The Western Interior Seaway was a location in the North America during the Cretaceous Period, when an inland sea split the land that is the United States in half.

The Cretaceous beach was possibly located in the seaway, due to the presence of Hesperornis. (Episode 1.3) Some Deinosuchus which appeared in Maidenhead presumably came through an Anomaly from the seaway. (Fire and Water)