Rising just north of the Sierra Nevada Range, Lassen Peak (10,461 feet) and its cohort of volcanic domes represent the southern end of the Cascade Volcanic Arc that extends from British Columbia to northern California. All of the well known volcanoes along this arc, and those that preceded them, have formed along a subduction zone where remnants of the Farallon Plate dip below the North American Plate.
Protected within a National Park since 1916, the Lassen Peak volcanic field contains 30 peaks in addition to smaller domes and cones. Lassen Peak, the centerpiece of the Park, formed 27,000 years ago on the northeast flank of the Mt. Tehama caldera; the latter volcano, at least 1000 feet taller than Lassen, exploded and collapsed about 350,000 years ago. Lassen, itself, last erupted in 1915 but remains active (as revealed by numerous fumaroles, mud pots and hot springs on its slopes).
Named for Peter Lassen, a local guide and blacksmith during the early 19th Century, Lassen Peak, like the other large volcanoes of the Cascade Range, is an ultra-prominent peak. Rising as it does at the northeast end of the Sacramento Valley, it receives upslope flow from all directions and has the highest average annual snowfall (660 inches) of any location in California. Most streams within the National Park drain toward the Sacramento River via the Pitt River that runs north of the Park, the Feather River of the northern Sierra or Battle Creek that drops west from the Park; the eastern edge of the Park lies on the rim of the Great Basin. Mt. Shasta looms NNE of Lassen Peak while Brokeoff Mountain (9235 feet), the second highest summit in the Park, rises to its southwest, just across the Tehama Caldera.
