Mammoth Creek: Onyx Rockhounding in Garfield County, Utah

Updated June 2026

Mammoth Creek is a mapped rockhounding spot in Garfield County, Utah. Reported finds include onyx. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Garfield County
State: Utah
Nearest road: US 89
Coordinates: 37.62800, -112.45823

Geology at Mammoth Creek

This spot sits on Stream alluvium, mapped as clay to boulder sized clasts that formed within roughly the last 12,000 years. Loose deposits like these are float-collecting ground: erosion keeps moving durable rocks and minerals into gravel bars, cutbanks, and washes.

Mapped unit: Stream alluvium
Age: < 1 Ma (Holocene)
Rock types: clay to boulder sized clasts
Elevation: 6,970 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 Mammoth Creek

Best months: March to November. Typical highs run 84°F in midsummer and 40°F in midwinter, with winter lows near 9°F.

Climate normals: NOAA 1991-2020 monthlies, HATCH station (2 mi away).

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 Utah, Rockhounding overview
Utah Geological Survey, collecting guidelines
SITLA, surface use rules
Community submissions reviewed against published agency rules

Found at Mammoth Creek

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

Onyx

Nearby rockhounding spots

Other rockhounding spots within driving distance of Mammoth Creek.

Across the state line from Mammoth Creek

Mammoth Creek is close enough to the Utah border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Glitter MountainMohave County, Arizona · 71 mi awaySelenite

Mammoth Creek FAQ

Where is Mammoth Creek?+

Mammoth Creek is in Garfield County, Utah, at 37.62800, -112.45823. Nearest road: US 89.

What rocks and minerals can you find at Mammoth Creek?+

Mammoth Creek is reported to produce Onyx.

Is collecting allowed at Mammoth Creek?+

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 Mammoth Creek?+

A rock hammer, sturdy gloves, safety glasses, and a collecting bag cover the basics here. Add a spray bottle: wet rock shows color and pattern that dry rock hides.

When is the best time to visit Mammoth Creek?+

The most comfortable months at Mammoth Creek are March to November.

How do I get to Mammoth Creek?+

Open the directions link to navigate to 37.62800, -112.45823 in Google Maps. The nearest road is US 89.

More rockhounding in Utah

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Open Mammoth Creek on the map

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