The western edge of the North American continent was later pushed against the oceanic plate under the adjacent ocean. An area of great compression called a subduction zone was formed in the early-to-mid Mesozoic, which replaced the quiet, sea-covered continental margin with erupting volcanoes and uplifting mountains. A chain of volcanoes pushed through the continental crust parallel to the deep trench, fed by magma rising from the subducting oceanic plate as it entered the Earth's hot interior. Thousands of feet (hundreds of meters) of lavas erupted, pushing the ocean over to the west.