Specimen Ridge, el. is an approximately ridge along the south rim of the Lamar Valley in

Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowst ...

. The ridge separates the Lamar Valley from Mirror Plateau. The ridge is oriented northwest to southeast from the Tower Junction area to

Amethyst Mountain Amethyst Mountain, el. is the highest peak and central part of a northwest – southeast trending ridge that lies between the Lamar River to the northeast and Deep Creek to the southwest within Park County, Wyoming. From northwest to southeast, ...

. The ridge is known for its abundance of amethyst,

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

and petrified wood. It was referred to as ''Specimen Mountain'' by local miners and was probably named by prospectors well before 1870. The south side of the ridge is traversed by the Specimen Ridge Trail between Tower Junction and

Soda Butte Creek Soda Butte Creek is an approximately long major tributary of the Lamar River in Yellowstone National Park. It is named for a now-extinct geyser (Soda Butte) near its mouth. Soda Butte and the creek were named by A. Bart Henderson, a Cooke City m ...

. The trail passes through the Petrified Forest and over the summit of Amethyst Mountain el. .Schneider, Bill (2003) ''Hiking Yellowstone National Park.'' Falcon Press, Guilford, Connecticut. 101 pp. (pp. 199–202)

Geology

Specimen Ridge consists of a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

known as the Lamar River Formation. Within the Specimen Mountain area, it consists predominantly of an undetermined thickness of conglomerate that is interbedded with lesser proportions of

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

aceous

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

and siltstone.

Volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

is absent. The conglomerates consist of a mixture of

mudflow A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...

deposits (

lahars A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley. Lahars are extremel ...

) that are complexly interlayered with braided and meandering stream deposits. The lahar (mudflow) deposits consist of normally massive and structureless, matrix-supported conglomerates that contain subangular, poorly sorted gravel that range in size from to in diameter. The majority of the sediments consist of well-bedded, clast-supported fluvial conglomerates that consist of grain-supported, subrounded, and moderately well-sorted gravel that typically ranges in size from to . The vast majority of

petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ' ...

occurs within the conglomerates. The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

leaves, needles, pollen, and cones are largely found within tuffaceous sandstones and siltstones that were deposited either along the banks of either braided or meandering rivers, within their abandoned channels, or in shallow lakes of very limited extent. At Specimen Ridge, these sediments consist of volcanic material eroded from and accumulated downslope of an adjacent Eocene stratovolcano, known the 'Washburn Volcano', in an intermountaine basin. The Lamar River Formation is part of the Washburn Group.Fritz, WJ (1980a) ''Depositional Environment of the Eocene Lamar River Formation in Yellowstone National Park.'' Doctoral Dissertation, The University of Montana, Missoula, Montana.Fritz, WJ (1980b) ''Stratigraphic framework of the Lamar River formation in Yellowstone National Park.'' Northwest Geology. vol. 9, pp. 1-18.,Fritz, WJ (1981) ''Reinterpretation of the depositional environment of the Yellowstone fossil forests: Reply.'' Geology. 9(2):53-54.Fritz, WJ (1982) ''Geology of the Lamar River Formation, northeast Yellowstone National Park.'' In SG Reid and DJ Foote, eds., pp. 73-101, Geology of Yellowstone Park Area. Wyoming Geological Association Guidebook, 33rd Annual Field Conference, 1982, Wyoming Geological Association, Casper, Wyoming.Feeley, TC, MA Cosca, MA and CR Lindsay (2002) ''Petrogenesis and implications of calc-alkaline cryptic hybrid magmas from Washburn Volcano, Absaroka Volcanic Province, USA.'' Journal of Petrology. 43(4):663-703. The Lamar River Formation is part of the Absaroka Volcanic Supergroup. It is a thick accumulation of volcanic rocks that were either erupted from or eroded from the slopes of two belts of Eocene stratovolcanoes. These rocks accumulated within an intermountain basin between these belts. Before they were destroyed by erosion, these volcanoes are estimated to have had peaks that rose about to above adjacent intermountain valleys. Depending on location, the Lamar River Formation

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

overlies either older

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 ...

s, conglomerates, tuffs, volcanic breccias of the Sepulcher Formation; Mississippian

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

s; or Precambrian

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

. Based on radiometric dates and plant fossils from it, the Lamar River Formation is considered to be of Middle Eocene age.Smedes, HW, and HJ Prostka, 1972
''Stratigraphic framework of the Absaroka Volcanic Supergroup in the Yellowstone National Park region.''
Professional Paper no. 729-C, U. S. Geological Survey, Reston, Virginia. 33 pp.

