Mount Shasta, rising some 3,050 meters (10,000 feet) above its base, is one of the great active volcanoes in North America and a dominant feature of the Northern California landscape. Its last eruption probably occurred in 1786.

It is a composite volcano and, though it has been in existence throughout the Pleistocene, much of the mountain is of recent origin. The earliest Pleistocene lavas are basaltic andesite, the more recent, pyroxene andesite and some dacite. In relatively recent times two fissures have formed on the volcano, the one trending north-south includes a series of domes and cinder cones with associated lava flows; Gray and McKenzie Buttes are domes of this series, Red and Signal Buttes, cinder cones. Everitt, a shield volcano near the base, is the source of a basaltic andesite flow which can be traced some 65 kilometers (40 miles) southwestward down the Sacramento Valley.

The second fissure, trending east-west, is perhaps more recent and gave rise to Shastina, the satellitic shield cone on the western flank. This cone may have been formed as recently as 200 to 250 years ago.

Flows in Whitney and Bolam canyons, the former originating from a vent in the terminal moraine of the glacier, have almost perfectly preserved surfaces. Moraines are exposed beneath these flows.

The latest eruptions appear to have been from the main cone, the final one covering the upper part of the mountain with a thin layer of brown pumice. The summit crater is filled with a snowfield some 180 meters (600 feet) across, with an acid hot spring at the margin. Water temperature ranges between 75-85°C. (166-184°F.).

Five active glaciers, covering perhaps 520 hectares (2 square miles) are found on the north and east slopes of the summit. They are retreating: Konwaki-ton Glacier was 8 kilometers (5 miles) long in 1895, today it is some 370 meters (1,200 feet) long. In the late Pleistocene the glaciers covered the mountain and extended to the valley floor to the west and the margin of the Modoc Plateau to the east. Much of the glacial evidence has been covered by later volcanic activity, though cirques, moraines, etc., can be observed.

Vegetation is varied and includes mixed conifer, montane chaparral, Shasta fir forest, whitebark pine woodland, and alpine tundra communities. Over 600 plant species have been collected here.

There is an abundance of animal life including the uncommon marten, Martes americana, fisher, Martes pennanti, and wolverine, Gulo luscus.

Integrity: Portions of the area have been logged and grazed, and there are three active cinder pits. A highway leads to the ski resort area on the southwestern slope. Part of the area has been proposed as a Wilderness Area.

Use: Research, educational, recreational.

Ref: Hinds, Norman, 1952. Evolution of the California Landscape. California Division of Mines Bulletin No. 158, p. 122 ff., San Francisco, California. Cooke, W. B., 1940. A Flora of Mount Shasta. Am. Midi. Nat. Vol. 31, p. 497-572.
Cooke, W. B., 1972. H. E. Brown and the Plants of the "North Side of Mount Shasta." Madrono Vol. 21 No. 7, p. 487-489. 

February 1975

Siskiyou
Inventory of California Natural Areas
Revision © 2005 Steven Louis Hartman