Big Blue River: Agate & Chalcedony Rockhounding in Marshall County, Kansas

Quick details

Access

Permission required

County

Marshall County

State

Kansas

Nearest road

East Avenue

Postcode

66411

Coordinates

39.69102, -96.65462

Geology at Big Blue River

This spot sits on Alluvium, mapped as sand, silt, and clay that formed within roughly the last 3 million years. Gravels like these concentrate whatever survives the river: agate, jasper, and other tough silica typically show up as rounded, waxy stones.

Mapped unit

Alluvium

Age

3 Ma to present (Pleistocene to Holocene)

Rock types

sand, silt, and clay

Elevation

1,130 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 Big Blue River

Best months: March to November. Typical highs run 90°F in midsummer and 38°F in midwinter, with winter lows near 15°F.

Climate normals: NOAA 1991-2020 monthlies, MARYSVILLE station (10 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 Big Blue River

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

• AgateEncyclopedia →
• ChalcedonyEncyclopedia →
• ChertEncyclopedia →
• JasperEncyclopedia →