The earlier events were of a much different, cataclysmic nature, producing rock units more than
6000 ft (1800 m) thick. The type of volcanic activity that created Yucca Mountain and the surrounding area has not recurred over the approximately 10 million years since the deposits were
originally laid down and is extremely unlikely to occur within the next 1 million years (Docket No. EPA–HQ–OAR–2005–0083–0050, pp. 7–42through 7–49).