Big Horn Canyon: Agate & Chalcedony Rockhounding in Big Horn County, Montana
Updated July 2026
Big Horn Canyon is a mapped rockhounding spot in Big Horn County, Montana. Reported finds include agate, chalcedony, jasper, silicified coral, fossils. Below: coordinates, access notes, nearby spots, and trip-planning links.
Map showing Big Horn Canyon in Big Horn County, Montana
Quick details
- Access
- Permission required
- County
- Big Horn County
- State
- Montana
- Nearest road
- Route 211
- Postcode
- 59035
- Coordinates
- 45.31296, -107.96042
Geology at Big Horn Canyon
This spot sits on Amsden Formation, mapped as shale and limestone that formed roughly 330 to 315 million years ago. Limestone like this typically forms in ancient seas, so marine fossils such as brachiopods, corals, and crinoids tend to weather out of fresh exposures.
- Mapped unit
- Amsden Formation
- Age
- 330–315 Ma (Mississippian to Pennsylvanian)
- Rock types
- shale and limestone
- Elevation
- 3,750 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 Big Horn Canyon
Best months: March to November. Typical highs run 87°F in midsummer and 37°F in midwinter, with winter lows near 18°F.
Climate normals: NOAA 1991-2020 monthlies, YELLOWTAIL DAM station (1 mi away), adjusted for elevation.
Land & collecting status
Permission required before collecting
Requires landowner or agency permission before any collecting. Do not enter without explicit authorization.
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:
- BLM Montana — Recreational mineral collecting
- Montana Bureau of Mines and Geology
- Gem Mountain Sapphire Mine (fee-dig operator)
- Community submissions reviewed against published agency rules
Found at Big Horn Canyon
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 Big Horn Canyon.
- Pryor MountainsTop pick in MontanaBig Horn County, Montana · 16 mi awayFossils, Agate, Chalcedony
- Bear CanyonCarbon County, Montana · 32 mi awayGeode, Agate
- Yellowstone River (Billings area)Top pick in MontanaYellowstone County, Montana · 44 mi awayMontana Agate, Chalcedony, Chert
- FrombergCarbon County, Montana · 47 mi awayCoal, Pyrite
- HyshamTreasure County, Montana · 71 mi awayMoss Agate
- Old Nye Picnic AreaStillwater County, Montana · 94 mi awaySilver
Across the state line from Big Horn Canyon
Big Horn Canyon is close enough to the Montana border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.
- Big Horn RiverBig Horn County, Wyoming · 28 mi awayDry Head Agate
- LovellBig Horn County, Wyoming · 36 mi awayFossils, Ammonites, Dinosaur Bones
- LovellBig Horn County, Wyoming · 40 mi awayGypsum, Fossils
- GreybullBig Horn County, Wyoming · 47 mi awayGastroliths, Petrified Dinosaur Bone, Fossils
- Red GulchBig Horn County, Wyoming · 55 mi awayGypsum
- HyattvilleBig Horn County, Wyoming · 77 mi awayGypsum, Dinosaur Bones, Gastroliths
Big Horn Canyon FAQ
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More rockhounding in Montana
See all 87 Montana spots →Open Big Horn Canyon on the map
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