Discover a dramatic landscape created by relatively recent rock-forming activity in the Grand Canyon in this video from NOVA. Volcanic eruptions only a million years ago created the canyon's youngest rocks. In contrast with the much older Vishnu Schist formation, this younger rock has been much more susceptible to physical change. When three-hundred-meter (thousand-foot) lava dams periodically blocked the river, they were quickly eroded away and river flow restored. This video is available in both English and Spanish audio, along with corresponding closed captions.