Alum Mountain: Geode Digging in Grant County, New Mexico

Updated June 2026

Alum Mountain is a mapped rockhounding spot in Grant County, New Mexico. Reported finds include geode, carnelian. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Permission required
County: Grant County
State: New Mexico
Coordinates: 33.13255, -108.21916

Geology at Alum Mountain

This spot sits on Lower-upper middle Tertiary basaltic andesites and andesites of the Mogollon Group, mapped as andesite, basaltic andesite, and basalt that formed roughly 34 to 23 million years ago. Volcanic rock like this is classic geode and thunderegg country: gas cavities in the old flows can line themselves with quartz or agate over time.

Mapped unit: Lower-upper middle Tertiary basaltic andesites and andesites of the Mogollon Group
Age: 34–23 Ma (Early Oligocene to Late Oligocene)
Rock types: andesite, basaltic andesite, and basalt
Elevation: 6,330 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 Alum Mountain

Conditions here are workable year-round, with typical highs from 54°F in winter to 87°F in summer.

Climate normals: NOAA 1991-2020 monthlies, GILA HOT SPRINGS station (5 mi away), adjusted for elevation.

Land & collecting status

Permission required before collecting

Requires landowner or agency permission before any collecting. Do not enter without explicit authorization.

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

Rockhound State Park — Collection rules
BLM New Mexico
New Mexico Bureau of Geology and Mineral Resources
Community submissions reviewed against published agency rules

Found at Alum Mountain

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 Alum Mountain.

Across the state line from Alum Mountain

Alum Mountain is close enough to the New Mexico border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Alum Mountain FAQ

Where is Alum Mountain?+

Alum Mountain is in Grant County, New Mexico, at 33.13255, -108.21916.

What rocks and minerals can you find at Alum Mountain?+

Alum Mountain is reported to produce Geode, Carnelian.

Is collecting allowed at Alum Mountain?+

Permission required before collecting. Requires landowner or agency permission before any collecting. Do not enter without explicit authorization. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Alum Mountain?+

Bring a crack hammer, a chisel, safety glasses, and a bucket. Candidates are rounder and lighter than solid rock; a soil pipe cutter opens them cleaner than a flat smash.

When is the best time to visit Alum Mountain?+

Alum Mountain is workable year-round.

How do I get to Alum Mountain?+

Open the directions link to navigate to 33.13255, -108.21916 in Google Maps. Some spots are remote, so check road conditions before driving out.

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Open Alum Mountain on the map

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