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Conjecture Mine: Rhodochrosite Rockhounding in Bonner County, Idaho

Updated June 2026

Conjecture Mine is a mapped rockhounding spot in Bonner County, Idaho. Reported finds include rhodochrosite. Below: coordinates, access notes, nearby spots, and trip-planning links.

Map showing Conjecture Mine in Bonner County, Idaho

Quick details

Access
Public area
State
Idaho
Postcode
83803

Geology at Conjecture Mine

This spot sits on Wallace Formation, middle and lower members, undivided, mapped as black argillite, siltite, dolomite, dolomitic limestone, and quartzite that formed roughly 1600 to 1000 million years ago. Carbonate rock like this dissolves and weathers readily, so fresh road cuts, quarries, and creek exposures are typically the most productive ground.

Mapped unit
Wallace Formation, middle and lower members, undivided
Age
1600–1000 Ma (Mesoproterozoic)
Rock types
black argillite, siltite, dolomite, dolomitic limestone, and quartzite
Elevation
3,190 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Best time to visit Conjecture Mine

Best months: April to October. Typical highs run 76°F in midsummer and 31°F in midwinter, with winter lows near 19°F.

Climate normals: NOAA 1991-2020 monthlies, BAYVIEW MODEL BASIN station (7 mi away), adjusted for elevation.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

State guidance last verified:

Found at Conjecture Mine

Each chip opens all spots that produce that material; the encyclopedia link opens the full ID and field guide.

Nearby rockhounding spots

Other rockhounding spots within driving distance of Conjecture Mine.

Across the state line from Conjecture Mine

Conjecture Mine is close enough to the Idaho border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Conjecture Mine FAQ

Where is Conjecture Mine?+
Conjecture Mine is in Bonner County, Idaho, at 47.91542, -116.43117.
What rocks and minerals can you find at Conjecture Mine?+
Conjecture Mine is reported to produce Rhodochrosite.
Is collecting allowed at Conjecture Mine?+
Generally open to casual rockhounding. Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig. Always confirm current rules with the managing agency before a trip.
What tools should I bring to Conjecture Mine?+
A rock hammer, sturdy gloves, safety glasses, and a collecting bag cover the basics here. Add a spray bottle: wet rock shows color and pattern that dry rock hides.
When is the best time to visit Conjecture Mine?+
The most comfortable months at Conjecture Mine are April to October.
How do I get to Conjecture Mine?+
Open the directions link to navigate to 47.91542, -116.43117 in Google Maps. Some spots are remote, so check road conditions before driving out.

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