Arnold: Geode Digging in Jefferson County, Missouri

Updated June 2026

Arnold is a mapped rockhounding spot in Jefferson County, Missouri. Reported finds include geode, dolomite, marcasite, pyrite, sphalerite, and more. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Jefferson County
State: Missouri
Nearest road: Richardson Road
Postcode: 63010
Coordinates: 38.41917, -90.38958

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.

Best time to visit Arnold

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).

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.

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 Arnold

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 Arnold.

Across the state line from Arnold

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

Arnold FAQ

Where is Arnold?+

Arnold is in Jefferson County, Missouri, at 38.41917, -90.38958. Nearest road: Richardson Road.

What rocks and minerals can you find at Arnold?+

Arnold is reported to produce Geode, Dolomite, Marcasite, Pyrite, Sphalerite, Calcite.

Is collecting allowed at Arnold?+

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. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Arnold?+

Bring a crack hammer, a chisel, safety glasses, and a bucket. Candidates are rounder and lighter than solid rock; a soil pipe cutter opens them cleaner than a flat smash.

When is the best time to visit Arnold?+

The most comfortable months at Arnold are February to December.

How do I get to Arnold?+

Open the directions link to navigate to 38.41917, -90.38958 in Google Maps. The nearest road is Richardson Road.

More rockhounding in Missouri

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Open Arnold on the map

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