Challis: Red Agate & Banded Opal Rockhounding in Custer County, Idaho

Plan your visit

Generally open to casual rockhounding

County

Custer County

State

Idaho

Nearest road

Garden Creek Road

Coordinates

44.49401, -114.29990

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

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.

Access note: Use open public roads and land only. The broader Challis volcanic area includes private parcels, claims, and protected paleontological areas.

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.

Best time to visit Challis

Comfortable months (45 to 90°F highs)

Best months: March to October. Typical highs run 84°F in midsummer and 26°F in midwinter, with winter lows near 8°F.

Climate normals: NOAA 1991-2020 monthlies, CHALLIS AP station (5 mi away), adjusted for elevation.

Geology at Challis

This spot sits on Challis Volcanics, dacitic and rhyodacitic lava, mapped as dacite that formed roughly 56 to 34 million years ago. Volcanic ground like this is where agate, jasper, and other chalcedony typically form, filling old gas pockets and fracture seams in the flow rock.

Mapped unit

Challis Volcanics, dacitic and rhyodacitic lava

Age

56–34 Ma (Eocene)

Rock types

dacite

Elevation

5,910 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.

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

• Idaho Panhandle National Forests, Emerald Creek
• Idaho Geological Survey
• Spencer Opal Mines (fee-dig operator)
• Community submissions reviewed against published agency rules