Best spot

Williams County: Montana Moss Agate & Red Jasper Rockhounding in Williams County, North Dakota

Updated July 2026

Williams County ranks among North Dakota's better counties for Montana moss agate and jasper, which wash into the Missouri and Yellowstone river gravels and glacial drift of the state's northwest corner. Red and yellow jasper accompany the agate along gravel bars and cutbanks. Much of the Missouri River and Lake Sakakawea shoreline here is Army Corps of Engineers land where collecting is prohibited, so legal hunting is on non-Corps gravel bars and on private land with permission. Reported finds include montana moss agate, red jasper, yellow jasper. Below: coordinates, access notes, nearby spots, and trip-planning links.

Williams County photos

Public image records connected to this spot or its reported material.

1 photo

The Missouri and Yellowstone rivers meeting near Williston, Williams County, North Dakota

Quick details

Access: Public area
County: Williams County
State: North Dakota
Nearest road: 138th Avenue Northwest
Coordinates: 48.11539, -103.70791

Geology at Williams County

This spot sits on Bullion Creek Formation, mapped as claystone and siltstone that formed roughly 66 to 56 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: Bullion Creek Formation
Age: 66–56 Ma (Paleocene)
Rock types: claystone and siltstone
Elevation: 1,840 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 Williams County

Best months: April to October. Typical highs run 86°F in midsummer and 25°F in midwinter, with winter lows near 5°F.

Climate normals: NOAA 1991-2020 monthlies, WILLISTON EXP FARM station (2 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.

Sources: RockHoundR public spot dataset, app land overlays, and local agency review before each trip.

Found at Williams County

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 Williams County.

Williams County FAQ

Where is Williams County?+

Williams County is in Williams County, North Dakota, at 48.11539, -103.70791. Nearest road: 138th Avenue Northwest.

What rocks and minerals can you find at Williams County?+

Williams County is reported to produce Montana Moss Agate, Red Jasper, Yellow Jasper.

Is collecting allowed at Williams County?+

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 Williams County?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Williams County?+

The most comfortable months at Williams County are April to October.

How do I get to Williams County?+

Open the directions link to navigate to 48.11539, -103.70791 in Google Maps. The nearest road is 138th Avenue Northwest.

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