Arnold: Geode Digging in Jefferson County, Missouri

Plan your visit

Generally open to casual rockhounding

County

Jefferson County

State

Missouri

Nearest road

Richardson Road

Postcode

63010

Coordinates

38.41917, -90.38958

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.

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 Arnold

Comfortable months (45 to 90°F highs)

Best months: February to December. Typical highs run 89°F in midsummer and 41°F in midwinter, with winter lows near 23°F.

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

Geology at Arnold

This spot sits on ground mapped as limestone that formed roughly 360 to 325 million years ago. Limestone country like this is classic geode ground: cavities in the carbonate rock can line themselves with quartz or calcite crystals.

Age

360–325 Ma (Mississippian)

Rock types

limestone

Elevation

540 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.

• Missouri Geological Survey
• Mark Twain National Forest
• Missouri State Parks rules
• Community submissions reviewed against published agency rules