Finnegan Ridge: Chert & Jasper Rockhounding in Madison County, Montana

Updated July 2026

Finnegan Ridge is a mapped rockhounding spot in Madison County, Montana. Reported finds include chert, jasper. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Permission required
County: Madison County
State: Montana
Coordinates: 45.50377, -111.38319

Geology at Finnegan Ridge

This spot sits on Madison Group: Mission Canyon and Lodgepole Formations; or Castle Reef and Allan Mountain Formations, mapped as limestone, dolostone, and black shale that formed roughly 360 to 330 million years ago. Chert and agate nodules typically form inside carbonate rock like this and weather out as tough, waxy lumps in soils and creek beds.

Mapped unit: Madison Group: Mission Canyon and Lodgepole Formations; or Castle Reef and Allan Mountain Formations
Age: 360–330 Ma (Mississippian)
Rock types: limestone, dolostone, and black shale
Elevation: 6,380 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 Finnegan Ridge

Best months: April to October. Typical highs run 80°F in midsummer and 33°F in midwinter, with winter lows near 18°F.

Climate normals: NOAA 1991-2020 monthlies, NORRIS MADISON PWR HOUSE station (12 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 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 Finnegan Ridge

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 Finnegan Ridge.

Finnegan Ridge FAQ

Where is Finnegan Ridge?+

Finnegan Ridge is in Madison County, Montana, at 45.50377, -111.38319.

What rocks and minerals can you find at Finnegan Ridge?+

Finnegan Ridge is reported to produce Chert, Jasper.

Is collecting allowed at Finnegan Ridge?+

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 Finnegan Ridge?+

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 Finnegan Ridge?+

The most comfortable months at Finnegan Ridge are April to October.

How do I get to Finnegan Ridge?+

Open the directions link to navigate to 45.50377, -111.38319 in Google Maps. Some spots are remote, so check road conditions before driving out.

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