Susan, here's a link to the Humongous Fungus site, down in Crystal Falls, MI.
http://www.crystalfalls.org/humongou.htm
This was the original 38 acre identification, but there are other suspected sites in our area that are purported to be thousands of acres. This one is apparently constrained by surrounding roads which have isolated this particular growth. Areas that have few, or many abandoned roads, such as the Porcupine Mountain Wilderness Park, are suspected (at least by me) of having more extensive growths of this fungus.
The park, the largest State Park in Michigan, covers 91 square miles (58,240 acres), over 50 square miles of which are considered Virgin Timber. It is home to white tail deer, great numbers of coyotes, many black bear, several wolf packs, and a few cougars, which the DNR seems to refuse to recognize as being there, and quite an assortment of reptiles and amphibians. It also has one of the greatest variety of wildflowers anywhwere in the midwest. Oh, ya, it's got more than it's share of porcupines, too, but that is NOT how the park got it's name.
http://www.exploringthenorth.com/porkiesum/summer.html
OK, that's my plug for the UP's Chamber of Commerce. Come on up, now, eh?
Al