Belknap84_dee_wright_observatory_10-01-84_bw.jpg Dee Wright Observatory, Belknap Shield Volcano, McKenzie Pass, Oregon. USGS Photograph taken on October 1, 1984, by Lyn Topinka. [medium size] ... [large size] ... [TIF Format, 25 M] ...

0 -- Mount Jefferson:

Andesitic composite volcano

7 -- Cache Mountain:

Glaciated basaltic andesite volcano, 0.9 million years old, with late Pleistocene basalt cinder cones and lavas on summit.

11 -- Bald Peter (far horizon):

Basaltic andesite volcano, 2.1 million years old, deeply glaciated, constructed against the north end of the Green Ridge fault escarpment.

20 -- Dugout Butte (forested foreground):

Glaciated diktytaxitic basalt flows of the High Cascade platform.

30 -- Green Ridge (far horizon):

North/South fault block mountain, 20 miles long. Escarpment faces west. Lavas on crest are 5-6 million years old.

40 -- Black Butte (background), Bluegrass Butte (foreground):

Black Butte: Basaltic cinder cone located at south end of Green Ridge. Older than any of the other visible High Cascade volcanoes; well preserved form is due to lack of glaciation east of the Cascade Range. Bluegrass Butte: Glaciated basaltic andesite cinder cone. Ridge east of cone is a lateral moraine.

82 -- Black Crater (fills most of eastern sector):

Late Pleistocene basaltic andesite volcano. "Crater" is actually a glacial cirque open to the northeast.

105 - 155 -- Unnamed Cascade summit ridge:

Composed of glaciated basaltic andesite cinders, bombs, and lavas which issued from a 5-mile-long chain of cones. Probably was the site of spectacular lava fountains and eruptions of unusually large and abundant volcanic bombs during the late Pleistocene.

168 -- North Sister (elevation 10,085 feet):

Basaltic andesite composite volcano on a broad shield. Central plug and dike systems exposed by glacial erosion. At base of North Sister stand Yapoah Cone (left) and Collier Cone (right).

174 -- Middle Sister (elevation 10,045 feet):

Composite volcano supporting Collier Glacier. Predominantly olivine basalt porphyry but also contains flows of basaltic andesite, andesite, dacite, and rhyodacite. Younger than North Sister.

178 -- Summit of Little Brother and ridge west:

Basaltic composite volcano with exposed plug and dikes. Older than North Sister.

188 -- Four-in-One cinder cone (below skyline):

A ridge-cone breached in four places by andesite lava flows, 2,600 years ago. Part of a north/south alignment of 19 vents.

197 -- The Husband (on skyline, partly obscured):

Although of late Pleistocene age, it is one of the oldest and most extensively dissected volcanoes in this region. The exposed plug of basaltic andesite is 1/4-mile in diameter.

218 -- Condon Butte:

Late Pleistocene cinder cone surrounded by glaciated lava field of basaltic andesite. Nested summit craters. Knob visible at left base is an unnamed glaciated dome of rhyodacitic obsidian.

235 -- Horsepasture Mountain (far horizon):

Western Cascade peak.

256 -- Scott Mountain:

Small summit cone on broad glaciated basaltic shield.

282 -- South Belknap Cone:

Cone was formed and breached 1800 years ago, then surrounded by basaltic andesite lava from a nearby vent about 1500 years ago.

286 and 306 -- Unnamed twin steptoes (in foreground lava field):

Glaciated basaltic andesite volcanoes surrounded by lava from Little Belknap.

309 -- Belknap Crater (summit cone on skyline):

Focal point of a long-continued and complex episode of Holocene basalt and basaltic andesite volcanism. The broad shield which fills the northwest view is 5 miles in diameter; it is estimated to be 1,700 feet in maximum thickness and 1.3 cubic miles in volume. The volcano probably contains a core of cinders which interfingers with peripheral lavas and whose surface expression is the summit cone. Basaltic andesite issued from vents at the north and south bases of the cone approximately 1,500 years ago. Lava poured 12 miles to the west and ash was ejected from the northernmost of two summit craters. The main bulk of Belknap ash, which has been traced over an area exceeding 100 square miles, was ejected earlier from a larger south crater. Still earlier lavas were basaltic and moved eastward 7 miles from their vents.

321 -- Little Belknap:

A subsidiary shield volcano, built 2,900 years ago on the east flank of the larger Belknap shield.

340 -- Mount Washington (elevation 7,795 feet):

Glaciated remnant of a large basaltic andesite composite volcano. Central plug is flanked by north-south swarm of dikes in summit cone.

[Map,17K,InlineGIF]
Bend/Sisters/Santiam Pass/McKenzie Pass Area
-- Modified from: Taylor, Oregon State University, 1981, IN: USGS Circular 838

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