San Juan County, Utah
San Juan County is a county in the southeastern portion of the U. S. state of Utah. As of the 2010 United States Census, the population was 14,746, its county seat is Monticello. The county was named by the Utah State Legislature for the San Juan River, itself named by Spanish explorers. San Juan County borders Arizona and New Mexico at the Four Corners; the Utah Territory authorized creation of San Juan County on February 17, 1880, with territories annexed from Iron and Piute counties. There has been no change in its boundaries since its creation. Monticello was founded in 1887, by 1895 it was large enough to be designated the seat of San Juan County. San Juan County lies at the SE corner of the state of Utah, its borders abut the borders of the states of Colorado, New Mexico, Arizona. Its terrain slopes to the west and the south, with its highest point at 12,726' ASL; the county has a total area of 7,933 square miles, of which 7,820 square miles is land and 113 square miles is water. It is the largest county by area in Utah.
The county's western and southern boundaries lie deep within gorges carved by the Colorado and San Juan Rivers. Tributary canyons, cutting through rock layers of the surrounding deserts, have carved the land up with chasms and plateaus. In the center of the county are Cedar Mesa, Comb Wash, Natural Bridges and Hovenweep National Monuments. Canyonlands National Park is within the county borders; the Eastern side of Glen Canyon National Recreation Area / Lake Powell in in San Juan County. Rising above all, the Blue Mountains and the La Sal Mountains surpass 12,000 feet elevations. Both ranges are covered with lush forests vividly contrasting with the scenery below; the elevation change within the county is from near 13,000 feet in the La Sal Mountains to 3,000 feet at Lake Powell, an elevation change of 10,000 feet. The county is cut by deep and spectacular canyons, red rock and mountain meadows and evergreen forest; the towns run on a north/south axis along U. S. Route 191 and U. S. Route 163 from La Sal in the north to Monument Valley in the south.
The only operating Uranium Processing plant in the United States operates in the town of Blanding, population 3500. San Juan County is home to numerous oil and gas fields that produce from the Desert Creek and Ismay Formations. San Juan County is bordered by more counties than any other county in the United States, at 14; as of the 2010 United States Census, there were 14,746 people and 4,505 households in San Juan County. The racial and ethnic composition of the population was 50.4% Native American, 45.8% white, 0.3% Asian, 0.2% African American and 2.3% reporting two or more races. 4.4% of the population was Hispanic or Latino of any race. As of the 2000 United States Census, there were 14,413 people, 4,089 households and 3,234 families in the county; the population density was 1.84/sqmi. There were 5,449 housing units at an average density of 0.70/km²). The racial makeup of the county was 40.77% White, 0.12% Black or African American, 55.69% Native American, 0.17% Asian, 0.03% Pacific Islander, 1.70% from other races, 1.51% from two or more races.
3.75% of the population were Hispanic or Latino of any race. In the 4,089 households, 47.00% had children under the age of 18 living with them, 60.40% were married couples living together, 14.10% had a female householder with no husband present, 20.90% were non-families. 18.70% of all households were made up of individuals and 6.70% had someone living alone, 65 years of age or older. The average household size was 3.46 and the average family size was 4.02. The county population contained 39.30% under the age of 18, 10.00% from 18 to 24, 25.20% from 25 to 44, 17.10% from 45 to 64, 8.40% who were 65 years of age or older. The median age was 26 years. For every 100 females there were 99.50 males. For every 100 females age 18 and over, there were 94.90 males. The median income for a household in the county was $28,137, the median income for a family was $31,673. Males had a median income of $31,497 versus $19,617 for females; the per capita income for the county was $10,229. About 26.90% of families and 31.40% of the population were below the poverty line, including 34.70% of those under age 18 and 35.10% of those age 65 or over.
As of 2017, San Juan County was the poorest county in the state. San Juan County has not supported a Democrat for president since Franklin D. Roosevelt in 1936; however the county is more competitive at the state level due to its high Native American population, who lean Democratic, the comparatively small Mormon population which leans Republican, as well its economic distress. Notably, San Juan voted for the Democratic candidates in the 1988 and 2000 gubernatorial elections, both of which Republicans won; the area votes less Republican than the rest of Utah in national elections. In 2004, for example, George W. Bush won 60.02% in San Juan County versus 71.54% in the state as a whole. Federally mandated commissioner districts put many Navajo voters in one district; the San Juan County Board of Commissioners has been majority white for many years. In 2016, a Federal District Court decision found voting districts violated the 1965 Voting Rights Act and the U. S. Constitution; the County was afraid to redraw district boundaries because they were put in place by a Federal Judge.
