Kelleys Island Glacial Grooves

About 18,000 years ago the Wisconsinan ice sheet was moving south across what is now Lake Erie, and it had rock frozen into its underside. That rock got dragged across the limestone bedrock of Kelleys Island under the weight of a mile of ice. What it left is a set of parallel grooves — the largest exposed glacial grooves accessible anywhere in the world.

The main slab runs roughly 400 feet long, 35 feet wide, and up to 15 feet deep. Standing at the rail looking down into it, the scale is hard to argue with. This is the ice sheet’s tool marks, at full size.

What you are looking at

Two things are going on in the same rock.

The grooves are glacial: smooth, parallel, oriented northwest to southeast, with polish and fine striations on the surfaces where finer material acted as sandpaper.

The fossils are much older. The bedrock is Devonian limestone, laid down as sea floor roughly 350 to 400 million years ago, and the groove walls cut through it in section. Corals, brachiopods, crinoid stems and gastropods are visible in the exposed faces. You are looking at a tropical reef bed carved by an ice age.

Quarrying on Kelleys Island in the nineteenth century destroyed a much larger grooved area than what survives. What is protected today is a fraction of what was here. The state acquired and preserved the remaining slab in the 1930s.

Visiting

The preserve is small and free. A walkway with stairs runs the length of the grooves with interpretive panels along it, and the whole visit is twenty minutes unless you are a geologist, in which case clear the afternoon.

It sits a short ride north of the island’s main dock area, adjacent to Kelleys Island State Park. Most people pair it with the park, which has a campground, a sand swimming beach on the north shore, and trails through the island’s alvar and woodland.

Also on the island: Inscription Rock, a limestone slab near the south shore carved with Native American pictographs, now badly weathered but still legible in raking light.

Getting there

Kelleys Island is in the western basin of Lake Erie, north of Marblehead. Ferry service runs from Marblehead and carries both passengers and vehicles; the crossing is short. Schedules are seasonal and reduce sharply after October — winter service depends on ice.

Most visitors leave the car on the mainland and rent a golf cart or bicycle on the island. The island is roughly four square miles and the roads are slow. A car is unnecessary for a day trip and the ferry charges accordingly.

When to go

May through October. Summer weekends are busy — the ferry queues in Marblehead can be long on a July Saturday, so book vehicle passage ahead or come early. September is the sweet spot: warm water, thinner crowds, and the ferry still running full schedule.

The grooves are outdoors and unshaded. Bring water in July.

The water around it

Kelleys sits in the middle of the western basin walleye and perch fishery. Reef structure surrounds the island and smallmouth bass hold on the rock all season. Charter fleets work out of Port Clinton, Marblehead and Sandusky.

The basin is shallow and dangerous in wind — a short steep chop builds fast over six to thirty feet of water and small boats get into trouble quickly. Check the western basin marine forecast before crossing, and understand that the ferry runs in conditions your boat should not.

Ohio DNR Division of Wildlife sets seasons and limits; they change with the annual stock assessment.