<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>
<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>
when was the last time mt lassen erupted
when was the last time mt lassen erupted
May 22 , 1915
May 22 , 1915