Indians.org tells the story of the creation of Mackinac Island’s Arch Rock and says that even now the bravest of the Ottawa people will not walk over it. My favorite Michigan history book, Lore of the Great Turtle by Dirk Gringhuis, says that Arch Rock was the bridge over which departed souls could find their final resting place and also tells another story of its formation due to an angry father, the Sky Person Evening Star and the tears of She-who-walks-like-mist. (seriously, if you have an 8-12 year olf on your gift list, buy them this book)
Wikipedia’s Arch Rock entry takes a more scientific bent, saying that this 149′ limestone arch formed during the Nipissing post-glacial period, characterized by high Lake Huron levels following the end of the Wisconsin glaciation. Arch Rock is one of several limestone formations in Mackinac Island State Park.
The photo is from the Detroit Publishing Company collection (c. 1899) at the Library of Congress (LC-USZC2-6399 DLC). You can get a larger view at Flickr and a massive 47 MB TIFF at the Library of Congress.