To log this cache there are 2 requirements. First, post a picture
of yourself and your GPSr with the observatory or another known
feature in the background. Second, do some research and answer one
of the following questions:
1. Standing at the Dee Wright Observatory Memorial, what is the
direction (or bearing) to at least three of the cinder cones of
quaternary age?
2. How many cinder cones do you observe?
3. name two peaks visible from the observatory that are in excess
of 10,000 ft. Please include any additional information you learned
from the interpretive trail. Enjoy the views!
A barrier free access trail takes visitors to an interpretive
court, offering information on the history of the structure built
in the 1930s by the Civilian Conservation Corp. The half-mile Lava
River Interpretive Trail takes visitors on a 30-minute walk on a
paved surface through lava flows with spectacular vistas of the
surrounding landscape.
The Three Sisters area contains several large cones –North
Sister, Middle Sister, South Sister, Broken Top and Mount Bachelor.
North Sister and Broken Top are deeply dissected and probably have
been inactive for at least 10,000 years. Middle Sister is younger
than North Sister, and was active in the late Pleistocene but not
postglacial time. South Sister is the least dissected; its basaltic
andesite summit cone has a well preserved crater. Most of South
Sister predates late Wisconsin glaciation and is therefore older
than 25,000 years; however, eruptions of rhyolite from flank vents
have occurred as recently as 2000 years ago.
The following landmarks are seen proceeding clockwise from true
north in azimuthal degrees: -- 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.
