DESCRIPTION:
California Volcanoes and Volcanics

Holocene volcanism in the Cascades extends from the Garibaldi Volcanic Belt in southern British Columbia to the Lassen volcanic complex in northern California. Pronounced differences in the nature of volcanism occur along the arc. In Washington there are five, generally large, widely spaced stratovolcanoes, with only one ( Mount Adams) having significant nearly basaltic volcanics. In marked contrast, Oregon has six generally smaller stratovolcanoes, but the entire state is traversed by a 40-50-kilometer-wide band of basaltic to andesitic lava shields, cinder cones, and smaller stratovolcanoes that the "Cascade" cones rise above. South of Crater Lake, the Cascade arc bends perceptibly toward the southeast, and continues along this trend to Lassen Peak. Both Lassen and Shasta are associated with eastward halos of mafic shields and lava fields which, near Shasta, culminate in the huge shield volcano of Medicine Lake.

The Cascade Range has been an active arc for about 36 million years as a result of plate convergence. Volcanic rocks between 55 and 42 million years ago occur in the Cascades, but are probably related to a rather diffuse volcanic episode that created the Challis arc extending southeastward from northern to northwest Wyoming. Convergence between the North American and Juan de Fuca plates continues at about 4 centimeters per year in the direction of North-50-degrees-East, a slowing of 2-3 centimeters per year since 7 million years ago. According to most interpretations, volcanism in the Cascades has been discontinuous in time and space, with the most recent episode of activity beginning about 5 million years ago and resulting in more than 3000 vents.

In Oregon, the young terrane is commonly called the High Cascades and the old terrane the Western Cascades, terms that reflect present physiography and geography. The terms are not useful in Washington, where young vents are scattered across the dominantly middle Miocene and older terrane. ...

In Washington and Oregon, a striking contrast has existed for the past 5 million years in the style of volcanism in the Cascades relative to geography. North of Mount Rainier, young volcanism is concentrated in only a few isolated andesitic and dacitic composite cones (notably Glacier Peak, Mount Baker, and the volcanoes of the Garibaldi belt in British Columbia), whereas south of Mount Hood moderate-sized andesitic and dacitic composite cones are relatively unimportant features of a landscape dominated by small andesite and basalt vents. The area between Mounts Rainier and Hood is transitional; large andesite and dacite composite cones ( Rainier, Adams, St. Helens, Hood, and the extinct Goat Rocks volcano) occur together with fields and scattered vents of olivine basalt ( Indian Heaven, Simcoe Mountains, and the King Mountain fissure zone south of Mount Adams. ...

The southern Washington Cascades are seismically active. Most earthquakes occur along the 100-kilometer-long, north-northwest trending St. Helens seismic zone, where most focal mechanisms show dextral slip parallel to the trend of the zone and consistent with the direction of plate convergence. Other crustal earthquakes concentrate just west of Mount Rainier and in the Portland (Oregon) area. Few earthquakes occur north of Mount Rainier or south of Mount Hood.

From tomography, Rasmussen and Humphreys (1988) interpret the subducted Juan de Fuca plate as a quasi-planar feature dipping about 65 degrees to about 300 kilometers under the southern Washington Cascades. The plate is poorly defined seismically, however, owing to a lack of earthquakes within it. Guffanti and Weaver (1988) show that the present volcanic front of the Washington Cascades, defined by the westernmost young vents, parallels the curved trend of the subducting plate reflected by the 60 kilometer-depth contour. The front trends northwest in northern Washington -- where Glacier Peak, Mount Baker, and the volcanoes of southern British Columbia occur along a virtually straight line -- and northeast in southern Washington. A 90-kilometer gap free of young volcanoes between Mount Rainier and Glacier Peak is landward of that part of the subducting plate with the least average dip to a depth of 60 kilometers. South of Portland, the volcanic front is offset 50 kilometers eastward and extends southward into California, probably still parallel to the trend of the convergent margin.

