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

Plan your visit

Generally open to casual rockhounding

County

Williams County

State

North Dakota

Nearest road

138th Avenue Northwest

Coordinates

48.11539, -103.70791

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

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.

Access note: Collect on public gravel bars away from Army Corps of Engineers project land; Lake Sakakawea and the managed Missouri shoreline are closed to collecting (36 CFR 327.14). Otherwise ask the landowner first. The Little Missouri National Grassland reaches into the county's south and allows USFS casual collecting.

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.

Best time to visit Williams County

Comfortable months (45 to 90°F highs)

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.

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.

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.

• North Dakota Geological Survey
• Dakota Prairie Grasslands
• North Dakota Parks and Recreation rules
• Community submissions reviewed against published agency rules