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

Plan your visit

Generally open to casual rockhounding

County

Linn County

State

Iowa

Nearest road

29th Ave Dr SW

Postcode

52404

Coordinates

41.94186, -91.65122

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.

Access note: Collect loose coral and agate on public Cedar River gravel bars below the ordinary high-water mark. Do not collect in-place fossils at the Devonian Fossil Gorge near Coralville, a Corps of Engineers site where all collecting is prohibited; loose material in open river gravel at public accesses is the legal target.

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 Cedar Rapids

Comfortable months (45 to 90°F highs)

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).

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.

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.

• Iowa Geological Survey
• Iowa DNR state park rules
• Community submissions reviewed against published agency rules