Lassen Volcanic National Park is a United States National Park in northeastern California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The dominant feature of the park is Lassen Peak

Lassen Peak

Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...

; the largest plug dome

Lava dome

|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...

 volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 in the world and the southern-most volcano in the Cascade Range

Cascade Range

The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...

. Lassen Volcanic National Park started as two separate national monuments

U.S. National Monument

A National Monument in the United States is a protected area that is similar to a National Park except that the President of the United States can quickly declare an area of the United States to be a National Monument without the approval of Congress. National monuments receive less funding and...

 designated by President Theodore Roosevelt

Theodore Roosevelt

Theodore "Teddy" Roosevelt was the 26th President of the United States . He is noted for his exuberant personality, range of interests and achievements, and his leadership of the Progressive Movement, as well as his "cowboy" persona and robust masculinity...

 in 1907: Cinder Cone National Monument and Lassen Peak National Monument.

The source of heat for volcanism in the Lassen area is subduction

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 off the Northern California

Northern California

Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

 coast of the Gorda Plate

Gorda Plate

The Gorda Plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon Plate. It is sometimes referred to as simply the southernmost portion of the neighboring Juan de Fuca Plate, another Farallon remnant.Unlike most tectonic...

 diving below the North American Plate

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

.