Parker Mountain: Agate & Chalcedony Rockhounding in Lemhi County, Idaho

Quick details

Access

Public area

County

Lemhi County

State

Idaho

Nearest road

National Forest Development Road 68

Coordinates

44.60682, -114.54581

Geology at Parker Mountain

This spot sits on Challis Volcanics, Twin Peaks caldera, tuff of Challis Creek, caldera-wall slump debris, megabreccia, mapped as megabreccia that formed roughly 56 to 34 million years ago. Tough silica like agate, jasper, and chert typically weathers out of beds like these and collects as float in drainages and on deflation surfaces.

Mapped unit

Challis Volcanics, Twin Peaks caldera, tuff of Challis Creek, caldera-wall slump debris, megabreccia

Age

56–34 Ma (Eocene)

Rock types

megabreccia

Elevation

8,580 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 Parker Mountain

Best months: May to October. Typical highs run 74°F in midsummer and 17°F in midwinter, with winter lows near -2°F. At about 8,580 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

Climate normals: NOAA 1991-2020 monthlies, CHALLIS AP station (17 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

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

Found at Parker Mountain

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

• AgateEncyclopedia →
• ChalcedonyEncyclopedia →