Before this the County used an at-large voting system to elect commissioners In 2018 the first majority-Navajo commission was seated. Two of the new members, Willie Grayeyes and Kenneth Maryboy, are board members of Utah Diné Bikeyah, which s
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a shallow crater lake which may be called a maar; the name comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. Maars are shallow, flat-floored craters that scientists interpret as having formed above diatremes as a result of a violent expansion of magmatic gas or steam. Maars range in size from 60 to 8,000 m from 10 to 200 m deep. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Maar lakes referred to as maars, occur when groundwater or precipitation fills the funnel-shaped and round hollow of the maar depression formed by volcanic explosions. Examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany. A dry maar results when a maar lake dries out, becomes aggraded or silted up. An example of the latter is the Eckfelder Maar.
Near Steffeln is the Eichholzmaar which has dried out during the last century and is being renaturalised into a maar. In some cases the underlying rock is so porous. After winters of heavy snow and rainfall many dry maars fill and temporarily with water; the largest known maars are found on the Seward Peninsula in northwest Alaska. These maars range in size from 4,000 to 8,000 m in diameter and a depth up to 300 m; these eruptions occurred in a period of about 100,000 years, with the youngest occurring about 17,500 years ago. Their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are explosive when the ratio of water to magma is low. Since permafrost melts it provides a steady source of water to the eruption while keeping the water to magma ratio low; this produces the explosive eruptions that created these large maars. Examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar.
Maars occur in western North America, Patagonia in South America, the Eifel region of Germany, in other geologically young volcanic regions of Earth. Elsewhere in Europe, La Vestide du Pal in the Ardèche department of France provides a spectacular example of a maar visible from the ground or air. Kilbourne Hole and Hunt's Hole, in southern New Mexico near El Paso, are maars; the Crocodile Lake in Los Baños in the Philippines was thought of as a volcanic crater is a maar. The notorious, carbon dioxide-saturated Lake Nyos in Africa is another example. An excellent example of a maar is Zuni Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about 6,500 ft across and 400 ft deep, its low rim is composed of loose pieces of basaltic lava and wall rocks of the underlying diatreme, as well as random chunks of ancient crystalline rocks blasted upward from great depths. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia and in kimberlite fields throughout Canada.
A notable field of maars is found in the Pali-Aike Volcanic Field in South America. And in the Sudanese Bayuda Volcanic Field; the Auckland volcanic field in the urban area of Auckland, New Zealand has several maars, including the accessible Lake Pupuke in the North Shore suburb of Takapuna. One of the most notable craters misidentified. In the Volcanic Eifel there are about 75 maars; these include water-filled maar lakes. Both types, lake-filled maars and dry maars, are typical of the Volcanic Eifel; the last eruptions took place at least 11,000 years ago and many maars in the Eifel are older. For this reason many are heavily eroded and their shapes and volcanic features are not as obvious as those of more recent or active maars elsewhere in the early; the maars of the Eifel are well preserved. In the Eifel and Volcanic Eifel there are numerous dry maars: Mosbrucher Weiher Booser Doppelmaar Dreiser Weiher Dürres Maar Duppacher Weiher Geeser Maar Eckfelder Maar Eigelbacher Maar Hitsche Maar Immerather Risch Gerolsteiner Maar Schalkenmehrener Maar E Schönfelder Maar Steffelner Laach or "Laach Maar" Dehner Maar Walsdorfer Maar Wollmerather Maar The following volcanic features are colloquially referred to as a "maar" or "maar lake", although they are not speaking, maars: Windsborn Crater Lake and Hinkelsmaar in theManderscheid Volcano Group near Bettenfeld, crater lakes of the Mosenberg Laacher See near Maria Laach, lake in a caldera
Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat diamond called the Star of South Africa in 1869 spawned a diamond rush and the digging of the open-pit mine called the Big Hole. The term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error. Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes, as well as igneous dykes. Kimberlite occurs as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today; the consensus on kimberlites is. Formation occurs at depths between 150 and 450 kilometres from anomalously enriched exotic mantle compositions, they are erupted and violently with considerable carbon dioxide and other volatile components, it is this depth of melting and generation that makes kimberlites prone to hosting diamond xenocrysts. Despite its relative rarity, kimberlite has attracted attention because it serves as a carrier of diamonds and garnet peridotite mantle xenoliths to the Earth's surface.
