Jack Creek: Dumortierite Rockhounding in Jefferson County, Montana

Updated June 2026

Jack Creek is a mapped rockhounding spot in Jefferson County, Montana. Reported finds include dumortierite. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Jefferson County
State: Montana
Nearest road: Jack Creek Road
Coordinates: 46.37254, -112.28725

Geology at Jack Creek

This spot sits on Boulder batholith, Butte Quartz Monzonite, mapped as quartz monzonite and monzogranite-to-granodiorite that formed roughly 100 to 66 million years ago. Plutonic rock like this weathers slowly into grus and boulders, and the most productive collecting is typically in weathered zones and drainages.

Mapped unit: Boulder batholith, Butte Quartz Monzonite
Age: 100–66 Ma (Late Cretaceous)
Rock types: quartz monzonite and monzogranite-to-granodiorite
Elevation: 7,120 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 Jack Creek

Best months: April to October. Typical highs run 73°F in midsummer and 27°F in midwinter, with winter lows near 2°F. At about 7,120 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

Climate normals: NOAA 1991-2020 monthlies, TIZER GARDENS station (13 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 Jack Creek

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

Dumortierite

Nearby rockhounding spots

Other rockhounding spots within driving distance of Jack Creek.

Jack Creek FAQ

Where is Jack Creek?+

Jack Creek is in Jefferson County, Montana, at 46.37254, -112.28725. Nearest road: Jack Creek Road.

What rocks and minerals can you find at Jack Creek?+

Jack Creek is reported to produce Dumortierite.

Is collecting allowed at Jack Creek?+

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 Jack Creek?+

A rock hammer, sturdy gloves, safety glasses, and a collecting bag cover the basics here. Add a spray bottle: wet rock shows color and pattern that dry rock hides.

When is the best time to visit Jack Creek?+

The most comfortable months at Jack Creek are April to October. At about 7,120 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

How do I get to Jack Creek?+

Open the directions link to navigate to 46.37254, -112.28725 in Google Maps. The nearest road is Jack Creek Road.

More rockhounding in Montana

See all 87 Montana spots →

Open Jack Creek on the map

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