The Garden Peninsula is part of the western sill of limestone bedrock of the Niagara Escarpment. The other surviving portion of the sill is now Wisconsin's Door Peninsula. Parts of the limestone sill between the Door and Garden peninsulas have been eroded away by glaciers. An archipelago of islands south of the Garden Peninsula spans the gap between the two peninsulas, and hems in Green Bay, Lake Michigan's largest bay, to the west. The Garden Peninsula's line of limestone hills reaches as high as 165 feet (56 m) above the water at Burnt Bluff south of Fayette.