Yellowstone Petrified Forest

Within the Specimen Ridge, exposures of the Lamar River Formation is well known for the

s of upright standing, petrified tree trunks and multiple beds containing buried

petrified forests Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ' ...

and

concentrations. The concentrations of silicified wood, upright standing, petrified tree trunks, and associated buried petrified forests of Specimen Ridge and adjacent Amethyst Mountain are collectively known as ''Yellowstone Petrified Forest''. They have been known to science and studied for over 130 years.Holmes, WH (1879) ''Fossil forests of the volcanic Tertiary formation of Yellowstone National Park. Geological and Geographical Survey of the Territories.'' Bulletin of the Survey vol. 5, no. 1, pp. 125-132. United States Geological and Geographical Survey, Department of the Interior, Washington DCKnowlton, FH (1914
''The Fossil Forests of Yellowstone National Park.''
National Park Service, Department of the Interior, Office of the Secretary, Washington DC. 31 pp. Last accessed September 26, 2013.Dorf, E (1960) ''Tertiary fossil forests of Yellowstone National Park, Wyoming.'' in DE Campau, HW Anisgard, and RL Egbet, pp. 253-260, Guidebook, 11th Annual Field Conference, Billings Geological Society, Casper, Wyoming.Dorf, E (1964) ''The 'petrified forests' of Yellowstone Park.'' Scientific American. 210(4):106-114.Dorf, E (1980
''Petrified Forests of Yellowstone.''
National Park Service, U.S. Department of Interior, Washington, D.C., 31 pp. Within Specimen Ridge, the Yellowstone Petrified Forest consists of a mixture of fossilized, in place (''

in situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...

'') buried forests and beds of transported logs and stumps. The rare beds that contain buried forests were buried in place (''

'') by volcanic lahars and braided streams. The concentrations of fossilized upright stumps, flat-lying logs, and logs lying at various angles were transported from the higher slopes of adjacent volcanoes and buried by either volcanic lahars or braided and meandering streams.Karowe, AL. and TH Jefferson (1987) ''Burial of trees by eruptions of Mount St. Helens, Washington; implications for the interpretation of fossil forests.'' Geological Magazine. 124(3):191-204. Notably, the

1980 eruption of Mount St. Helens On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive er ...

, and other Quaternary and

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

eruptions Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...

of other Cascade Range volcanoes have created virtually identical beds containing either the buried upright standing trunks of forests, transported logs and upright stumps, or a combination of both. These beds consist of a mixture of lahars and stream deposits.Fritz, WJ (1983) ''Comment on 'Erect floating stumps in Spirit Lake, Washington' '' Geology 11(12):733-734Fritz, WJ, (1980c) ''Reinterpretation of the depositional environment of the Yellowstone "fossil forests".'' Geology. 8:(7):309-313.Fritz, WJ, and S Harrison (1985) ''Transported trees from the 1982 Mount St. Helens sediment flows--Their use as paleocurrent indicators.'' Sedimentary Geology 42(1-2):49-64.Cameron, KA, and PT Pringle (1991
''Prehistoric buried forests of Mount Hood.''
Oregon geology. 53(2):34-43. Prehistoric logs and upright trunks that are buried in Late Pleistocene lahar and stream deposits of Mount St. Helens were found to be the initial stages of being naturally petrified by

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 ...

. In regard to these fossil forests and other fossils, collecting of fossils in Yellowstone National Park is illegal. In addition, visitors should stay on marked and maintained trails.

References

External links

* Anonymous (nd
''Petrified Forest''
National Park Service, Washington DC. * Viney, M (2008

{{Petrified forests Ridges of Wyoming Landforms of Yellowstone National Park Landforms of Park County, Wyoming Petrified forests Tourist attractions in Park County, Wyoming Paleontology in Wyoming

Geology

Yellowstone Petrified Forest

See also

References

External links