The geologic formations of Pictured Rocks National Lakeshore are most spectacularly represented by the 50-200 ft. sandstone cliffs that extend for more than 15 miles along the shoreline. Sea caves, arches, blowholes, turrets, stone spires, and other features like the famous Chapel Rock have been sculpted from these cliffs over the centuries by unceasing waves and weather.
The name "Pictured Rocks" comes from the streaks of mineral stain that decorate the cliffs. Stunning colors occur when groundwater oozes out of cracks and trickles down the rock face. Iron (red and orange), copper (blue and green), manganese (brown and black), and limonite (white) are among the most common color-producing minerals.
The best way to see the geologic layers and colors of the Pictured Rocks cliffs is from the water. Late afternoon or early evening sunlight brings out the richest colors.
What about Fossils?
Fossils are completely absent from the Jacobsville Formation and uncommon in the Munising Formation. Fragments of trilobites have been found in the Miners Castle member and 26 taxa of conodonts (ancient relatives of jawless fish) in the upper Munising Formation and the lower Au Train Formation. The Au Train also contains Middle Ordovician cephalopod and gastropod fossils.
Another major geologic feature of the lakeshore are the Grand Sable Dunes on the park's east end. Constantly moving and shifting, these dynamic dunes sit atop a high bluff of ancient glacial stone and rubble.
For more information ...
Lakeshore Geology site bulletin (pdf)
Grand Sable Dunes Research Natural Area site bulletin (pdf)
NPS Geology website
Last updated: May 26, 2019