KELLEYS ISLAND, Ohio — The Glacial Grooves on Kelleys Island are the largest and most accessible example of this geological phenomenon anywhere in the world. The location is designated as a National Natural Landmark.

According to the Ohio History Connection, the grooves are accessible daily in season, weather permitting, via the Kelleys Island Ferry departing from Marblehead. From a walkway, footbridge and stairs, you can look down on the immense grooves.

The grooves are 400 feet long, 35 feet wide, and up to 10 feet deep. Archaeologist and Site Manager Bill Kennedy said the grooves are composed of Devonian limestone and contain marine fossils that are 350 to 400 million years old. 

Glacial Grooves Geological Preserve is managed by the Ohio Department of Natural Resources Kelley Island State Parks.