Roughly 27,000 years ago, a lava dome pushed through Tehama's former flank, becoming Lassen Peak. About 600,000 years ago, Mount Tehama started to rise in the park's southwest corner. Lava flowed over a lahar-based formation to create the lava plateau that the park sits on. Heat from the subduction of tectonic plates has fed scores of volcanoes over at least the past 30 million years, including those in the Lassen volcanic area. presents a record of sedimentation and volcanic activity in and around Lassen Volcanic National Park in Northern California. The geology of the Lassen volcanic area in the U.S.
