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24-677: The Intermountain West has a basin and range and plateau topography. Some of the region's rivers reach the Pacific Ocean , such as the Columbia River and Colorado River . Other regional rivers and streams are in endorheic basins and cannot reach the sea, such as the Walker River and Owens River . These flow into brackish or seasonally dry lakes or desert sinks . Portions of this region include: The climate of

48-638: A half-graben geometry. Other common geometries include metamorphic core complexes and tilted blocks . Examples of active continental rifts are the Baikal Rift Zone and the East African Rift . Divergent plate boundaries are zones of active extension as the crust newly formed at the mid-ocean ridge system becomes involved in the opening process. Zones of thickened crust, such as those formed during continent-continent collision tend to spread laterally; this spreading occurs even when

72-419: A dip to remain active and a new set of faults may be generated. Large displacements may juxtapose syntectonic sediments against metamorphic rocks of the mid to lower crust and such structures are called detachment faults . In some cases the detachments are folded such that the metamorphic rocks are exposed within antiformal closures and these are known as metamorphic core complexes . Passive margins above

96-400: A series of normal faults which occur in groups, form in close proximity and dipping in opposite directions. As the crust extends it fractures in series of fault planes , some blocks sink down due to gravity, creating long linear valleys or basins also known as grabens , while the blocks remaining up or uplifted produce mountains or ranges, also known as horsts . Fault scarps are exposed on

120-805: A weak layer develop a specific set of extensional structures. Large listric regional faults dipping towards the ocean develop with rollover anticlines and related crestal collapse grabens . On some margins, such as the Niger Delta , large counter-regional faults are observed, dipping back towards the continent, forming large grabenal mini-basins with antithetic regional faults. Areas of extensional tectonics are typically associated with: Rifts are linear zones of localized crustal extension. They range in width from somewhat less than 100 km up to several hundred km, consisting of one or more normal faults and related fault blocks. In individual rift segments, one polarity (i.e. dip direction) normally dominates, giving

144-476: Is offset along strike such as to create a gap e.g. a left-stepping bend on a sinistral fault, a zone of extension or transtension is generated. Such bends are known as releasing bends or extensional stepovers and often form pull-apart basins or rhombochasms . Examples of active pull-apart basins include the Dead Sea , formed at a left-stepping offset of the sinistral sense Dead Sea Transform system, and

168-596: Is practiced in the region as well. Cultivated crops include corn , potatoes , sugar beets , grass hay , and alfalfa , the latter two crops are used for livestock feed. For thousands of years the Intermountain West has been the homeland for many Native American cultures, tribes, and bands. The 18th-century fur trade (northern areas), and 19th-century westward expansion of the United States brought irreversible cultural changes. The completion of

192-461: Is the most well known example of basin and range topography. Clarence Dutton compared the many narrow parallel mountain ranges that distinguish the unique topography of the Basin and Range to an "army of caterpillars crawling northward." The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch. Opinions vary regarding

216-623: The First transcontinental railroad through the region accelerated non-native settlements and development. Historically, the Intermountain West area centered in Utah is associated with Latter-day Saint (Mormon) settlements, and the region has the highest percentage of LDS members in the United States currently. That region is also known as the Mormon Corridor . The intermountain states are generally considered to be Nevada , Utah , Idaho ,

240-659: The Hellenic Subduction Zone to the south, causing extensive normal faulting and the formation of horsts and grabens on the seafloor. Many of the islands are the result of peaks reaching above sea level. One of the most studied basin and range topographies is the Basin and Range Province in the western United States, located between the Sierra Nevada and the Rocky Mountains . The extension of

264-467: The Mountain States . 40°N 115°W  /  40°N 115°W  / 40; -115 Basin and range Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling , gravitational collapse, crustal thickening, or relaxation of confining stresses. The extension results in

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288-490: The Sea of Marmara , formed at a right-stepping offset on the dextral sense North Anatolian Fault system. Back-arc basins form behind many subduction zones due to the effects of oceanic trench roll-back which leads to a zone of extension parallel to the island arc . A passive margin built out over a weaker layer, such as an overpressured mudstone or salt , tends to spread laterally under its own weight. The inboard part of

