St. Anthony Rock is one of several "sea stacks" I n the Mackinac area. It is made of Mackinac breccia, a type of stone formed 350 million years ago when the roofs of deep caves collapsed into stacks of fragmented rocks. Calcium Carbonate in circulating groundwater cemented the stacks of limestone, dolomite and chert into a much harder formations than the surrounding unbroken limestone. Much later, Glaciers covered this area and when they began melting about 12,000 yrs ago the wave action in the Great Lake eroded the soft adjacent stone, leaving St Anthony Rock exposed. Sometimes its call it Goudreau Rock, but it is best known as St Anthony Rock! No one is sure where the name St Anthony came from!
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