Bremer County: Coldwater Agate Rockhounding in Bremer County, Iowa

Quick details

Access

Public area

County

Bremer County

State

Iowa

Nearest road

160th Street

Postcode

50676

Coordinates

42.82249, -92.32725

Geology at Bremer County

This spot sits on ground mapped as Hopkinton Fm, Blanding Fm, Tete des Morts Fm, Mosalem Fm that formed roughly 445 to 440 million years ago. Tough silica like agate and jasper typically survives weathering and collects as float in drainages and gravel.

Mapped unit

Hopkinton Fm, Blanding Fm, Tete des Morts Fm, Mosalem Fm

Age

445–440 Ma (Llandovery)

Elevation

1,050 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 Bremer County

Best months: April to October. Typical highs run 83°F in midsummer and 25°F in midwinter, with winter lows near 7°F.

Climate normals: NOAA 1991-2020 monthlies, TRIPOLI station (4 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 Bremer County

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

• Coldwater AgateEncyclopedia →