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• Volcano Name; Latitude; Longitude; Elevation; Volcano Type; and Type of evidence for Holocene activity
• Amboy 34.55 N, 115.78 W, 288 meters, Cinder cone, Holocene
• Big Cave 40.955 N, 121.365 W, 1259 meters, Shield volcano, Holocene?
• Brushy Butte 41.178 N, 121.443 W, 1174 meters, Shield volcano, Holocene?
• Clear Lake 38.97 N, 122.77 W, 1439 meters, Volcanic field, Holocene
• Coso Volcanic Field 36.03 N, 117.82 W, 2400 meters, Lava domes, Holocene?
• Eagle Lake Field 40.63 N, 120.83 W, 1652 meters, Fissure vents, Holocene?
• Golden Trout Creek 36.358 N, 118.32 W, 2886 meters, Volcanic field, Tephrochronology
• Inyo Craters 37.692 N, 119.02 W, 2629 meters, Lava domes, Radiocarbon
• Lassen Volcanic Center 40.492 N, 121.508 W, 3187 meters, Stratovolcano, Historical
• Lavic Lake 34.75 N, 116.625 W, 1495 meters, Volcanic field, Holocene
• Long Valley 37.70 N, 118.87 W, 3390 meters, Caldera, Pleistocene-Fumarolic
• Medicine Lake 41.58 N, 121.57 W, 2412 meters, Shield volcano, Radiocarbon
• Mono Craters 37.88 N, 119.00 W, 2796 meters, Lava domes, Radiocarbon
• Mono Lake Volcanic Field 38.00 N, 119.03 W, 2121 meters, Cinder cones, Tephrochronology
• Potato Butte 40.63 N, 121.43 W, 1532 meters, Shield volcanoes, Holocene?
• Red Cones 37.58 N, 119.05 W, 2748 meters, Cinder cones, Holocene
• Shasta 41.42 N, 122.20 W, 4317 meters, Stratovolcano, Historical
• Tumble Buttes 40.68 N, 121.55 W, 2191 meters, Cinder cones, Holocene?
• Twin Buttes 40.78 N, 121.60 W, 1631 meters, Cinder cones, Holocene?
• Ubehebe Craters 37.02 N, 117.45 W, 752 meters, Maars, Holocene

Lassen Vicinity:

• Volcano or Feature Name; Location; Volcano type, age and other comments

• Bear Wallow Butte: Lassen vicinity, approximately 9 kilomters northwest of Red Lake Mountain. Bear Wallow Butte is cinder cone, the southernmost of a chain of vents called the Tumble Buttes.

• Blacks Mountain; Lassen vicinity, 25 kilometers east of Hat Creek Valley. Blacks Mountain is the most conspicuous of a number of andesitic shield volcanoes. Blacks Mountain is 1 to 2 million years old.

• Blue Ridge: Lassen vicinity, near Mineral. Blue Ridge is a 300-meter-thick rhyolite lava flow covering 80 square kilometers on the west flank of the Maidu volcanoic center, and is probably the largest rhyolite flow in the Cascade Range.

• Brokeoff Mountain: Lassen Volcanic National Park. Erosional remnant of Brokeoff volcano.

• Brokeoff Volcano: Lassen Volcanic National Park. Initial volcanic center, approximately 600,000 years old. The major erosional remnants, Brokeoff Mountain, Mount Diller, Mount Conard, and Diamond Peak, enclose a central depression that marks the position of Brokeoff volcano. Brokeoff volcano was about 3,350 meters high with a basal diameter of about 12 kilometers, and a volume of 80 cubic kilometers.

• Burney Mountain: Thousand Lakes Wilderness area, Lassen vicinity. Burney Mountain is a large dacite dome cluster. Five separate domes are bulilt one on top of another. Burney Mountain has been dated at 230,000 years.

• Bumpass Mountain: Lassen Volcanic National Park. Prominant dome.

• Butt Mountain: Lassen vicinity, a remnant of the Yana Volcanic Center.

