Tanis, a private paleontological site in southwestern North Dakota within the Hell Creek Formation, may preserve the immediate aftermath of the Chicxulub impact that is widely linked to the end-Cretaceous mass extinction about 66 million years ago. First found in 2008 and excavated systematically from 2012, the site has been interpreted as an ancient river point bar overwhelmed when impact-driven seismic waves triggered seiche surges as microtektites fell. Reported finds include three-dimensionally preserved fish with microtektites in their gills and mixed freshwater, marine, and terrestrial remains, suggesting a single catastrophic episode. Although some scientists urge further scrutiny, Tanis is closely watched for its potential to capture the extinction event almost as it happened.