312-522: The Sierra Nevada microplate . Though the Aegean Sea Plate is more difficult to study because it is underwater, efforts have been made to conduct GPS surveys of the seafloor and surrounding area. Some studies show regions of extension within the plate, while others suggest a four-microplate model to represent the motion. The plate's deformation is thought to be a result of crustal collapse (beginning c. 14 Ma) combined with slab rollback on

336-452: The beta factor , where t 0 is the initial crustal thickness and t 1 is the final crustal thickness. It is also the equivalent of the strain parameter stretch . In areas of relatively low crustal stretching, the dominant structures are high to moderate angle normal faults, with associated half grabens and tilted fault blocks . In areas of high crustal stretching, individual extensional faults may become rotated to too low

360-488: The Hellenic Subduction Zone. Extensional tectonics Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body 's crust or lithosphere . The types of structure and the geometries formed depend on the amount of stretching involved. Stretching is generally measured using the parameter β , known as

384-585: The Intermountain Region is affected by location and elevation. The sub-regions are in rain shadows from the Cascade or Sierra Nevada ranges that block precipitation from Pacific storms. The winter weather depends on latitude . In the southern portion, winters are shorter, warmer and have less winter precipitation and snow. In the northern portion, winters are cold and moist. All areas have hot summers. North American Monsoon storms can occur in

408-527: The collisional event is still in progress. After the collision has finished the zone of thickened crust generally undergoes gravitational collapse , often with the formation of very large extensional faults. Large-scale Devonian extension, for example, followed immediately after the end of the Caledonian orogeny particularly in East Greenland and western Norway . When a strike-slip fault

432-521: The horst block and expose the footwall of the normal fault. This is a type of block faulting known as grabens and horsts . This basin and range topography is symmetrical having equal slopes on both sides of the valleys and mountain ranges. Tilted block faulting , also known as half-graben or rotational block faulting, can also occur during extension. Large gently dipping normal faults, also known as detachment faults , act as platforms in which normal faulted blocks tilt or slide along. However, instead of

456-490: The province was believed to have begun in the late Cenozoic Era, roughly 20 Ma . Between 1992 and 1998 scientists conducted GPS surveys to map the deformation of the Basin and Range province. In the study, Thatcher et al. discovered that most deformation was happening in the west, adjacent to the Sierra Nevada block, while less deformation was happening in the east. This coincides with the northwestward movement of

480-633: The region during the mid-summer, coming northeast from the Pacific Ocean and Mexican Plateau . The flora at lower elevations includes deserts and xeric shrublands and temperate grasslands and shrublands biome vegetation. Higher elevation montane habitats include temperate coniferous forests biome vegetation, including groves and forests of various species of pine , cedar , juniper , aspen , and other trees, and understory shrubs , and perennials . Intermountain West ecoregions include: Some sections are agriculturally cultivated with water diversions for irrigation systems . Cattle ranching

504-496: The thinning and deformation of the upper crust, causing it to fracture and create a series of long parallel normal faults . This results in block faulting , where the blocks of rock between the normal faults either subside , uplift , or tilt. The movement of these blocks results in the alternating valleys and mountains. As the crust thins, it also allows heat from the mantle to more easily melt rock and form magma, resulting in increased volcanic activity. With crustal extension ,

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528-443: The total extension of the region; however, the median estimate is about 100% total lateral extension. The tectonic mechanisms responsible for lithospheric extension in the Basin and Range province are controversial, and several competing hypotheses attempt to explain them. The Aegean Sea Plate consists of thinned continental crust. The northern part of the plate is currently a region of crustal extension caused by slab rollback on

552-690: The western third of Montana , Arizona north of the Mogollon Rim , Colorado from the Front Range westward, New Mexico from the central mountain chain westward, California east of the Sierra Nevada and Cascade ranges, and Far West Texas from the Pecos River westward. The intermountain states are so named from having all or portions between the Rockies, Sierras, and Cascades. The intermountain states are included among states classified as

576-408: The whole block subsiding only one side, the block may slip along the detachment fault, tilting toward the fault plane, again creating mountains (ranges) and valleys (basins), many tilted slightly in one direction at their tops due to the motion of their bottoms along the main detachment fault. This basin and range topography has one steep side and the other is more gradual. The Basin and Range Province

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