• Chaos Crags: Lassen Volcanic National Park. Prominant domes, 1,100 to 1,000 years ago.

• Chaos Jumbles: Lassen Volcanic National Park. Chaos Crags domes formed 1,100 to 1,000 years ago. Approximately 700 years later one of the domes collapsed in a series of three cold rockfall-avalanches, creating Chaos Jumbles.

• Christie Hill: in Maidu Volcanic Center Lassen vicinity. Christie Hill is a dacite lava dome.

• Cinder Butte: located at the north end of Hat Creek Valley Lassen vicinity. Cinder Butte is a basaltic andesite shield volcano, and is slightly older than the Hat Creek Basalt.

• Cinder Cone: Lassen Volcanic National Park. Cinder Cone eruptive consists of four basaltic andesite lava flows, a complex vent cone, and an ash blanket covering 200 to 300 square kilometers. Two lava flows erupted before the ash blanket and two followed the ash blanket. All of these erupted over a short time interval, approximately 425 years ago (Carbon-14).

• Clover Mountain: Lassen vicinity, a remnant of the Snow Mountain Volcanic Center.

• Cold Creek Butte: Lassen vicinity. Cold Creek Butte is a basaltic cinder cone, approximately 20,000 years old.

• Diamond Peak: Lassen Volcanic National Park. Erosional remnant of Brokeoff volcano.

• Dittmar Volcanic Center: in the southeastern part of Lassen Volcanic National Park. It had a diameter of approximately 20 kilometers and was centered in the upper Warner Creek Valley, includes Kelly Mountain, Mount Hoffman, Pilot Mountain, and Saddle Mountain. Stratigraphy suggests that the Dittmar volcanic center was active from approximately 2.5 to 1 million years ago.

• Doe Mountain: in Maidu Volcanic Center Lassen vicinity. Doe Mountain is a dacite lava dome.

• Freaner Peak: Thousand Lakes Wilderness area, Lassen vicinity. Freaner Peak is an olivine andesite shield volcano.

• Green Mountain: Lassen vicinity, a remnant of the Snow Mountain Volcanic Center.

• Hampton Butte: in Maidu Volcanic Center Lassen vicinity. Hamption Butte is a hydrothermally altered and deeply eroded andesitic stratovolcano

• Hat Creek Basalt: Lassen vicinity. Stratigraphic evidence suggest that the Hat Creek Basalt is approximately 15,000 years old. It was a very fluid lava that flowed in lava tubes. A row of spatter cones marks the location of the fissure.

• Humboldt Peak: Lassen vicinity, a remnant of the Yana Volcanic Center.

• Kelly Mountain: in Dittmar Volcanic Center Lassen vicinity. Kelly Mountain is a deeply eroded andesitic stratovolcano.

• Lassen Peak: a dacite dome, erupting approximately 25,000 years ago. Lassen Peak's last eruption was in 1914-1917.

• Lassen Volcanic Center: The Lassen volcanic center in Lassen Volcanic National Park consists of an andesitic stratovolcano, a dacite dome field, and peripheral small andesitic shield volcanoes. The last eruption was in 1917.

• Latour Butte: located north of Viola, Lassen vicinity. Latour Butte is an andesitic lava cone, probably 1-2 million years old.

• Logan Mountain: Lassen vicinity. Logan Mountain is an andesitic lava cone.

• Magee Volcano: in the Thousand Lakes Wilderness area Lassen vicinity. The Magee Volcano is a deeply eroded andesitic composite cone. The Magee Volcano is 1 to 2 million years old.

• Maidu Volcanic Center: located in the area around Battle Creek Meadows near the town of Mineral, Lassen vicinity. Maidu Volcanic Center is at least 25 kilometers in diameter and includes Blue Ridge, Christie Hill, Doe Mountain, Hampton Butte, Morgan Mountain, Red Rock Mountain, Rocky Peak, and Turner Mountain. The Maidu volcanic center was active from approximately 2 million to 700,000 years ago.

