Mount Tehama is an eroded andesitic stratovolcano in the Cascade Volcanic Arc and the Cascade Range in Northern California. Part of the Lassen volcanic area, its highest remaining remnant, Brokeoff Mountain, is itself the second highest peak in Lassen Volcanic National Park and connects to the park's highest point, Lassen Peak. Located on the border of Tehama County and Shasta County, Tehama's peak is the highest point in the former. The hikers that summit this mountain each year are treated to "exceptional" views of Lassen Peak, the Central Valley of California, and many of the park's other features. On clear days, Mount Shasta can also be seen in the distance.
Tehama started life some 600,000 years ago. At its peak activity, it reached approximately 3,350 meters (11,000 ft) high, with a basal diameter of approximately 12 kilometers. Volcanic activity then declined 400,000 years ago, with other volcanic lava domes forming at the edges of Mount Tehama later on, the largest and best known of which is Lassen Peak. A combination of continued hydrothermal activity and erosion, particularly by glaciers during ice ages, removed the central cone of the volcano, leaving a large caldera, the northern edge of which can still be seen.
Other remnants of Mount Tehama include Mount Conard, Pilot Pinnacle, Mount Diller, and Diamond Peak.