Mount Elden
Encyclopedia
Mount Elden, or Elden Mountain, is located in central Coconino County
northeast of Flagstaff
, Arizona
. It takes its name from one of the region's earliest Anglo
settlers, John Elden, who, along with his family, established a homestead on the mountain’s lower slopes and grazed sheep on the open grasslands below during the late 19th century.
The mountain’s exposed, rocky slopes are a dominant feature from almost any part of the city of Flagstaff, rising steeply nearly 730 m to an elevation of 2,834 m above sea level
. Much of the vegetation on the southern and southeastern slopes of the mountain was destroyed by a 18 km² human-caused wildfire
in June 1977.
Despite its rugged appearance, steep relief
, and nearly 40 km2 of surface area, Mount Elden is easily accessible via an extensive, well-developed road and non-motorized trail
system that is part of the Coconino National Forest
.
volcanic features within the greater San Francisco Peaks
volcanic system (part of the San Francisco volcanic field
) which include the nearby Dry Lake Hills, the Hochderffer and White Horse Hills to the northwest, and O'Leary Peak
to the northeast. Because these features developed within close proximity of the San Francisco Mountain strato-volcano there is a strong likelihood that each is a geologic subsidiary of the larger mountain.
Geologically, Mount Elden is a lava dome
composed almost entirely of dacitic
lava flows which emerged from several vents. These features emerged as intrusive
emplacements within sedimentary blocks or as viscous extrusive
flows in which the younger flows partially covered the older, lower flows. Geologic evidence suggests that the eruption of the mountain, which occurred at linear vents along regional faults, was a non-explosive event that took place during several flow sequences. Likewise, because of the high viscosity of the dacite, it is likely that the mountain formed in the short period of a few month's time. The mountain’s overlapping flows commonly take lobe-like shapes which display a variety of flow characteristics and features including concentric benches, spire
s, ramping shear fractures, longitudinal tension fractures, and conjugate shear fractures.
Positioned within the central part of Mount Elden, on the mountain’s eastern and northwestern flanks are two sedimentary
blocks. Both of these blocks display characteristics of uplift
that most likely occurred as dacitic magma
intruded into the sedimentary
strata
at a shallow depth and uplifted the layers, causing them to dip
away from the mountain. These blocks of sedimentary material are unique to the mountain, which otherwise is uniformly composed of silicic dacite.
Coconino County, Arizona
-2010:Whereas according to the 2010 U.S. Census Bureau:*61.7% White*1.2% Black*27.3% Native American*1.4% Asian*0.1% Native Hawaiian or Pacific Islander*3.1% Two or more races*5.2% Other races*13.5% Hispanic or Latino -2000:...
northeast of Flagstaff
Flagstaff, Arizona
Flagstaff is a city located in northern Arizona, in the southwestern United States. In 2010, the city's population was 65,870. The population of the Metropolitan Statistical Area was at 134,421 in 2010. It is the county seat of Coconino County...
, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
. It takes its name from one of the region's earliest Anglo
Anglo
Anglo is a prefix indicating a relation to the Angles, England or the English people, as in the terms Anglo-Saxon, Anglo-American, Anglo-Celtic, Anglo-African and Anglo-Indian. It is often used alone, somewhat loosely, to refer to people of British Isles descent in The Americas, Australia and...
settlers, John Elden, who, along with his family, established a homestead on the mountain’s lower slopes and grazed sheep on the open grasslands below during the late 19th century.
The mountain’s exposed, rocky slopes are a dominant feature from almost any part of the city of Flagstaff, rising steeply nearly 730 m to an elevation of 2,834 m above sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
. Much of the vegetation on the southern and southeastern slopes of the mountain was destroyed by a 18 km² human-caused wildfire
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
in June 1977.
Despite its rugged appearance, steep relief
Terrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
, and nearly 40 km2 of surface area, Mount Elden is easily accessible via an extensive, well-developed road and non-motorized trail
Trail
A trail is a path with a rough beaten or dirt/stone surface used for travel. Trails may be for use only by walkers and in some places are the main access route to remote settlements...
system that is part of the Coconino National Forest
Coconino National Forest
The Coconino National Forest is a 1.856-million acre United States National Forest located in northern Arizona in the vicinity of Flagstaff. Originally established in 1898 as the "San Francisco Mountains National Forest Reserve", the area was designated a U.S...
.
Geology
Mount Elden is one of five large peripheral silicicSilicic
Silicic is a term used to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually put at at least 65 percent. Granite and rhyolite are typical silicic rocks....
volcanic features within the greater San Francisco Peaks
San Francisco Peaks
The San Francisco Peaks are a volcanic mountain range located in north central Arizona, just north of Flagstaff.The highest summit in the range, Humphreys Peak, is the highest point in the state of Arizona at in elevation. The San Francisco Peaks are the remains of an eroded stratovolcano...
volcanic system (part of the San Francisco volcanic field
San Francisco volcanic field
The San Francisco volcanic field is an area of volcanoes in northern Arizona, north of Flagstaff, USA. The field covers 1,800 square miles of the southern boundary of the Colorado Plateau. The field contains 600 volcanoes ranging in age from less than 6 million years old to less than 1,000 years ,...
) which include the nearby Dry Lake Hills, the Hochderffer and White Horse Hills to the northwest, and O'Leary Peak
O'Leary Peak
O'Leary Peak is an extinct Pleistocene lava dome volcano within the San Francisco volcanic field, north of Flagstaff, Arizona. It is to the northwest of Sunset Crater. A fire tower was built at the top of the eastern peak, at an elevation of . O'Leary's western summit is at -References:-External...
to the northeast. Because these features developed within close proximity of the San Francisco Mountain strato-volcano there is a strong likelihood that each is a geologic subsidiary of the larger mountain.
Geologically, Mount Elden is a lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
composed almost entirely of dacitic
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
lava flows which emerged from several vents. These features emerged as intrusive
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
emplacements within sedimentary blocks or as viscous extrusive
Extrusive (geology)
Extrusive refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff...
flows in which the younger flows partially covered the older, lower flows. Geologic evidence suggests that the eruption of the mountain, which occurred at linear vents along regional faults, was a non-explosive event that took place during several flow sequences. Likewise, because of the high viscosity of the dacite, it is likely that the mountain formed in the short period of a few month's time. The mountain’s overlapping flows commonly take lobe-like shapes which display a variety of flow characteristics and features including concentric benches, spire
Spire
A spire is a tapering conical or pyramidal structure on the top of a building, particularly a church tower. Etymologically, the word is derived from the Old English word spir, meaning a sprout, shoot, or stalk of grass....
s, ramping shear fractures, longitudinal tension fractures, and conjugate shear fractures.
Positioned within the central part of Mount Elden, on the mountain’s eastern and northwestern flanks are two sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
blocks. Both of these blocks display characteristics of uplift
Tectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
that most likely occurred as dacitic magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
intruded into the sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
at a shallow depth and uplifted the layers, causing them to dip
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
away from the mountain. These blocks of sedimentary material are unique to the mountain, which otherwise is uniformly composed of silicic dacite.
External links
- USGS fact sheet about the San Francisco volcanic field
- Mount Elden at SummitPost.org.