America’s Emerald Isle

In a process that played out over thousands of years, a retreating ice sheet carved, scoured, and shaped the landscape of the present-day Great Lakes. In northern Lake Michigan, this sculpting left distinct ridges and valleys running north-to-south along the lake floor. Some parts of those ridges, made of erosion-resistant rock, have remained above the waves of the big lake, forming the Beaver Archipelago. …