Magpie Gulch: Green Sapphire Rockhounding in Lewis and Clark County, Montana

Quick details

Access

Public area

County

Lewis and Clark County

State

Montana

Nearest road

Magpie Gulch Road

Coordinates

46.66291, -111.66097

Geology at Magpie Gulch

This spot sits on Maywood Formation, Snowy Range Formation, Pilgrim Formation, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone, undivided, mapped as (limestone, dolomite)| (limestone, dolomite)| (clay shale)| (limestone, dolomite)| (micaceous shale, and siltstone)| (quartz sandstone) that formed roughly 510 to 495 million years ago. Loose deposits like these are float-collecting ground: erosion keeps moving durable rocks and minerals into gravel bars, cutbanks, and washes.

Mapped unit

Maywood Formation, Snowy Range Formation, Pilgrim Formation, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone, undivided

Age

510–495 Ma (Middle Cambrian)

Rock types

(limestone, dolomite)| (limestone, dolomite)| (clay shale)| (limestone, dolomite)| (micaceous shale, and siltstone)| (quartz sandstone)

Elevation

4,300 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 Magpie Gulch

Best months: March to October. Typical highs run 85°F in midsummer and 31°F in midwinter, with winter lows near 12°F.

Climate normals: NOAA 1991-2020 monthlies, HELENA AP ASOS station (16 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 Magpie Gulch

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

• Green SapphireEncyclopedia →