Geology

The Apostle Islands are remnants of sedimentary rocks deposited in the Lake Superior basin more than 600 million years ago. The islands have survived the crushing action of four glaciers during the past 100,000 years.

When Madeline Island reappeared from under the last glacier, about 15,000 years ago, Big Bay Lagoon was a large, shallow, open bay. Shoreline currents and waves soon built a barrier beach across the middle of Big Bay and later formed another barrier beach across the mouth of the bay. Big Bay Lagoon, thus, lies between two barrier beaches.

The 440-acre sand spit and bog area has been designated as a Wisconsin State Natural Area. This outstanding geological and scenic area is being preserved by the State of Wisconsin and the Department of Natural Resources for the enjoyment of present and future generations.