weight. That water content is part of what gives the material its play-of-color while it's still damp from the ground. If a rough stone dries out too quickly — left in a hot car, a dry display case, or direct sun — the loss of internal water can cause cracking, known in the gem trade as crazing. Keep freshly dug material damp and let it dry slowly over days or weeks rather than trying to speed up the process.
Spencer Opal Mines vs. Surrounding Public Land
| Access Type | Government Permit? | Cost | Daily Limit | Land Status |
|---|---|---|---|---|
| Spencer Opal Mines tailings pile | No | $75 adult / $50 child | None stated — bucket-based | Private, patented claim |
| Surrounding BLM public land (where genuinely open) | No | Free | 25 lbs/day + 1 piece, 250 lbs/yr (43 CFR 3622.2) | Federal, subject to unmapped claim overlap |
Verified against Spencer Opal Mines' official site and BLM casual-collecting regulations, August 2026. Confirm any specific parcel's status with the Upper Snake Field Office before assuming it's open.
Getting There
Verified against Spencer Opal Mines' official site, August 2026.
When to Go
Late spring (Memorial Day–Jun)
GoodSeason opening; call ahead since exact opening date is weather-dependent at this elevation (nearly 6,000 ft).
Summer (Jul–Aug)
GoodPeak season, most reliable hours and full ore supply on the tailings pile; also peak Yellowstone-area tourist traffic passing through on I-15.
Early fall (Sep)
FairOperation typically winds down by mid-September — confirm current closing date before planning a trip this late in the season.
Winter (Oct–Apr)
ClosedClosed for the season. High elevation and I-15 mountain-pass conditions near Monida Pass make this an impractical time to visit regardless of shop status.
Recommended Gear
- RequiredClosed-toe shoes— Required at the tailings-pile dig site.
- RequiredEye protection— Required while digging; confirm whether it's provided on-site or bring your own.
- OptionalSmall rock hammer or chisel— Useful for breaking down larger rhyolite chunks pulled from the pile.
- OptionalDamp cloth or sealed container— For transporting rough opal home without it drying out too fast.
Before You Go
- Call ahead to confirm the operation is open for the season and check current hours
- Bring closed-toe shoes and eye protection
- Fuel up and pack supplies before arriving — services in Spencer itself are minimal
- Bring a way to keep rough opal damp for the trip home
- Don't plan to dig outside the designated tailings-pile area without confirming land status first
Permits & Licenses
| Permit | Required? | Notes |
|---|---|---|
| Spencer Opal Mines tailings-pile dig | No | No government permit needed — this is a private operator's fee, paid on-site. No reservation is required; fresh ore is brought down to the pile weekly. |
| BLM casual collecting (surrounding public land) | No | Standard 43 CFR 3622.2 allowance (25 lbs/day plus one piece, up to 250 lbs/year) applies to genuinely open BLM ground. Confirm exact parcel boundaries with the Upper Snake Field Office before digging outside the commercial claim — the district is a patchwork of claimed and open ground that isn't obvious from the road. |
Time & Seasonal Restrictions
- Hand tools only anywhere in the area — no explosives, bulldozers, or motorized heavy equipment
- Vertebrate fossils and archaeological items are off-limits regardless of location
- Material inside any active or patented mining claim requires the claim holder's permission — most of the historically productive opal ground in the district falls into this category
- Open-toed shoes not allowed at the tailings pile; eye protection required at all times while digging
- The operation closes for the season by roughly mid-September — call ahead during shoulder-season months rather than assuming it's open
Equipment Notes
- 2.5-gallon bucket, included with the tailings-pile fee — no need to bring your own to start
- Closed-toe shoes, required at the dig site
- Eye protection, required while digging
- Small rock hammer or chisel, optional, useful for breaking down larger rhyolite chunks pulled from the pile
- A damp cloth or sealed bag for transporting rough opal, given the hydrophane cracking risk
What People Find Here
- Common opal (potch) in rhyolite — the most frequent tailings-pile yield
- Precious opal with play-of-color — less common, but the reason this deposit has drawn diggers continuously since its discovery decades ago
- Rhyolite and obsidian specimens from the host volcanic flow itself, alongside the opal material
Penalties for Violations
← Scroll to see all columns
| Violation | Statute | Penalty |
|---|---|---|
| Exceeding BLM's 25 lb/day plus 250 lb/year casual-collecting limit on genuinely open public land | 43 CFR § 3622.2 | Material collected beyond the limit may be treated as unauthorized removal of federal mineral material; citation possible |
| Digging within an active or patented mining claim without the claim holder's permission | General Mining Law of 1872 claim-rights framework | Trespass; potential civil liability to the claim holder |
Etiquette & Leave No Trace
- Confirm current fee, hours, and season status directly with Spencer Opal Mines before a long drive — this is a remote, strictly seasonal operation
- Keep rough opal slightly damp during transport home to reduce cracking risk
- Don't assume ground outside the commercial claim is open BLM land just because it looks similar — claim boundaries in this district aren't marked in a way a visitor can identify
- Respect the extremely small scale of the town itself (population 31 as of the 2020 census) — services are limited and this isn't a stop for last-minute supplies
- Report to on-site staff before attempting to dig outside the designated tailings-pile area
Frequently Asked Questions
Do I need a permit to dig at Spencer Opal Mines?
No government permit is needed. The tailings-pile dig is entirely on privately claimed land, and you pay the operator's fee — $75 per adult, $50 per child under 16 — directly, with no reservation required.
Is there free BLM land near Spencer where I can find opal on my own?
This isn't clearly resolved. BLM's standard casual-collecting rule applies to genuinely open public land managed by the Upper Snake Field Office in the surrounding district, but no specific, mapped, publicly accessible opal-bearing parcel comparable to the commercial claim was confirmed for this page. Most of the historically productive ground is claimed, not open. Confirm current parcel status with the field office before assuming you can dig for free nearby.
Why does my opal keep cracking after I get it home?
Spencer opal shares the hydrophane property documented at other volcanic opal deposits — it can hold significant water content, and rapid drying causes internal stress that cracks the stone, a process gemologists call crazing. Keep rough material damp and let it dry slowly and gradually rather than leaving it in a hot car or dry room right after digging.
When is Spencer Opal Mines open?
Seasonally, roughly Memorial Day weekend through mid-September, weather permitting. The shop generally runs Thursday through Monday, 9 a.m.–6 p.m., with tailings-pile digging available 9 a.m.–5 p.m. any day the shop is open. Call ahead in shoulder-season months to confirm current status.
How far is Spencer from Yellowstone National Park?
Roughly 70 miles. The town sits on I-15 near Monida Pass at the Idaho–Montana border, which puts it within reasonable day-trip range for visitors already in the Yellowstone area.
Who discovered the Spencer opal deposit?
Multiple regional accounts describe the same basic story — hunters caught in a storm noticed opal in the exposed rock and stopped to investigate — but sources disagree on the exact date, with some placing it in the late 1940s and others in the early 1960s. This page doesn't pick one over the other without a primary source confirming it.
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Disclaimer
Information is provided for general guidance only. Regulations change frequently. Always verify current rules with the official jurisdiction before relying on this information for legal decisions. Permitted Pursuits is not a substitute for official agency guidance. Report an error.
Sources
- Spencer Opal Mines — About Us(accessed 2026-08-28)
- BLM Upper Snake Field Office(accessed 2026-08-28)
- Gemmological Properties of Opals from Spencer, Idaho, USA — Minerals (MDPI)(accessed 2026-08-28)
Last verified: 2026-08-28 · Last updated: 2026-08-28