The contiguous United States during the Cretaceous.

The Cretaceous is a geologic period and system, reaching from the end of the Jurassic Period, (145.5 ± 4 million years ago (Ma) to the beginning of the Paleocene Period, 65.5 ± 0.3 Ma. It is the youngest geological period of the Mesozoic, and at 80 million years long, the longest period of the Phanerozoic. The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras.

Cretaceous in "The Green Buffalo"[]

Joe, Jake Snow, and Clancy O'Doole were briefly transported from 1890 CE to the Cretaceous without realizing it. Before they were returned to their own time, they encountered a Triceratops which they thought was a diseased buffalo.

Cretaceous in "Hatching Season"[]

Paula Shaffer traveled back to Montana in the Cretaceous on a grant to do a field-study of hadrosaurs.