https://www.nps.gov/lavo/index.htm
Established 8/9/1916 Size 106,372.36 acres (430.5 km2) Lassen Peak, the largest plug dome volcano in the world, is joined by all three other types of volcanoes in this park: shield, cinder dome, and composite. Other than the volcano, which last erupted in 1915, the park has hydrothermal areas, including fumaroles, boiling pools, and steaming ground, heated by molten rock under the peak.[45]
Lassen Volcanic National Park is an American national park in northeastern California. The dominant feature of the park is Lassen Peak, the largest plug dome volcano in the world and the southernmost volcano in the Cascade Range.[3] Lassen Volcanic National Park is one of the few areas in the world where all four types of volcano can be found—plug dome, shield, cinder cone, and stratovolcano.[4]
The source of heat for the volcanism in the Lassen area is subduction of the Gorda Plate diving below the North American Plate off the Northern California coast.[5] The area surrounding Lassen Peak is still active with boiling mud pots, fumaroles, and hot springs.[6]
Lassen Volcanic National Park started as two separate national monuments designated by President Theodore Roosevelt in 1907: Cinder Cone National Monument and Lassen Peak National Monument.[7] Starting in May 1914 and lasting until 1917, a series of minor to major eruptions occurred on Lassen. Because of the eruptive activity and the area's stark volcanic beauty, Lassen Peak, Cinder Cone, and the area surrounding were established as a National Park on August 9, 1916.