In 1993 Coralville Lake finally overtopped its spillway, and for 28 days up to 17,000 cubic feet of water a second poured down it, wiping out the road and the campground below and scouring away 15 feet of river silt and sand. Underneath lay bedding planes of Cedar Valley limestone, a 375-million-year-old sea floor with its fossils standing out in relief. Over Labor Day weekend that year 16,000 people came in through one of the two entrances alone, and the floods of 2008 scoured it again. Pick up the brochure at the entrance and walk the gorge floor; the six-sided colonial coral Hexagonaria, the shape the entry plaza copies, is one to look for. Removing or damaging fossils is strictly prohibited and carries a fine.
Colonial corals including Hexagonaria, and other sea-floor life · Middle Devonian, ~375 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.