• Morgan Mountain: in Maidu Volcanic Center, Lassen vicinity. A dacite lava dome.

• Mount Conard: Lassen Volcanic National Park. Erosional remnant of Brokeoff volcano.

• Mount Diller: Lassen Volcanic National Park. Erosional remnant of Brokeoff volcano.

• Mount Harkness: southeast corner of Lassen Volcanic National Park. Mount Harkness is an andesitic shield volcano with post-glacial cinder cone summit.

• Mount Helen: Lassen Volcanic National Park. Prominant dome.

• Mount Hoffman: in Dittmar Volcanic Center. Lassen vicinity. Mount Hoffman is a deeply eroded andesitic stratovolcano.

• Pilot Mountain: in Dittmar Volcanic Center, Lassen vicinity. Pilot Mountain is a deeply eroded andesitic stratovolcano.

• Prospect Peak: along northern boundary of Lassen Volcanic National Park. Prospect Peak is an andesitic shield volcano with a cinder cone at its summit. Prospect Peak is younger than West Prospect Peak, although both are less than a few hundred thousand years old.

• Reading Peak: Lassen Volcanic National Park. Prominant dome.

• Red Lake Mountain: Lassen vicinity. Red Lake Mountain is a large cinder cone surrounded by lava flows erupted from its base.

• Red Rock Mountain: in Maidu Volcanic Center Lassen vicinity. Red Rock Mountain is a dacite lava dome.

• Rocky Peak: in Maidu Volcanic Center Lassen vicinity. Rocky Peak is a dacite lava dome.

• Ruffa Ridge: a remnant of the Yana Volcanic Center, Lassen vicinity.

• Saddle Mountain: in Dittmar Volcanic Center Lassen vicinity. Saddle Mountain is a deeply eroded andesitic stratovolcano.

• Sifford Mountain: located on the southern boundary of Lassen Volcanic National Park. Sifford Mountain is a basaltic to andesitic shield volcano with small cinder cone at its summit.

• Ski Heil Peak: Lassen Volcanic National Park. Prominant dome.

• Snow Mountain: Lassen vicinity, a remnant of the Snow Mountain Volcanic Center.

• Snow Mountain Volcanic Center: 16 kilometers southwest of Burney, Lassen vicinity. Two K-Ar dates suggest that the Snow Mountain volcanic center was active from approximately 2 to 1 million years ago. Includes Snow Mountain, Green Mountain, and Clover Mountain. The center is deeply eroded, and the hydrothermally altered core of the andesitic stratovolcano is exposed in the canyon walls of creeks draining the area.

• Subway Cave: a piece of a lava tube, in the Hat Creek Basalt, Lassen vicinity.

• Sugarloaf: Lassen vicinity north of "Old Station". Sugarloaf is an impressive andesitic lava cone, probably 20 to 30 thousand years old.

• Table Mountain: just north of Lassen Volcanic National Park. Table Mountain is an andesitic shield volcano, probably formed about 1 to 2 million years ago.

• Tumble Buttes: northwest of Red Lake Mountain Lassen vicinity. Tumble Buttes includes the cinder cone Bear Wallow Butte.

• Turner Mountain: in Maidu Volcanic Center Lassen vicinity. Turner Mountain is a hydrothermally altered and deeply eroded andesitic stratovolcano.

• West Prospect Peak: located along northern boundary of Lassen Volcanic National Park. West Prospect Peak is a lava cone of basaltic andesite to andesite. Prospect Peak is younger than West Prospect Peak, although both are less than a few hundred thousand years old.

• Yana Volcanic Center: 20 kilometers southwest of Chester, Lassen vicinity. Butt Mountain, Ruffa Ridge, and Humboldt Peak are the major remnants of a deeply eroded andesitic stratovolcano that was 15-20 kilometers in diameter. The Yana volcanic center was active approximately 3 to 2 million years ago.

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