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24-726: Defining the southeast border of the High Plains , the towering stone-capped bluffs of the Fort Hays Escarpment are "perhaps the most conspicuous physiographic boundary in Kansas." The Fort Hays Limestone was a generally practical building stone. However, it deteriorates when in contact with soil (note the repaired foundation on the Old Fort Hays Blockhouse). In contrast, the Fencepost limestone

48-403: A characteristic influenced by the presence of oceanic plateaus (or oceanic flood basalts). In addition to influencing slab buoyancy, some oceanic plateaus may have also become accreted to North America. It has been suggested that this deformation may go so far as to include a tear in the slab, where a piece of the subducted Farallon plate has broken off, creating multiple slab remnants. This

72-475: A weather event that occurred in Browning, Montana , from January 23–24, 1916, when the temperature fell from 44 to −56 °F (7 to −49 °C). This is the world record for the greatest temperature change in 24 hours. The region is known for the steady, and sometimes intense, winds that prevail from the west. The winds add a considerable wind chill factor in the winter. The development of wind farms in

96-641: Is quite durable in the ground, so, the Fencepost can be seen in foundation course of buildings that are otherwise faced with Fort Hays Limestone. Particularly in Hays and Ellis , where the Fort Hays and Fencepost outcrops are in close geographic proximity, the two limestones are seen in combination in buildings. This article about a specific stratigraphic formation in Kansas is a stub . You can help Misplaced Pages by expanding it . This article related to

120-543: Is supported by tomography studies and provides some more explanation of the formation of Laramide structures that are further inland from the edge. A 2013 study proposed two additional now-subducted plates that would account for some of the unexplained complexities of the accreted terranes, suggesting that the Farallon should be partitioned into Northern Farallon, Angayucham , Mezcalera and Southern Farallon segments based on recent tomographic models. Under this model,

144-627: Is usually used for a subregion instead of the whole of the Great Plains. The High Plains has a "cold semi-arid" climate — Köppen BSk —receiving between 10–20 in (250–510 mm) of precipitation annually. Due to low moisture and high elevation, the High Plains commonly experience wide ranges and extremes in temperature. The temperature range from day to night is usually 30 °F (~16.5 °C), and 24-hour temperature shifts of 100 °F (~55.5 °C) are possible, as evidenced by

168-897: The Cretaceous period is a stub . You can help Misplaced Pages by expanding it . High Plains (United States) The High Plains are a subregion of the Great Plains , mainly in the Western United States , but also partly in the Midwest states of Nebraska, Kansas, and South Dakota, generally encompassing the western part of the Great Plains before the region reaches the Rocky Mountains . The High Plains are located in eastern Montana , southeastern Wyoming , southwestern South Dakota , western Nebraska , eastern Colorado , western Kansas , eastern New Mexico ,

192-609: The Oklahoma Panhandle , and the Texas Panhandle . The southern region of the Western High Plains ecology region contains the geological formation known as Llano Estacado which can be seen from a short distance or on satellite maps. From east to west, the High Plains rise in elevation from around 1,500 to 6,000 ft (460 to 1,830 m). The term "Great Plains", for the region west of about

216-451: The convergent plate boundary than is typical of a subduction-generated orogeny . Significant deformation of the slab also occurred due to this flat subduction phenomenon, which has been imaged by seismic tomography. There is a concentration of velocity anomalies in the tomography that is thicker than the slab itself should be, indicating that folding and deformation occurred beneath the surface during subduction. In other words, more of

240-664: The 96th or 98th meridian and east of the Rocky Mountains, was not generally used before the early 20th century. Nevin Fenneman's 1916 study, Physiographic Subdivision of the United States , brought the term Great Plains into more widespread usage. Prior to 1916, the region was almost invariably called the High Plains, in contrast to the lower Prairie Plains of the Midwestern states. Today, the term "High Plains"

264-542: The Farallon slab appears as a velocity anomaly on the tomography model. Multiple studies show that the subduction of the Farallon plate was characterized by a period of " flat-slab subduction ," which is the subduction of a plate at a relatively shallow angle to the overriding crust (in this case, North America). This phenomenon is one that accounts for the far-inland orogenisis of the Rocky Mountains and other ranges in North America which are much farther from

