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Pryor Mountains: Fossil Hunting in Big Horn County, Montana

Permission requiredBest spot5 mineralsBig Horn County, MontanaUpdated July 2026
Minerals reported
5
Elevation
4,370 ft
Best months
March to October

The Pryor Mountains stand out for Dryhead-style agate, with Mindat listing agate and chalcedony from the range and a named Dryhead Agate Mine in the Bighorn River area. The same Big Horn County country also carries fossil-bearing sedimentary units, so the locality needs careful land-status and fossil-rule checks rather than casual blanket collecting. Reported finds include fossil, agate, chalcedony, jasper, petrified wood. Below: coordinates, access notes, nearby spots, and trip-planning links.

Plan your visit

Permission required before collecting

State
Montana
Nearest road
Bad Pass Road
Get directionsView on Google Maps

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Permission required before collecting

Requires landowner or agency permission before any collecting. Do not enter without explicit authorization.

Access note: Check BLM, Forest Service, tribal, private, and claim boundaries carefully; collect only common rocks and invertebrate or plant fossils where rules allow.

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.

Best time to visit Pryor Mountains

Comfortable months (45 to 90°F highs)

Best months: March to October. Typical highs run 85°F in midsummer and 35°F in midwinter, with winter lows near 16°F.

Climate normals: NOAA 1991-2020 monthlies, YELLOWTAIL DAM station (17 mi away), adjusted for elevation.

Geology at Pryor Mountains

This spot sits on Tensleep Formation, mapped as sandstone that formed roughly 315 to 305 million years ago. Sedimentary layers like these are where fossils are typically preserved, and fresh exposures after rain or in active cuts tend to produce best.

Mapped unit
Tensleep Formation
Age
315–305 Ma (Pennsylvanian)
Rock types
sandstone
Elevation
4,370 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.

Today's weather

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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 Pryor Mountains

Each name 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 Pryor Mountains.

Across the state line from Pryor Mountains

Pryor Mountains 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 · 19 mi awayDry Head Agate
  • LovellBig Horn County, Wyoming · 32 mi awayFossil, Ammonite, Dinosaur Bone
  • LovellBig Horn County, Wyoming · 33 mi awayGypsum, Fossil
  • GreybullBig Horn County, Wyoming · 47 mi awayGastrolith, Petrified Dinosaur Bone, Fossil
  • Red GulchBig Horn County, Wyoming · 54 mi awayGypsum
  • Cedar MountainPark County, Wyoming · 67 mi awayTravertine

Pryor Mountains FAQ

Where is Pryor Mountains?+
Pryor Mountains is in Big Horn County, Montana, at 45.23857, -108.26747. Nearest road: Bad Pass Road.
What rocks and minerals can you find at Pryor Mountains?+
Pryor Mountains is reported to produce Fossil, Agate, Chalcedony, Jasper, Petrified Wood.
Is collecting allowed at Pryor Mountains?+
Permission required before collecting. Requires landowner or agency permission before any collecting. Do not enter without explicit authorization. Always confirm current rules with the managing agency before a trip.
What tools should I bring to Pryor Mountains?+
A rock hammer, a cold chisel, safety glasses, and newspaper or foam for wrapping finds cover most fossil ground. A trowel and a sieve help in soft exposures.
When is the best time to visit Pryor Mountains?+
The most comfortable months at Pryor Mountains are March to October.
How do I get to Pryor Mountains?+
Open the directions link to navigate to 45.23857, -108.26747 in Google Maps. The nearest road is Bad Pass Road.

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