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Cedar Rapids: Silicified Coral & Calcified Coral Rockhounding in Linn County, Iowa

Updated July 2026

The Cedar River gravels around Cedar Rapids carry silicified Devonian coral weathered out of the Cedar Valley Group limestones that underlie eastern Iowa. Colonial corals such as Hexagonaria and Favosites survive as hard, silica-replaced heads that take a good polish. The same gravels yield glacial agates and jaspers, making this a productive mixed-bag stretch. Reported finds include silicified coral, calcified coral. Below: coordinates, access notes, nearby spots, and trip-planning links.

Cedar Rapids photos

Public image records connected to this spot or its reported material.

1 photo

The Cedar River and a railroad bridge at Cedar Rapids, Linn County, Iowa

Quick details

Access: Public area
County: Linn County
State: Iowa
Nearest road: 29th Ave Dr SW
Postcode: 52404
Coordinates: 41.94186, -91.65122

Geology at Cedar Rapids

This spot sits on ground mapped as Scotch Grove Formation that formed roughly 440 to 425 million years ago. Fossils here are typically found in fresh exposures, where erosion keeps bringing new material to the surface.

Mapped unit: Scotch Grove Formation
Age: 440–425 Ma (Llandovery to Wenlock)
Elevation: 720 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 Cedar Rapids

Best months: March to November. Typical highs run 83°F in midsummer and 28°F in midwinter, with winter lows near 12°F.

Climate normals: NOAA 1991-2020 monthlies, CEDAR RAPIDS MUNI AP station (6 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 Cedar Rapids

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 Cedar Rapids.

Across the state line from Cedar Rapids

Cedar Rapids 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.

Cedar Rapids FAQ

Where is Cedar Rapids?+

Cedar Rapids is in Linn County, Iowa, at 41.94186, -91.65122. Nearest road: 29th Ave Dr SW.

What rocks and minerals can you find at Cedar Rapids?+

Cedar Rapids is reported to produce Silicified Coral, Calcified Coral.

Is collecting allowed at Cedar Rapids?+

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 Cedar Rapids?+

A rock hammer, a cold chisel, safety glasses, and newspaper or foam for wrapping finds cover most fossil ground. A trowel and a sieve help in soft exposures.

When is the best time to visit Cedar Rapids?+

The most comfortable months at Cedar Rapids are March to November.

How do I get to Cedar Rapids?+

Open the directions link to navigate to 41.94186, -91.65122 in Google Maps. The nearest road is 29th Ave Dr SW.

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