Best spot

Sweetwater River: Agate Rockhounding in Fremont County, Wyoming

Updated July 2026

Sweetwater agate is Wyoming's signature agate, and the Sweetwater River drainage is the classic field area tied to the Granite Mountains source terrain. WSGS publications describe Sweetwater material among the state's better-known agates, while BLM rules make casual surface collecting possible on open public parcels when claims and ownership are checked first. Reported finds include agate. Below: coordinates, access notes, nearby spots, and trip-planning links.

Sweetwater River photos

Public image records connected to this spot or its reported material.

4 photos

Quick details

Access: Permission required
County: Fremont County
State: Wyoming
Coordinates: 42.44731, -108.99584

Geology at Sweetwater River

This spot sits on ground mapped as volcanic, sandstone, and conglomerate that formed roughly 56 to 23 million years ago. Volcanic ground like this is where agate, jasper, and other chalcedony typically form, filling old gas pockets and fracture seams in the flow rock.

Age: 56–23 Ma (Eocene to Oligocene)
Rock types: volcanic, sandstone, and conglomerate
Elevation: 7,680 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 Sweetwater River

Best months: April to October. Typical highs run 78°F in midsummer and 29°F in midwinter, with winter lows near 3°F. At about 7,680 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

Climate normals: NOAA 1991-2020 monthlies, SOUTH PASS CITY station (10 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 Sweetwater River

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

Agate Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Sweetwater River.

Sweetwater River FAQ

Where is Sweetwater River?+

Sweetwater River is in Fremont County, Wyoming, at 42.44731, -108.99584.

What rocks and minerals can you find at Sweetwater River?+

Sweetwater River is reported to produce Agate.

Is collecting allowed at Sweetwater River?+

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 Sweetwater River?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Sweetwater River?+

The most comfortable months at Sweetwater River are April to October. At about 7,680 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

How do I get to Sweetwater River?+

Open the directions link to navigate to 42.44731, -108.99584 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in Wyoming

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