The Glacial Grooves State Memorial on Kelleys Island covers three and one-half acres and has been administered by the Ohio Historical Society since 1932. These immense grooves are geologically significant. About 35,000 years ago, when the climate was much cooler and wetter, a great continental glacier flowed from Canada into northern Ohio. After the climate warmed and the ice melted about 10,000 years ago, the island retained these huge glacial grooves, carved into the limestone bedrock by the advancing glacier. Because of their size and easy accessibility, they are the most famous glacial grooves in the world. Since their discovery more than a century ago, they have fascinated students, vacationers, and scientists. Geologists have studied them for many years to determine exactly how the glacier carved them, and although several theories have been proposed, no entirely satisfactory explanation has been found.