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36-798: At the beginning of the Rocky Mountains uplift , the final floor of the Western Interior Seaway was elevated several thousand feet (thousands of meters) above sea level. The pattern of erosion of material from the northeast into the midcontinent was largely reversed from the previous drainage patterns of the Cretaceous and earlier periods so that material eroded from the Rocky Mountains was carried eastward on to expansive, geologically weathered plains.  This material included quartz and feldspar from Precambrian granite, but also residue from

72-406: A 100,000 km middle Archean craton that was modified by late Archean volcanic magmatism and plate movements and Proterozoic extension and rifting . The Wyoming Craton mainly consists of two rock units: granitoid plutons (2.8–2.55 Ga) and gneiss and migmatite . The granitoid rocks are mainly potassic granite and were derived principally from reworked older (3.1–2.8 Ga) gneiss. During

108-415: A fairly steep angle, and a volcanic arc grows above the subducting plate. During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened , moving the focus of melting and mountain building much farther inland than is normally expected. It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with

144-580: A hardwood floor: the rug bunches up and forms wrinkles (mountains). In Canada, the subduction of the Kula plate and the terranes smashing into the continent are the feet pushing the rug, the ancestral rocks are the rug, and the Canadian Shield in the middle of the continent is the hardwood floor. Farther south, the growth of the Rocky Mountains in the United States is a geological puzzle. Mountain building

180-519: Is normally focused between 200 and 400 miles (300 and 600 km) inland from a subduction zone boundary. Geologists continue to gather evidence to explain the rise of the Rockies so much farther inland; the answer most likely lies with the unusual subduction of the Farallon plate , or possibly due to the subduction of an oceanic plateau . At a typical subduction zone, an oceanic plate typically sinks at

216-797: The Bull Lake Glaciation that began about 150,000 years ago and the Pinedale Glaciation that probably remained at full glaciation until 15,000–20,000 years ago. Ninety percent of Yellowstone National Park was covered by ice during the Pinedale Glaciation. The little ice age was a period of glacial advance that lasted a few centuries from about 1550 to 1860. For example, the Agassiz and Jackson Glaciers in Glacier National Park reached their most forward positions about 1860 during

252-747: The Cenozoic (66 million–1.8 million years ago) occurs in the San Juan Mountains and in other areas. Millennia of severe erosion in the Wyoming Basin transformed intermountain basins into a relatively flat terrain. The Tetons and other north-central ranges contain folded and faulted rocks of Paleozoic and Mesozoic age draped above cores of Proterozoic and Archean igneous and metamorphic rocks ranging in age from 1.2 billion (e.g., Tetons) to more than 3.3 billion years ( Beartooth Mountains ). Clarendonian The Clarendonian North American Stage on

288-660: The Cretaceous period when the western part of the Western Interior Seaway covered the region. Terranes started to collide with the western edge of North America in the Mississippian age (approximately 350 million years ago), causing the Antler orogeny . During the last half of the Mesozoic Era , much of today's California , British Columbia , Oregon , and Washington were added to North America . Western North America suffered

324-708: The Laramie Mountains . The Colorado orogeny was likely part of the larger Yavapai orogeny , which extended across North America and probably to other continents that were joined to North America as part of the supercontinent , Columbia . In the Paleoproterozoic, terranes also accumulated on the west side of the Wyoming Craton, forming the Selway terrane in Idaho. Mesoproterozoic (~1.4 Ga) anorthosite and syenites of

360-658: The Little Ice Age . All of the geological processes, above, have left a complex set of rocks exposed at the surface. For example, in the Rockies of Colorado, there is extensive granite and gneiss dating back to the Ancestral Rockies. In the central Canadian Rockies, the main ranges are composed of the Precambrian mudstones , while the front ranges are composed of the Paleozoic limestones and dolomites. Volcanic rock from

396-607: The Paleoproterozoic , island-arc terrane associated with the Colorado orogeny accreted to the Wyoming Craton along the Cheyenne belt , a 500-km-wide belt of Proterozoic rocks named for Cheyenne, Wyoming . As a result of the collision, older, Archean rocks of the Wyoming craton were intensely deformed and metamorphosed for at least 75 km inboard from the suture, which is marked today by

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432-600: The continental margin while others represent small isolated mid-oceanic islands. Magma generated above the subducting slab rose into the North American continental crust about 200 to 300 miles (300 to 500 km) inland. Great arc-shaped volcanic mountain ranges, known as the Sierran Arc , grew as lava and ash spewed out of dozens of individual volcanoes . Beneath the surface, great masses of molten rock were injected and hardened in place. For 270 million years,

468-763: The geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 13,600,000 to 9,000,000 years BP , a period of 3.3 million years . It is usually considered to overlap the Serravallian age of the Middle Miocene and the Tortonian age of the Late Miocene . The Clarendonian is preceded by the Barstovian and followed by

504-557: The limestone laid down in the shallow sea. The mountains eroded throughout the late Paleozoic and early Mesozoic , leaving extensive deposits of sedimentary rock . Mesozoic deposition in the Rockies occurred in a mix of marine, transitional, and continental environments as local relative sea levels changed. By the close of the Mesozoic , 10,000 to 15,000 feet (3000 to 4500 m) of sediment accumulated in 15 recognized formations . The most extensive non-marine formations were deposited in

540-687: The Colorado orogen. The breakup of the Rodinia supercontinent produced rifts between 900 million and 600 million years ago in the Neoproterozoic . These deep extensional basement faults filled with sediments, such as the Uinta rift basin and were reactivated more recently in Earth history by orogenies. The Uinta Formation and Uncompahgre Formation are both examples of remnant Precambrian rift basin sediments. The end of

