Mill Canyon: Tourmaline Rockhounding in Madison County, Montana

Updated June 2026

Mill Canyon is a mapped rockhounding spot in Madison County, Montana. Reported finds include tourmaline. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Madison County
State: Montana
Coordinates: 45.69677, -112.12467

Geology at Mill Canyon

This spot sits on Wyoming Province, meta-igneous rocks, quartzofeldspathic gneiss, southwestern Montana, mapped as granitic gneiss, tonalitic gneiss, quartz-feldspar-biotite gneiss, and hornblende-plagioclase gneiss that formed roughly 4030 to 2500 million years ago. Granitic rock like this is where pegmatite pockets tend to occur, the coarse-crystal settings that typically carry beryl, tourmaline, mica, and feldspar.

Mapped unit: Wyoming Province, meta-igneous rocks, quartzofeldspathic gneiss, southwestern Montana
Age: 4030–2500 Ma (Archean)
Rock types: granitic gneiss, tonalitic gneiss, quartz-feldspar-biotite gneiss, and hornblende-plagioclase gneiss
Elevation: 5,280 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 Mill Canyon

Best months: March to October. Typical highs run 82°F in midsummer and 33°F in midwinter, with winter lows near 11°F.

Climate normals: NOAA 1991-2020 monthlies, TWIN BRIDGES station (14 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 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 Mill Canyon

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

Tourmaline Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Mill Canyon.

Mill Canyon FAQ

Where is Mill Canyon?+

Mill Canyon is in Madison County, Montana, at 45.69677, -112.12467.

What rocks and minerals can you find at Mill Canyon?+

Mill Canyon is reported to produce Tourmaline.

Is collecting allowed at Mill Canyon?+

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 Mill Canyon?+

A rock hammer, a pry bar, gloves, and safety glasses suit pegmatite ground. Work weathered zones and check dump piles; coarse crystals often sit in decomposed rock.

When is the best time to visit Mill Canyon?+

The most comfortable months at Mill Canyon are March to October.

How do I get to Mill Canyon?+

Open the directions link to navigate to 45.69677, -112.12467 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in Montana

See all 87 Montana spots →

Open Mill Canyon on the map

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