Thermopolis: Copper & Limonite Rockhounding in Fremont County, Wyoming

Updated July 2026

Thermopolis is a mapped rockhounding spot in Fremont County, Wyoming. Reported finds include copper, limonite. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Permission required
County: Fremont County
State: Wyoming
Nearest road: Arapahoe Ranch Road
Coordinates: 43.51100, -108.62583

Geology at Thermopolis

This spot sits on Cloverly, Morrison, Sundance, and Gypsum Spring Formations and Nugget Sandstone, mapped as sandstone, claystone, and shale that formed roughly 250 to 100 million years ago. Sedimentary rock like this erodes unevenly, so the most productive collecting is typically along fresh cuts, badland slopes, and active drainages.

Mapped unit: Cloverly, Morrison, Sundance, and Gypsum Spring Formations and Nugget Sandstone
Age: 250–100 Ma (Triassic to Early Cretaceous)
Rock types: sandstone, claystone, and shale
Elevation: 6,370 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.

Best time to visit Thermopolis

Best months: March to October. Typical highs run 83°F in midsummer and 36°F in midwinter, with winter lows near 7°F.

Climate normals: NOAA 1991-2020 monthlies, THERMOPOLIS 21WNW station (15 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: April 1, 2026

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

Found at Thermopolis

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 Thermopolis.

Thermopolis FAQ

Where is Thermopolis?+

Thermopolis is in Fremont County, Wyoming, at 43.51100, -108.62583. Nearest road: Arapahoe Ranch Road.

What rocks and minerals can you find at Thermopolis?+

Thermopolis is reported to produce Copper, Limonite.

Is collecting allowed at Thermopolis?+

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 Thermopolis?+

A rock hammer, gloves, and safety glasses are enough for oxidized copper ground. Look for green and blue staining on weathered rock and in old dump piles.

When is the best time to visit Thermopolis?+

The most comfortable months at Thermopolis are March to October.

How do I get to Thermopolis?+

Open the directions link to navigate to 43.51100, -108.62583 in Google Maps. The nearest road is Arapahoe Ranch Road.

More rockhounding in Wyoming

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Open Thermopolis on the map

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