steaming sulphur vents, splattering mud pots and boiling springs
Excellent little known National Park.
Don't pass up this park while traveling through Northern California. It is a hidden gem. This is a wonderful place to visit and there are a lot of hiking options. Take your time and really explore the area.
Lassen was a volcano and erupted around 1914 or so. Lassen Peak awoke from a 27000 year long slumber when it was shaken by a steam explosion. This explosion was the most powerful in a series of eruptions from 1914 through 1917.