Fortress Mountain is a peak in the

Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...

located about west of

Lake Chelan Lake Chelan ( ) is a narrow, long lake in Chelan County, north-central Washington state, U.S. Before 1927, it was the largest natural lake in the state by any measure. Upon the completion of Lake Chelan Dam in 1927, the elevation of the lake was ...

in Chelan/ Snohomish Counties,

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 ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. It straddles the border between the

Mount Baker-Snoqualmie National Forest Mount is often used as part of the name of specific mountains, e.g. Mount Everest. Mount or Mounts may also refer to: Places * Mount, Cornwall, a village in Warleggan parish, England * Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, C ...

and the

Wenatchee National Forest Wenatchee National Forest is a U.S. National Forest located in Washington. With an area of 1,735,394 acres (2,711.55 sq mi, or 7,022.89 km²), it extends about 137 miles along the eastern slopes of the Cascade Range of Washington, USA from ...

, and is also part of the

Glacier Peak Wilderness Glacier Peak Wilderness is a , , wilderness area located within portions of Chelan, Snohomish, and Skagit counties in the North Cascades of Washington. The area lies within parts of Wenatchee National Forest and Mount Baker National Forest a ...

. Fortress Mountain is the highest point on Chiwawa Ridge, and other notable peaks on this ridge include Napeequa Peak, Buck Mountain, Brahma Peak, Bandit Peak, Mount Berge, Helmet Butte, and

Chiwawa Mountain Chiwawa Mountain is an mountain summit located in the Glacier Peak Wilderness of the North Cascades in Washington state. The mountain is situated on the crest of the Cascade Range, on the shared border of Snohomish County and Chelan County, ...

Geology

The Glacier Peak Wilderness of the North Cascades features some of the most rugged topography in the

with craggy peaks, ridges, and deep

glacial valley U-shaped valleys, also called trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape in cross-section, with steep, straight s ...

s. Geological events occurring many years ago created the diverse topography and drastic elevation changes over the Cascade Range leading to the various climate differences. The history of the formation of the Cascade Mountains dates back millions of years ago to the late

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

Epoch. With the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...

overriding the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

, episodes of volcanic igneous activity persisted. In addition, small fragments of the

oceanic Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places * Oceanic, British Columbia, a settlement on Smith Island, ...

and

continental lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years o ...

called

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

s created the

North Cascades The North Cascades are a section of the Cascade Range of western North America. They span the border between the Canadian province of British Columbia and the U.S. state of Washington and are officially named in the U.S. and Canada as the Cascad ...

about 50 million years ago. During the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), 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 fina ...

period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured the landscape leaving deposits of rock debris. The "U"-shaped cross section of the river valleys are a result of recent glaciation.

Uplift Uplift may refer to: Science * Geologic uplift, a geological process ** Tectonic uplift, a geological process * Stellar uplift, the theoretical prospect of moving a stellar mass * Uplift mountains * Llano Uplift * Nemaha Uplift Business * Uplif ...

and faulting in combination with glaciation have been the dominant processes which have created the tall peaks and deep valleys of the North Cascades area.

Climate

Most

weather front A weather front is a boundary separating air masses for which several characteristics differ, such as air density, wind, temperature, and humidity. Disturbed and unstable weather due to these differences often arises along the boundary. For in ...

s originate in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, and travel east toward the

Cascade Mountains The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...

. As fronts approach, they are forced upward by the peaks of the Cascade Range, causing them to drop their moisture in the form of rain or snowfall onto the Cascades (

Orographic lift Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and cr ...

). As a result, the Cascades experience high precipitation, especially during the winter months in the form of snowfall. During winter months, weather is usually cloudy, but, due to high pressure systems over the Pacific Ocean that intensify during summer months, there is often little or no cloud cover during the summer.Beckey, Fred W. Cascade Alpine Guide, Climbing and High Routes. Seattle, WA: Mountaineers Books, 2008. The months July through September offer the most favorable weather for viewing or climbing this peak.

References

External links

* Weather forecast
Fortress Mountain
{{SnohomishCountyWA-geo-stub Mountains of Chelan County, Washington Mountains of Snohomish County, Washington North American 2000 m summits

Geology

Climate

See also

References

External links