The Gravel Point Formation is part of the Traverse Group of Devonian age. The Gravel Point Formation is a mixture of limestones and shales. The outcrops of these rocks are restricted to the Little Traverse Bay area near Petoskey. The Gravel Point Formation is only part of the Devonian in Michigan. Devonian age rocks form the bedrock for much of the northern Lower Peninsula.
Devonian rocks outcrop at less than three percent of the surface of the United States.
Michigan's average is much higher. Much of what is known about the Devonian is interpreted from the fossil record. At least seven different species of the genus Hexagonaria are found in Devonian rocks in Michigan. The Petoskey Stone family of corals are found in Iowa, Indiana, Illinois, Ohio, New York, Canada, Germany, England, and even Asia. These corals are difficult to distinguish from each other on casual inspection.