Lassen Peak, the world's largest plug-dome volcano, rises 2000ft over the surrounding landscape to 10,457ft above sea level. Classified as an active volcano, its most recent eruption took place in 1915 when it blew a giant cloud of smoke, steam and ash 7 miles into the atmosphere. The national park was created the following year to protect the newly formed landscape. Some areas destroyed by the blast, including the aptly named Devastated Area, northeast of the peak, are recovering impressively.

Hwy 89, the road through the park, wraps around Lassen Peak on three sides and provides access to the geothermal areas, lakes, picnic areas and hiking trails. It's only possible to drive through the park in summer, usually around June to October. There have been times when the road has been closed due to snow (as much as 40ft of it) well into July.