Tumtum Mountain is a small, highly-symmetrical

volcanic cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and ...

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. Located in northern Clark County at the easternmost end of Chelatchie Prairie, it rises to an elevation of , about above the flat prairie. This

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 ...

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 ...

lava dome is part of the

Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern Calif ...

, and with an age of only about 70,000 years, Tumtum Mountain is the youngest and westernmost volcano in the Cascades of Washington state.

Geography and access

Tumtum Mountain is located among the foothills of the Cascade Range, about east of

Washington State Route 503 State Route 503 (SR 503) is a state highway serving Clark and Cowlitz counties in the U.S. state of Washington. The highway travels north from a short concurrency with SR 500 in Orchards through Battle Ground, the eastern ter ...

via NE Healy Rd, whose junction is just north of the

Mount St. Helens National Volcanic Monument Mount St. Helens National Volcanic Monument is a U.S. National Monument that includes the area around Mount St. Helens in Washington. It was established on August 27, 1982, by U.S. President Ronald Reagan, following the 1980 eruption. The 110,0 ...

headquarters in Chelatchie (officially

Amboy, Washington Amboy () is a census-designated place (CDP) in Clark County, Washington, United States. The population was 1,838 at the 2020 census, up from 1,608 at the 2010 census. It is located 33 miles northeast of Vancouver which is part of the Portland-V ...

). Healy Rd becomes Forest Road 54 as it enters

Gifford Pinchot National Forest Gifford Pinchot National Forest is a National Forest located in southern Washington, managed by the United States Forest Service. With an area of 1.32 million acres (5300 km2), it extends 116 km along the western slopes of Cascade Ran ...

and traverses along the northern base of Tumtum Mountain, and a gated

logging road A gravel road is a type of unpaved road surfaced with gravel that has been brought to the site from a quarry or stream bed. They are common in less-developed nations, and also in the rural areas of developed nations such as Canada and the Unit ...

ascending the north flank provides access to the mountain. The active stratovolcano of

Mount St. Helens Mount St. Helens (known as Lawetlat'la to the indigenous Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United St ...

is located only to the north-northeast, easily visible from the summit of Tumtum Mountain on clear days. The historic Yale Bridge, a one-lane metal suspension bridge built in 1932 over the steep canyon of the Lewis River at the eastern end of Lake Merwin, is located about to the northwest on SR 503. Yale Dam, a high hydroelectric dam built in 1953, is located about 2 miles (3 km) to the north of the mountain.

Geology

Tumtum Mountain was apparently formed by

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

rising to the surface along the northeasterly-striking Chelatchie Fault, which passes along the southern edge of Chelatchie Prairie and underneath the mountain. The surrounding rocks in the area are mostly much older

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 ...

ic lava flows, pyroclastics, and sediments of 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'', " ...

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 ...

age (i.e. 5–40 million years old), heavily eroded and weathered. Much later, in the

(within the last 10,000 to 2 million years), a large

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

filled the Lewis River valley, with an ice thickness reaching an elevation of in the vicinity of Tumtum Mountain, higher than the present summit. Glacial drift deposited by this glacier covers almost all of the region, but none is found on Tumtum Mountain itself, and the mountain shows no evidence of

glacial erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...

, so it must be younger than this last regional glaciation. Geologists estimate its age at around 70,000 years. The rock of Tumtum Mountain is a very fine-grained light buff to gray

, with

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

content of 68%, fairly typical and similar to that found in the lava domes of

. The

of Tumtum Mountain consists of talus and fragments of this dacite surrounding the lava dome itself. In addition, a small dacite lava flow is found on the north side at the base of the mountain, overlying the regional glacial drift.

History

The land on Tumtum Mountain has been owned by a succession of logging companies over the past several decades, including

Crown Zellerbach Crown Zellerbach was an American pulp and paper conglomerate based in San Francisco, California, purchased in a hostile takeover in 1985. Most of its pulp and paper assets were sold to James River Corporation, now part of Georgia-Pacific. I ...

Cavenham Forest Industries Cavenham is a village and civil parish in Suffolk, England, northwest of Bury St Edmunds. It is in the local government district of West Suffolk, and the electoral ward of Icini. At the 2001 UK census, Cavenham Parish had a population of 127. ...

, and then private logging company owner Billie McKee Sr. since 1988. At some point the entire mountain was logged by one of these owners. An estate sale in 2011 placed a 360-acre (150 hectare) parcel containing the majority of the mountain on the market for $1.4 million, later reduced to $699,900.

References

External links

{{Commons category-inline Volcanoes of Washington (state) Pleistocene lava domes