Calvin crater

Calvin is an impact crater located in Calvin Township, Cass County, in the U.S. state of Michigan. It was discovered in 1987 by Randall Milstein of the Michigan Geological Survey while examining data from about 100 test wells drilled in the area.^[1]

Calvin crater
Calvin Township, Michigan
Impact crater/structure
Confidence	Confirmed
Diameter	8.5 kilometres (5.3 mi)
Age	450 ± 10 Ma
Exposed	No
Drilled	Yes
Location
Coordinates	41.83°N 85.95°W / 41.83; -85.95
Country	US
State	Michigan

It is 8.5 kilometres (5.3 mi) in diameter and the age is estimated to be 450 ± 10 million years (Ordovician).^[2] The crater is not exposed to the surface. It lies about 100 to 400 feet (30–120 m) below today's ground level.^[1]