Its probable derivation from depths greater than any other igneous rock type, the extreme magma composition that it reflects in terms of low silica content and high levels of incompatible trace-element enrichment make an understanding of kimberlite petrogenesis important. In this regard, the study of kimberlite has the potential to provide information about the composition of the deep mantle and melting processes occurring at or near the interface between the cratonic continental lithosphere and the underlying convecting asthenospheric mantle. Many kimberlite structures are emplaced as carrot-shaped, vertical intrusions termed "pipes"; this classic carrot shape is formed due to a complex intrusive process of kimberlitic magma, which inherits a large proportion of CO2 in the system, which produces a deep explosive boiling stage that causes a significant amount of vertical flaring. Kimberlite classification is based on the recognition of differing rock facies; these differing facies are associated with a particular style of magmatic activity, namely crater and hypabyssal rocks.
The morphology of kimberlite pipes and their classical carrot shape is the result of explosive diatreme volcanism from deep mantle-derived sources. These volcanic explosions produce vertical columns of rock; the morphology of kimberlite pipes is varied, but includes a sheeted dyke complex of tabular, vertically dipping feeder dykes in the root of the pipe, which extends down to the mantle. Within 1.5–2 km of the surface, the pressured magma explodes upwards and expands to form a conical to cylindrical diatreme, which erupts to the surface. The surface expression is preserved but is similar to a maar volcano. Kimberlite dikes and sills can be thin, while pipes range in diameter from about 75 meters to 1.5 kilometers. Two Jurassic kimberlite dikes exist in Pennsylvania. One, the Gates-Adah Dike, outcrops on the Monongahela River on the border of Fayette and Greene Counties; the other, the Dixonville-Tanoma Dike in central Indiana County, does not outcrop at the surface and was discovered by miners.
Aged kimberlite is found in several locations in New York. Both the location and origin of kimberlitic magmas are subjects of contention, their extreme enrichment and geochemistry have led to a large amount of speculation about their origin, with models placing their source within the sub-continental lithospheric mantle or as deep as the transition zone. The mechanism of enrichment has been the topic of interest with models including partial melting, assimilation of subducted sediment or derivation from a primary magma source. Kimberlites have been classified into two distinct varieties, termed "basaltic" and "micaceous" based on petrographic observations; this was revised by C. B. Smith, who renamed these divisions "group I" and "group II" based on the isotopic affinities of these rocks using the Nd, Sr and Pb systems. Roger Mitchell proposed that these group I and II kimberlites display such distinct differences, that they may not be as related as once thought, he showed that group II kimberlites show closer affinities to lamproites than they do to group I kimberlites.
Hence, he reclassified. Group-I kimberlites are of CO2-rich ultramafic potassic igneous rocks dominated by primary forsteritic olivine and carbonate minerals, with a trace-mineral assemblage of magnesian ilmenite, chromium pyrope, almandine-pyrope, chromium diopside, enstatite and of Ti-poor chromite. Group I kimberlites exhibit a distinctive inequigranular texture caused by macrocrystic to megacrystic phenocrysts of olivine, chromian diopside, magnesian ilmenite, phlogopite, in a fine- to medium-grained groundmass; the groundmass mineralogy, which more resembles a true composition of the igneous rock, is dominated by carbonate and significant amounts of forsteritic olivine, with lesser amounts of pyrope garnet, Cr-diopside, magnesian ilmenite, spinel. Olivine lamproites were called group II kimberlite or orangeite in response to the mistaken belief that they only occurred in South Africa, their occurrence and petrology, are identical globally and should not be erroneously referred to as kimberlite.
Olivine lamproites are ultrapotassic. The distinctive characteristic of olivine lamproi
A xenolith is a rock fragment that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is exclusively used to describe inclusions in igneous rock during magma emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations in areas which are spatially limited, e.g. rhyolite-dominated lava of Niijima volcano contains two types of gabbroic xenoliths which are of different origin - they were formed in different temperature and pressure conditions. Although the term xenolith is most associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock.
