Lassen Peak, commonly referred to as Mount Lassen, is the southernmost active volcano in the Cascade Range. Located in the Shasta Cascade region of Northern California, Lassen rises 3500ft above the surrounding terrain and has a volume of 0.5cumi, making it one of the largest lava domes on Earth.
It was created on the destroyed northeastern flank of now-gone Mount Tehama, a stratovolcano at least 1000ft higher than Lassen Peak. It is part of the Cascade Volcanic Arc, which stretches from southwestern British Columbia to northern California.
On May 22, 1915, a powerful explosive eruption at Lassen Peak devastated nearby areas, and spread volcanic ash as far as 200mi to the east. This explosion was the most powerful in a series of eruptions from 1914 through 1917. Lassen Peak and Mount St. Helens were the only two volcanoes in the contiguous United States to erupt during the 20th century. Lassen Volcanic National Park was created in Tehama County, California, to preserve the devastated areas as they were, for future observation and study, and to preserve the nearby volcanic features.