Shell Rock: Lake Superior Agate Rockhounding in Butler County, Iowa

Updated June 2026

Shell Rock is a mapped rockhounding spot in Butler County, Iowa. Reported finds include lake superior agate. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Butler County
State: Iowa
Nearest road: State Highway 3
Postcode: 50670
Coordinates: 42.72656, -92.58632

Geology at Shell Rock

This spot sits on ground mapped as Cedar Valley Group that formed roughly 390 to 370 million years ago. Tough silica like agate and jasper typically survives weathering and collects as float in drainages and gravel.

Mapped unit: Cedar Valley Group
Age: 390–370 Ma (Middle Devonian to Late Devonian)
Elevation: 910 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 Shell Rock

Best months: April to November. Typical highs run 83°F in midsummer and 25°F in midwinter, with winter lows near 8°F.

Climate normals: NOAA 1991-2020 monthlies, ALLISON station (11 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 Shell Rock

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

Lake Superior Agate Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Shell Rock.

Across the state line from Shell Rock

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

Shell Rock FAQ

Where is Shell Rock?+

Shell Rock is in Butler County, Iowa, at 42.72656, -92.58632. Nearest road: State Highway 3.

What rocks and minerals can you find at Shell Rock?+

Shell Rock is reported to produce Lake Superior Agate.

Is collecting allowed at Shell Rock?+

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 Shell Rock?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Shell Rock?+

The most comfortable months at Shell Rock are April to November.

How do I get to Shell Rock?+

Open the directions link to navigate to 42.72656, -92.58632 in Google Maps. The nearest road is State Highway 3.

More rockhounding in Iowa

See all 49 Iowa spots →

Open Shell Rock on the map

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