In the Cretaceous, a shallow seaway spread into the interior of North America from the Gulf of Mexico in the south into Utah and later to the Arctic Ocean in the far north.Davis and Pollock (2003). Geology of Bryce Canyon National Park, page 45 Geologists call this shallow sea the Cretaceous Seaway or Western Interior Seaway. The seaway divided North America into two halves: an eastern portion dominated by the already ancient Appalachian Mountains and a western part composed primarily of the still growing Sevier Mountains; formed from shallow thrust faulting caused by the Sevier orogeny.Davis and Pollock (2003). Geology of Bryce Canyon National Park, page 55 As the shoreline moved back and forth, the Bryce area alternated from being part of the Sevier landmass to being under the Cretaceous Seaway. Alternating layers of nonmarine, intertidal, and marine sediments lay on top of each other as a result.
