|Geology of the Mesozoic Era
Tectonic Cross-sections of the United States during the Jurassic
During the Jurassic Period, North America was beginning to separate from Pangaea. The numerous fault-bounded basins on the eastern edge of the continent merged to form a thinner-than-usual area of continental crust which would ultimately become the Atlantic Ocean. This elongate ocean embayment stretched along the eastern margin of the United States to the Gulf of Mexico.
Along the western margin of North America, continued subduction of the Farallon ocean plate beneath the western edge of the continent produced immense areas of deep-seated magma. As this magma cooled it formed the granite rocks of the Sierra Nevada Mountains. Deep oceanic sediments were scrapped off of the subducting oceanic crust and piled up against the continent. These sediments are represented by the Franciscan Formation of northern California.
Graphic: David K. Brezinski