Wisconsin

"The boulder is a rare, large example of a pre-Cambrian era glacial erratic that experts say is likely over 2 billion years old. It was carried by glaciers from as far north as Canada and dumped on Observatory Hill along with billions of tons of other debris when ice receded from the state about 12,000 years ago. It was previously estimated to have weighed up to 70 tons, but an updated measurement shows it weighs 42 tons. It will continue to be used for educational purposes at its new site."