Cannonball River: Agate & Chalcedony Rockhounding in Sioux County, North Dakota

Updated July 2026

Cannonball River is a mapped rockhounding spot in Sioux County, North Dakota. Reported finds include agate, chalcedony, silicified wood, jasper. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Permission required
County: Sioux County
State: North Dakota
Coordinates: 46.35956, -100.94306

Geology at Cannonball River

This spot sits on Hell Creek Formation, mapped as sandstone, siltstone, and claystone that formed roughly 100 to 66 million years ago. Sedimentary beds like these are the typical host for petrified and silicified wood, which weathers out as durable float on slopes and in washes.

Mapped unit: Hell Creek Formation
Age: 100–66 Ma (Late Cretaceous)
Rock types: sandstone, siltstone, and claystone
Elevation: 1,690 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 Cannonball River

Best months: April to October. Typical highs run 86°F in midsummer and 25°F in midwinter, with winter lows near 1°F.

Climate normals: NOAA 1991-2020 monthlies, BREIEN station (1 mi away).

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.

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

Found at Cannonball River

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 Cannonball River.

Across the state line from Cannonball River

Cannonball River is close enough to the North Dakota border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Cannonball River FAQ

Where is Cannonball River?+

Cannonball River is in Sioux County, North Dakota, at 46.35956, -100.94306.

What rocks and minerals can you find at Cannonball River?+

Cannonball River is reported to produce Agate, Chalcedony, Silicified Wood, Jasper.

Is collecting allowed at Cannonball River?+

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 Cannonball River?+

A rock hammer, sturdy gloves, and a padded bag cover petrified wood hunting. Most pieces are surface float, so walking slopes and washes beats digging.

When is the best time to visit Cannonball River?+

The most comfortable months at Cannonball River are April to October.

How do I get to Cannonball River?+

Open the directions link to navigate to 46.35956, -100.94306 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in North Dakota

See all 25 North Dakota spots →

Open Cannonball River on the map

Use the RockHoundR app for live land overlays, weather, geology, directions, and saved finds.