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Fossil Hunting in Minnesota

beginner friendly BrachiopodsBryozoansCrinoid stemsTrilobite fragmentsGastropods

Minnesota’s bluff country along the Mississippi River hides a rich record of Ordovician marine life. The state may be better known for lakes than fossils, but southeastern Minnesota’s limestone and shale exposures are a genuine paleontological resource.

Why Minnesota?

During the Ordovician period, roughly 450 million years ago, a shallow tropical sea covered what is now Minnesota. The Decorah Shale and Platteville Formation — deposited in this warm sea — are packed with marine invertebrate fossils. The Mississippi River and its tributaries have carved deep into these formations across southeastern Minnesota, creating the dramatic bluff country and exposing fossils in creek beds, road cuts, and river banks. The Twin Cities themselves sit atop Ordovician bedrock.

What You’ll Find

Ordovician marine fossils (~450 million years old):

  • Brachiopods — the most common find, many species with excellent shell preservation
  • Bryozoans — delicate colonial animals preserved as branching or encrusting forms
  • Crinoid stems — disc-shaped columnals from “sea lilies”
  • Trilobite fragments — Isotelus and Ceraurus fragments turn up in the Decorah Shale
  • Gastropods and cephalopods — snails and straight-shelled nautiloids
  • Receptaculites — the distinctive “sunflower coral” (actually a problematic fossil of uncertain affinity)

Best Time to Visit

  • Spring (April-June): Freeze-thaw weathering over winter breaks out fresh fossils
  • After heavy rain: Stream erosion in bluff country exposes new material
  • Fall: Pleasant temperatures and low water levels in creeks

Tips for Minnesota Collecting

  1. Start at Lilydale — it is the most accessible and well-known site in the state
  2. Check for closures — Lilydale sometimes closes due to bluff instability after heavy rain
  3. Explore creek beds in southeastern Minnesota’s bluff country for the best variety
  4. Split thin shale layers — the Decorah Shale parts easily along bedding planes to reveal fossils
  5. Visit the Science Museum of Minnesota in St. Paul for excellent paleontology exhibits and context

Collecting Sites

Lilydale Regional Park

Free Public Access

St. Paul, Ramsey County

A well-known urban fossil collecting site along the Mississippi River bluffs. Ordovician Platteville and Decorah formations are exposed in the park. Collecting from loose material is permitted. Check with the city for any seasonal access restrictions.

BrachiopodsTrilobite fragmentsGastropodsCephalopods

Decorah Shale Exposures (SE Minnesota)

Free Public Access

Fillmore and Houston Counties

Road cuts and stream exposures throughout the bluff country of southeastern Minnesota expose the fossil-rich Decorah Shale and Galena Group. Look for weathered-out fossils along creek beds.

BrachiopodsBryozoansCrinoid stemsTrilobite fragments

Forestville / Mystery Cave State Park

Public (Fee)

Fillmore County

Ordovician and Devonian fossils can be found in stream exposures and along trails. The cave itself is carved through Ordovician limestone. Surface collecting of loose material is permitted in the park.

BrachiopodsCrinoid stemsBryozoans

Minneapolis-St. Paul Road Cuts

Free Public Access

Hennepin and Ramsey Counties

Various road cuts and construction exposures in the Twin Cities metro area occasionally reveal Ordovician limestone and shale with marine fossils. Be alert during construction projects that excavate to bedrock.

BrachiopodsBryozoansGastropods

Legal Rules for Minnesota

Minnesota state parks generally allow surface collecting of loose fossils for personal use — do not excavate or use tools. Lilydale Regional Park in St. Paul allows fossil collecting but check for seasonal closures due to landslide risk. Road cut collecting is legal on public roads with appropriate safety precautions. Always get permission on private property. Vertebrate fossils on public land should be reported to the Science Museum of Minnesota.

Read our full legal guide for federal laws and more details.

Key Geological Formations

  • Decorah Shale (Ordovician)
  • Platteville Formation (Ordovician)
  • Galena Group (Ordovician)
  • St. Peter Sandstone (Ordovician)

Local Fossil Clubs & Museums