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Lassen Peak, also known as Mount Lassen, is the southernmost active volcano in the Cascade Range. Located in the Shasta Cascade region of Northern California, Lassen rises 2,000 ft (600 m) above the surrounding terrain and has a volume of 0.5 cu mi (2 km3), 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 that was at least 1,000 ft (300 m) 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 200 mi (300 km) 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 Shasta County, California, to preserve the devastated areas as they were, for future observation and study, and to preserve the nearby volcanic features. Unlike most lava domes, Lassen Peak is topped by craters. A set of these craters exists around the summit of Lassen Peak, although two of them have been covered up by solidified lava and sulfur deposits. Lassen Peak is the largest of a group of more than 30 volcanoes that have erupted over the past 300,000 years in the Lassen Peak volcanic area.