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288-610: The High Plains have significant petroleum and natural gas deposits. The combination of oil, natural gas, and wind energy, along with plentiful underground water, has allowed some areas (such as West Texas ) to sustain a range of economic activity, including occasional industry. For example, the ASARCO refinery in Amarillo, Texas has been in operation since 1924 due to the plentiful and inexpensive natural gas and water that are needed in metal ore refining. The High Plains has one of

312-460: The High Plains is one of the newest areas of economic development. The High Plains are anomalously high in elevation. An explanation has recently been proposed to explain this high elevation. As the Farallon plate was subducted into the mantle beneath the region, water trapped in hydrous minerals in the descending slab was forced up into the lower crust above. Within the crust, this water caused

336-482: The North American continent overrode a series of subduction trenches, and several microcontinents (similar to those in the modern-day Indonesian Archipelago ) were added to it. These microcontinents must have had adjacent oceanic plates that are not represented in previous models of Farallon subduction, so this interpretation brings forth a different perspective on the history of collision. Based on this model,

360-682: The formation of the Pacific plate at the center of the triple junction during the Early Jurassic . It is named for the Farallon Islands , which are located just west of San Francisco , California . Over time, the central part of the Farallon plate was subducted under the southwestern part of the North American plate. The remains of the Farallon plate are the Explorer , Gorda , and Juan de Fuca plates, which are subducting under

384-426: The forms of cattle ranching and the growing of wheat , corn , and sunflower is the primary economic activity in the region. The region's aridity necessitates either dryland farming methods or irrigation; much water for irrigation is drawn from the underlying Ogallala Aquifer , which makes it possible to grow water-intensive crops such as corn, which the region's aridity would otherwise not support. Some areas of

408-404: The hydration of dense garnet and other phases into lower density amphibole and mica minerals. The resulting increase in crustal volume raised the elevation by about one mile. Typical plant communities of the region are shortgrass prairie , prickly pear cacti and scrub . Sagebrush steppe is also present, particularly in high and dry areas closer to the Rocky Mountains. Agriculture in

432-424: The lowest population densities of any region in the continental United States; Wyoming , for example, has the second lowest population density in the country after Alaska . In contrast to the stagnant population growth in the northern and western High Plains, cities in west Texas have shown sustained growth; Amarillo and Lubbock both have populations above 200,000 and have continued to grow. Smaller towns, on

456-661: The northern part of the North American plate ; the Cocos plate subducting under Central America ; and the Nazca plate subducting under the South American plate . The Farallon plate is also responsible for transporting old island arcs and various fragments of continental crust , which have rifted off of other distant plates. These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). During

480-571: The other hand, often struggle to sustain their population . Farallon plate The Farallon plate was an ancient oceanic tectonic plate . It formed one of the three main plates of Panthalassa , alongside the Izanagi plate and the Phoenix plate , which were connected by a triple junction . The Farallon plate began subducting under the west coast of the North American plate —then located in modern Utah —as Pangaea broke apart and after

504-457: The plate moved west, causing the following geologic events to occur: When the final archipelago , the Siletzia archipelago, lodged as a terrane, the associated trench stepped west. When this happened, the trench that had been characterized as an oceanic-oceanic subduction environment approached the North American margin and eventually became the current Cascadia subduction zone . This created

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528-420: The slab should be in the lower mantle, but the deformation has caused it to remain shallower, in the upper mantle. Multiple hypotheses have been proposed to explain this shallow subduction angle and resulting deformation. Some studies suggest that the faster movement of the North American plate caused the slab to flatten, resulting in slab rollback . Another cause of flat slab subduction may be slab buoyancy ,

552-497: The subduction of the Farallon plate, it accreted these island arcs and terranes to the North American plate . Much of western North America is composed of these accreted terranes. As an ancient tectonic plate, the Farallon plate must be studied using methods that allow researchers to see deep beneath the Earth's surface. The understanding of the Farallon plate has evolved as details from seismic tomography provide improved details of

576-461: The submerged remnants. Since the North American west coast has a convoluted structure, significant work has been required to resolve the complexity. Seismic tomography can be used to image the remainder of the subducted plate because it is still "cold," as in, it has not reached thermal equilibrium with the mantle. This is important for the use of tomography because seismic waves have different velocities in materials of different temperatures, so

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