Geology and History

Mount Shasta is located in the Cascade Range in northern California about 65 km (40 mi) south of the Oregon-California border. One of the largest and highest (14,162 ft) of the Cascade volcanoes, the compound stratovolcano is located near the southern end of the range that terminates near Lassen Peak.

Mount Shasta erupts episodically with ten or more eruptions occurring in short (500-2,000 year) time periods separated by long intervals (3,000-5,000 years) with few or no eruptions. Evidence suggests that magma most recently erupted at the surface about 3,200 years ago.

The deposits of an exceptionally large debris avalanche extend from the base of Mount Shasta volcano northward across the floor of Shasta Valley in northern California.

The next eruption at Mount Shasta would likely involve weeks to months of precursory earthquakes and ground deformation followed by a series of steam explosions blasting a deep crater at the summit of the volcano.

Shastina is a large subsidiary cone that rises to 3,758 m (12,330 ft) and lies on the flank of Mount Shasta, 3 km (1.8 mi) west of the volcano's summit.

Black Butte is a group of overlapping dacite domes about 13 km (8 mi) west of Mount Shasta.

Hotlum cone forms the summit and the north and northwestern slopes of Mount Shasta.

Hundreds of small hills, called hummocks, extend from the base of Mount Shasta at least 45 km (27 mi) NNW across the floor of Shasta Valley. The hummocky landslide deposit was emplaced between 380,000 and 300,000 years ago during a massive debris avalanche that is not believed to be associated with volcanic activity.