Tectonic Cross-sections of the United States during the Cretaceous

During the Cretaceous Period, North America was fully separated from Africa. The finger-like Atlantic Ocean was now opening wide and basaltic oceanic crust formed beneath the deepening oceanic waters.

Along the western margin of the United States the Farallon ocean plate continued to move beneath western North America and persisted in producing magmatic intrusion that formed the Sierra Nevada Mountains.

Graphic: David K. Brezinski