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Dry Cottonwood Creek: Sapphire Rockhounding in Deer Lodge County, Montana

Updated June 2026

Dry Cottonwood Creek is one of the historic Montana sapphire fields named by USGS and GIA, discovered after the Missouri River bars and before Rock Creek and Yogo Gulch. It is less accessible and less active than some better-known sapphire districts, but that documented place in the state's corundum history makes it too important to omit. Reported finds include sapphire. Below: coordinates, access notes, nearby spots, and trip-planning links.

Dry Cottonwood Creek photos

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

1 photo

Collectors screening fluvial gravel for sapphires at a Montana sapphire mine, representative of the sapphire digging at Dry Cottonwood Creek, Deer Lodge County, Montana

Quick details

Access: Public area
County: Deer Lodge County
State: Montana
Nearest road: cdt-alt Ley
Coordinates: 46.22060, -112.68514

Geology at Dry Cottonwood Creek

This spot sits on Biotite-hornblende granodioritic rocks along the Continental Divide, Anaconda Range, Sapphire Mountains, and Flint Creek Range, mapped as biotite-hornblende granodiorite, biotite-hornblende monzogranite, and tonalite that formed roughly 145 to 66 million years ago. Garnet and similar hard minerals typically weather out of rock like this and concentrate as resistant grains in nearby soils and creek gravels.

Mapped unit: Biotite-hornblende granodioritic rocks along the Continental Divide, Anaconda Range, Sapphire Mountains, and Flint Creek Range
Age: 145–66 Ma (Cretaceous)
Rock types: biotite-hornblende granodiorite, biotite-hornblende monzogranite, and tonalite
Elevation: 5,390 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 Dry Cottonwood Creek

Best months: April to October. Typical highs run 77°F in midsummer and 31°F in midwinter, with winter lows near 9°F.

Climate normals: NOAA 1991-2020 monthlies, DEER LODGE 3 W 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 Dry Cottonwood Creek

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

Sapphire Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Dry Cottonwood Creek.

Dry Cottonwood Creek FAQ

Where is Dry Cottonwood Creek?+

Dry Cottonwood Creek is in Deer Lodge County, Montana, at 46.22060, -112.68514. Nearest road: cdt-alt Ley.

What rocks and minerals can you find at Dry Cottonwood Creek?+

Dry Cottonwood Creek is reported to produce Sapphire.

Is collecting allowed at Dry Cottonwood 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 Dry Cottonwood Creek?+

A rock hammer, a sieve, and a small shovel work well for garnet-type minerals, which concentrate as resistant grains in soils and creek gravels.

When is the best time to visit Dry Cottonwood Creek?+

The most comfortable months at Dry Cottonwood Creek are April to October.

How do I get to Dry Cottonwood Creek?+

Open the directions link to navigate to 46.22060, -112.68514 in Google Maps. The nearest road is cdt-alt Ley.

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