It is considered to have lived about 11,000 to 13,000 years ago. Radiocarbon dating will more accurately date the bones to within a century.
Early study shows that the mastodon carcass was harvested by primitive hunters or scavengers. They likely stored the animal's meat at the bottom of a pond that no longer exists.
More than 75 bones, or about 70 percent of the animal, were found preserved in fine-grain pond sediment. They will be furthered studied at the University of Michigan Museum of Paleontology.
About 300 mastodons have been found in Michigan, but only about 10 are as intact.
"I think the last time a mastodon this complete was found in Michigan was in the 1940s," Daniel Fisher, director of the museum and leader of the dig, said in a release. "As I recall, she was about 80 percent complete."