Custer County: Montana Agate Rockhounding in Custer County, Montana

Updated June 2026

Custer County is a mapped rockhounding spot in Custer County, Montana. Reported finds include montana agate. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Custer County
State: Montana
Postcode: 59301
Coordinates: 46.39627, -105.89810

Geology at Custer County

This spot sits on Alluvium, mapped as gravel, sand, and silt that formed within roughly the last 2 million years. Gravels like these concentrate whatever survives the river: agate, jasper, and other tough silica typically show up as rounded, waxy stones.

Mapped unit: Alluvium
Age: 2 Ma to present (Pleistocene to Holocene)
Rock types: gravel, sand, and silt
Elevation: 2,340 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 Custer County

Best months: March to November. Typical highs run 90°F in midsummer and 31°F in midwinter, with winter lows near 10°F.

Climate normals: NOAA 1991-2020 monthlies, MILES CITY AP station (2 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 Custer County

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

Montana Agate Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Custer County.

Custer County FAQ

Where is Custer County?+

Custer County is in Custer County, Montana, at 46.39627, -105.89810.

What rocks and minerals can you find at Custer County?+

Custer County is reported to produce Montana Agate.

Is collecting allowed at Custer County?+

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 Custer County?+

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 Custer County?+

The most comfortable months at Custer County are March to November.

How do I get to Custer County?+

Open the directions link to navigate to 46.39627, -105.89810 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in Montana

See all 87 Montana spots →

Open Custer County on the map

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