When the Ohio River is low, a 386-million-year-old fossil coral reef lies bare across acres of riverbed at Clarksville, Indiana, one of the largest naturally exposed Devonian reefs anywhere. You walk on it. Late summer and autumn give the best exposure. LOOK ONLY; it is a state park and a national wildlife conservation area.
Devonian coral reef · Devonian, ~387 mya
This ground is protected. Photograph it, record it, leave it where it lies. On US federal land the Paleontological Resources Preservation Act 2009 makes collecting vertebrate fossils an offence, and penalties are real.
Other places on the map within a couple of hours.
