Mound City: Petrified Wood & Opal Rockhounding in Campbell County, South Dakota

Plan your visit

Permission required before collecting

County

Campbell County

State

South Dakota

Coordinates

45.72064, -100.23723

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

Land & collecting status

Permission required before collecting

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

Access note: Collecting here centers on the gravels and bars of the Missouri River and its tributaries in Campbell County. On the bed of a navigable river, surface collecting of petrified wood and common rock is generally allowed, and any BLM tracts permit personal-use collecting without a permit. Much of the surrounding land is private ranch ground, so collectors should obtain landowner permission before searching off public river ground and avoid the federal reservoir lands managed by the Army Corps of Engineers without checking local rules.

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 Mound City

Comfortable months (45 to 90°F highs)

Best months: April to October. Typical highs run 85°F in midsummer and 24°F in midwinter, with winter lows near 3°F.

Climate normals: NOAA 1991-2020 monthlies, POLLOCK station (13 mi away).

Geology at Mound City

This spot sits on Pierre Shale, mapped as shale and bentonite 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

Pierre Shale

Age

100–66 Ma (Late Cretaceous)

Rock types

shale and bentonite

Elevation

1,760 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.

• BLM Montana-Dakotas rockhounding rules
• Buffalo Gap National Grassland
• South Dakota Geological Survey
• Community submissions reviewed against published agency rules