<Tr> <Th_colspan="2"> Climbing </Th> </Tr> <Tr> <Th> Easiest route </Th> <Td> Hike </Td> </Tr> <P> Lassen Peak, commonly referred to as Mount Lassen, is the southernmost active volcano in the Cascade Range of the Western United States . Located in the Shasta Cascade region of Northern California, Lassen stands 3,500 ft (1,100 m) above the surrounding terrain and has a volume of 0.5 cu mi (2 km), making it one of the largest lava domes on Earth . It arose on the destroyed northeastern flank of now - gone Mount Tehama, a stratovolcano 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 . </P> <P> 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 Tehama County, California, to preserve the devastated areas as they were, for future observation and study, and to preserve the nearby volcanic features . </P>

Which california mountain was made by volcanic eruptions