Malm Gulch: Agate & Petrified Wood Rockhounding in Custer County, Idaho

Updated June 2026

Malm Gulch is a mapped rockhounding spot in Custer County, Idaho. Reported finds include agate, petrified wood. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Custer County
State: Idaho
Nearest road: Malm Gulch Trail
Coordinates: 44.33834, -114.22255

Geology at Malm Gulch

This spot sits on Challis Volcanics, sedimentary and volcanic rocks, mapped as volcanic sandstone, conglomerate, siltstone, and mudstone that formed roughly 56 to 34 million years ago. Petrified wood typically comes from volcanic ash beds like the ones associated with this ground, where buried forests were slowly replaced by silica.

Mapped unit: Challis Volcanics, sedimentary and volcanic rocks
Age: 56–34 Ma (Eocene)
Rock types: volcanic sandstone, conglomerate, siltstone, and mudstone
Elevation: 5,990 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 Malm Gulch

Best months: March to October. Typical highs run 83°F in midsummer and 26°F in midwinter, with winter lows near 7°F.

Climate normals: NOAA 1991-2020 monthlies, CHALLIS AP 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

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

Found at Malm Gulch

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

Nearby rockhounding spots

Other rockhounding spots within driving distance of Malm Gulch.

Malm Gulch FAQ

Where is Malm Gulch?+

Malm Gulch is in Custer County, Idaho, at 44.33834, -114.22255. Nearest road: Malm Gulch Trail.

What rocks and minerals can you find at Malm Gulch?+

Malm Gulch is reported to produce Agate, Petrified Wood.

Is collecting allowed at Malm Gulch?+

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 Malm Gulch?+

A rock hammer, sturdy gloves, and a padded bag cover petrified wood hunting. Most pieces are surface float, so walking slopes and washes beats digging.

When is the best time to visit Malm Gulch?+

The most comfortable months at Malm Gulch are March to October.

How do I get to Malm Gulch?+

Open the directions link to navigate to 44.33834, -114.22255 in Google Maps. The nearest road is Malm Gulch Trail.

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Open Malm Gulch on the map

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