Western Interior Seaway

The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea that existed roughly over the present-day Great Plains of North America, splitting the continent into two landmasses, i.e. Laramidia to the west and Appalachia to the east. The ancient sea, which existed for 34 million years from the early Late Cretaceous (100 Ma) to the earliest Paleocene (66 Ma), connected the Gulf of Mexico (then a marginal sea of the Central American Seaway) to the Arctic Ocean. At its largest extent, the seaway was 2,500 ft (760 m) deep, 600 mi (970 km) wide and over 2,000 mi (3,200 km) long.