Western Cascades
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The Western Cascades is a region of the
U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...
of
Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...
between the
Willamette Valley The Willamette Valley ( ) is a long valley in Oregon, in the Pacific Northwest region of the United States. The Willamette River flows the entire length of the valley and is surrounded by mountains on three sides: the Cascade Range to the eas ...
and the High Cascades. Deposits of Western Cascades age are also found in adjacent southwest
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
state. The range contains many extinct shield
volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...
es, cinder cones and lava flows. The range is highly eroded and heavily forested.


Geology

The region was volcanically active from approximately 35 to 17 million years ago. The province is characterized as an older, deeply eroded volcanic range lying west of the more recent snow-covered High Cascade Range. They range in elevation from on the western margin to on the eastern margin. The Western Cascades began to form 40 million years ago with eruptions from a chain of volcanoes near the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
shoreline. As the regional angle of subduction steepened, volcanic activity gradually shifted to the east in the
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
and
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 The Western Cascades are made up almost entirely of slightly deformed and partly altered volcanic flows and pyroclastic rocks which range in age from late
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
to late
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
. These rocks have been heavily dissected by erosion and the only evidence remaining of the many volcanoes from which they were erupted are occasional remnants of volcanic necks or plugs which mark former vents. There are also minor Pliocene to
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
intracanyon lavas derived from the High Cascades or rare local vents. From youngest to oldest, the Western Cascade Range consists of four main units: # 0- to 4-million-year-old intracanyon
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
and
basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Amer ...
flows from the High Cascade Range. # 4- to 9-million-year-old basalt and basaltic andesite flows with lesser amounts of andesite and
dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite ...
. These rocks which cap the highest Western Cascade ridges were erupted prior to uplift and faulting along the east margin of the Western Cascade Range. This unit is compositionally identical to unit 1 and other rocks of the High Cascade Range, and therefore was probably erupted from vents in and adjacent to the High Cascades. # 9- to 18-million-year-old basalt, basaltic andesite, and andesite lavas with lesser amounts of dacite tuffs and lavas. # 18- to 40-million-year-old silicic tuffs and lavas. Units 3 and 4 were erupted from many vents west of known High Cascade volcanic centers, although some of these older vents may be buried beneath the High Cascade Range.


Wild life

Wildlife species richness is not as high in the West Cascades as it is in other temperate conifer forests, however the ecoregion is notable for comparatively high amphibian endemism. A diverse range of plant species including numerous endemics are found in the ecoregion but are especially concentrated near Mount Rainier in Washington and the Columbia River Gorge. A number of amphibian targets are either West Cascade endemics or have a limited distribution. The Cascades torrent salamander
Rhyacotriton cascadae The Cascade torrent salamander (''Rhyacotriton cascadae'') is a species of salamander in the family Rhyacotritonidae. It is endemic to the Pacific Northwest in the United States where it is found from Skamania County in Washington south to Lane ...
and Larch Mountain salamander Plethodon larselli are restricted to the ecoregion, whereas Cope’s giant salamander
Dicamptodon copei Cope's giant salamander (''Dicamptodon copei'') is a species of salamander in the family Dicamptodontidae, the Pacific giant salamanders.Behler, J. L. and F. W. King. (1979) ''National Audubon Society Field Guide to Reptiles and Amphibians'', Kn ...
, Van Dyke’s salamander Plethodon vandykei, and the Cascades frog
Rana cascadae The Cascades frog (''Rana cascadae'') is a species of frog in the family Ranidae found in the Pacific Northwest, mainly in the Cascade Range and Olympic Mountains. Description Appearance The Cascades frog has a green to brown color on its ba ...
occur only in the West Cascades and Pacific Coast ecoregions. Of these, the Larch Mountain and Van Dyke’s salamanders and the Cascades frog are federal Species of Concern. Most of these amphibians are also closely associated with fast-moving, cold mountain streams.


Notable vents


See also

*
List of volcanoes in the United States A list of volcanoes in the United States and its territories. Alaska American Samoa Arizona California Colorado Hawaii / /[Https://www.sci.news/geology/puhahonu-shield-volcano-08435.html Puhahonu ...
* Types of volcanic eruptions


References

''Portions of this article include public domain text from the USFS]
Deschutes & Ochoco National Forests - Crooked River National Grassland
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Further reading

*{{cite book , last1 = Du Bray , first1 = E.A. , authorlink1 = , last2 = John , first2 = D.A. , last3 = Sherrod , first3 = D.R. , last4 = Evarts , first4 = R.C. , last5 = Conrey , first5 = R.M. , last6 = Lexa , first6 = J. , title = Geochemical database for volcanic rocks of the Western Cascades, Washington, Oregon, and California , publisher =
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
, year = 2006 , location = Reston, Virginia , page = 49 , url = http://pubs.usgs.gov/ds/2006/155/ , isbn = 1-4113-0929-4 .Western Mountain ranges of Oregon Regions of Oregon Volcanism of Oregon