Xenoliths have been found in some meteorites. To be considered a true xenolith, the included rock must be identifiably different from the rock in which it is enveloped. Xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites and lamprophyres, which have their source in the upper mantle contain fragments and crystals assumed to be a part of the originating mantle mineralogy. Xenoliths of dunite and spinel lherzolite in basaltic lava flows are one example. Kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition; the aluminium-bearing minerals of these fragments provide clues to the depth of origin. Calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase. At depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral; some kimberlites contain xenoliths of eclogite, considered to be the high-pressure metamorphic product of basaltic oceanic crust, as it descends into the mantle along subduction zones.
The large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Nixon, Peter H.. Mantle Xenoliths. J. Wiley & Sons. ISBN 0-471-91209-3
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form, but diamond never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools, they are the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is rigid, few types of impurity can contaminate it. Small numbers of defects or impurities color diamond blue, brown, purple, orange or red. Diamond has high optical dispersion. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds.
Much more they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gas by chemical vapor deposition. Imitation diamonds can be made out of materials such as cubic zirconia and silicon carbide. Natural and imitation diamonds are most distinguished using optical techniques or thermal conductivity measurements. Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common allotropes of pure carbon are graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, of all known substances diamond has the greatest number of atoms per unit volume, why it is both the hardest and the least compressible.
It has a high density, ranging from 3150 to 3530 kilograms per cubic metre in natural diamonds and 3520 kg/m³ in pure diamond. In graphite, the bonds between nearest neighbors are stronger but the bonds between planes are weak, so the planes can slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity, as well as wide bandgap and high optical dispersion. Diamond's ignition point is 720 -- 800 °C in 850 -- 1000 °C in air; the equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.
However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. Above the triple point, the melting point of diamond increases with increasing pressure. At high pressures and germanium have a BC8 body-centered cubic crystal structure, a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa; the most common crystal structure of diamond is called diamond cubic. It is formed of unit cells stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell; each side of the unit cell is 3.57 angstroms in length. A diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices with one displaced by 1/4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.
Looked at from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC... pattern. Diamonds can form an ABAB... structure, known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon. Diamonds occur most as euhedral or rounded octahedra and twinned octahedra known as macles; as diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can be elongated. Diamonds are found coated in nyf, an opaque gum-like skin; some diamonds have opaque fibers. They are referred to as opaque if the fibers
Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of diatreme. Volcanic pipes are composed of a deep, narrow cone of solidified magma, are largely composed of one of two characteristic rock types — kimberlite or lamproite; these rocks reflect the composition of the volcanoes' deep magma sources, where the Earth is rich in magnesium. Volcanic pipes are rare, they are well known as the primary source of diamonds, are mined for this purpose. Volcanic pipes form as the result of violent eruptions of deep-origin volcanoes; these volcanoes originate at least three times as deep as most other volcanoes, the resulting magma, pushed toward the surface is high in magnesium and volatile compounds such as water and carbon dioxide. As the body of magma rises toward the surface, the volatile compounds transform to gaseous phase as pressure is reduced with decreasing depth; this sudden expansion propels the magma upward at rapid speeds, resulting in a shallow supersonic eruption.
A useful analogy to this process is the uncorking of a shaken bottle of champagne. In kimberlite pipes, the eruption ejects a column of overlying material directly over the magma column, does not form a large above-ground elevation as typical volcanoes do. Over time, the tuff ring may erode back into the bowl, leveling out the depression by filling it with washed-back ejecta. Kimberlite pipes are the source of most of the world's commercial diamond production, contain other precious gemstones and semi-precious stones, such as garnets and peridot. Lamproite pipes operate to kimberlite pipes, except that the boiling water and volatile compounds contained in the magma act corrosively on the overlying rock, resulting in a broader cone of eviscerated rock; this broad cone is filled with volcanic ash and materials. The degassed magma is pushed upward, filling the cone; the result is a martini-glass shaped deposit of volcanic material which appears flat from the surface. Udachnaya pipe, a diamond mine in Yakutia, Russia Elliott County Kimberlite Lake Ellen Kimberlite American Museum of Natural History.
"The Nature of Diamonds". Retrieved March 17, 2005. Archived version Tilling. "Volcanoes". United States Geological Survey: Special Interest Publication. Retrieved March 17, 2005