Greybull: Fossil Hunting in Big Horn County, Wyoming

Updated June 2026

Greybull is a mapped rockhounding spot in Big Horn County, Wyoming. Reported finds include gastroliths, petrified dinosaur bone, fossils. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Big Horn County
State: Wyoming
Coordinates: 44.64648, -107.80699

Geology at Greybull

This spot sits on Chugwater and Goose Egg Formations, mapped as siltstone and sandstone that formed roughly 300 to 200 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: Chugwater and Goose Egg Formations
Age: 300–200 Ma (Permian to Late Triassic)
Rock types: siltstone and sandstone
Elevation: 5,030 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 Greybull

Best months: March to October. Typical highs run 86°F in midsummer and 30°F in midwinter, with winter lows near 4°F.

Climate normals: NOAA 1991-2020 monthlies, SHELL station (8 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: April 1, 2026

BLM Wyoming
Wyoming State Geological Survey
Fossil Butte National Monument
Community submissions reviewed against published agency rules

Found at Greybull

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 Greybull.

Across the state line from Greybull

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

Greybull FAQ

Where is Greybull?+

Greybull is in Big Horn County, Wyoming, at 44.64648, -107.80699.

What rocks and minerals can you find at Greybull?+

Greybull is reported to produce Gastroliths, Petrified Dinosaur Bone, Fossils.

Is collecting allowed at Greybull?+

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 Greybull?+

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 Greybull?+

The most comfortable months at Greybull are March to October.

How do I get to Greybull?+

Open the directions link to navigate to 44.64648, -107.80699 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in Wyoming

See all 82 Wyoming spots →

Open Greybull on the map

Use the RockHoundR app for live land overlays, weather, geology, directions, and saved finds.