Jefferson River: Agate & Chalcedony Rockhounding in Madison County, Montana

Updated June 2026

Jefferson River is a mapped rockhounding spot in Madison County, Montana. Reported finds include agate, chalcedony, jasper, petrified wood. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Madison County
State: Montana
Nearest road: Primrose Lane
Postcode: 59751
Coordinates: 45.69019, -112.27452

Geology at Jefferson River

This spot sits on Alluvial deposits, mapped as sand and gravel that formed within roughly the last 3 million years. Petrified wood typically travels as tough float, and worked gravels like these are exactly where weathered pieces tend to collect.

Mapped unit: Alluvial deposits
Age: 3 Ma to present (Pleistocene to Holocene)
Rock types: sand and gravel
Elevation: 4,500 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 Jefferson River

Best months: March to November. Typical highs run 85°F in midsummer and 36°F in midwinter, with winter lows near 13°F.

Climate normals: NOAA 1991-2020 monthlies, TWIN BRIDGES station (10 mi away).

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 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 Jefferson River

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 Jefferson River.

Jefferson River FAQ

Where is Jefferson River?+

Jefferson River is in Madison County, Montana, at 45.69019, -112.27452. Nearest road: Primrose Lane.

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

Jefferson River is reported to produce Agate, Chalcedony, Jasper, Petrified Wood.

Is collecting allowed at Jefferson River?+

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 Jefferson River?+

A rock hammer, sturdy gloves, and a padded bag cover petrified wood hunting. Most pieces are surface float, so walking slopes and washes beats digging.

When is the best time to visit Jefferson River?+

The most comfortable months at Jefferson River are March to November.

How do I get to Jefferson River?+

Open the directions link to navigate to 45.69019, -112.27452 in Google Maps. The nearest road is Primrose Lane.

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