576-631: The Laramie Anorthosite Complex and granite intrude into rocks of the Colorado orogen in the Laramie and adjacent Medicine Bow Mountains . Both the anorthosite and granite transect the Cheyenne belt in the Laramide Mountains, and intrude crystalline rocks of the Wyoming province. These intrusions comprise the northernmost segment of a wide belt of 1.4 Ga granitic intrusions that occur throughout

612-591: The Neoproterozoic is not known from the rock record, indicating a period of long-running terrestrial erosion which produced by the Great Unconformity , from 1.1 billion to 510 million years ago. Twelve to 24 kilometers of basement rock eroded away. During the Paleozoic , western North America lay underneath a shallow sea, which deposited many kilometers of limestone and dolomite . In the southern Rocky Mountains, near present-day Colorado and New Mexico ,

648-513: The Ogallala to group status with three members Kimball (youngest), Ash Hollow , and Valentine (oldest). Kansas geologists attempted to carry these classifications into the state; but, the state has since abandoned the three divisions. Like the remainder of High Plains states, Kansas considers the Ogallala to be a formation. However, it is convenient to informally divide the Ogallala into the three general zones with these names: Geology of

684-415: The Ogallala; Clarendonian , Hemphillian , and Blancan sufficient to attempt definitions of formations on a biostratigraphic basis. The Ogallala's rich grass seed record was also used to develop biostratigraphic successions within the unit. Unfortunately, no correlation with any consistent rock bedding can be established over the Ogallala's range. These Nebraskan biostratigraphic classifications elevated

720-660: The Precambrian and Paleozoic rocks were disturbed by mountain building approximately 300 Ma, during the Pennsylvanian . This mountain building produced the Ancestral Rocky Mountains . The uplift formed two large mountainous islands, known to geologists as Frontrangia and Uncompahgria , located roughly in the current locations of the Front Range and the San Juan Mountains . They consisted largely of Precambrian metamorphic rock , forced upward through layers of

756-611: The Rocky Mountains#Raising the Rockies The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains , a mountain system that stretches from Northern British Columbia through central New Mexico and which is part of the great mountain system known as the North American Cordillera . The rocky cores of

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792-633: The effects of plate collisions were focused very near the edge of the North American Plate boundary, far to the west of the Rocky Mountain region. It was not until 80 MA that these effects began to reach the Rockies. The current Rocky Mountains were raised in the Laramide orogeny from between 80 and 55 Ma. For the Canadian Rockies, the mountain building is analogous to a rug being pushed on

828-508: The effects of repeated collision as the Kula and Farallon Plates sank beneath the continental edge. Slivers of continental crust, carried along by subducting ocean plates, were swept into the subduction zone and scraped onto North America's western edge. These terranes represent a variety of tectonic environments. Some are ancient island arcs, similar to Japan, Indonesia and the Aleutians; others are fragments of oceanic crust obducted onto

864-439: The formation of agate and chert in the upper portion and opal in the lowest portion. Other than the lower opaline sandstone zone and the "Algal limestone", the Ogallala has no persistent lithological marker beds beyond the stated generalities of local chert beds in the upper zone and local caliche "mortar bed" lenses in the middle zone. It may be the case that consolidation of the caliche of the "Algal limestone" occurred broadly at

900-557: The high rocks, revealing the ancestral rocks beneath, and forming the current landscape of the Rockies. Multiple periods of glaciation occurred during the Pleistocene Epoch (1.8 million–12,000 years ago), finally receding in the Holocene Epoch (fewer than 11,000 years ago). The ice ages left their mark on the Rockies, forming extensive glacial landforms, such as U-shaped valleys and cirques . Recent glacial episodes included

936-414: The material deepened, particularly with the cementation of the sand and gravel with calcium carbonate and silica . The top of the Ogallala is defined by a thick cap rock of hard limestone or caliche , broadly called "algal limestone". Patterns of thin lines in the "limestone" suggested algal origin to frontier geologists (calcite and silica deposited within mats of algae under a shallow lake). However,

972-612: The material is determined to be mostly caliche that formed after deposition of the sand and gravel from the mountain rivers was sharply reduced and the climate became arid or semiarid. This extensive and resistant material established the broad flat expanses of the High Plains. Most of the material that overlies this bed is wind-blown Pleistocene loess , while the Blanco Formation overlies the Ogallala in Texas and southwestern Kansas. Much of

1008-534: The modern range; they are now visible in many places throughout the Rockies, and are prominently shown along the Dakota Hogback , an early Cretaceous sandstone formation that runs along the eastern flank of the modern Rockies. Immediately after the Laramide orogeny, the Rockies were like Tibet : a high plateau, probably 6,000 metres (20,000 ft) above sea level. In the last 60 million years, erosion stripped away

1044-491: The mountain ranges are, in most places, formed of pieces of continental crust that are over one billion years old. In the south, an older mountain range was formed 300 million years ago, then eroded away. The rocks of that older range were reformed into the Rocky Mountains. The Rocky Mountains took shape during an intense period of plate tectonic activity that resulted in much of the rugged landscape of western North America . The Laramide orogeny , about 80–55 million years ago,

1080-731: The plains in broad and overlapping alluvial fans rather than being carried into the Mississippi River.  Over this time, many volcanic ash falls occurred and have been identified to their source, including several from the Yellowstone Supervolcano  and two from the Jemez Caldera . From bottom to top, the Ogallala was deposited as overlapping alluvial fans of sand and gravel, displaying bedding resulting from river flows and flooding. Much of this material remained unconsolidated; however, significant modification occurred as

1116-558: The rivers built up the alluvial fans, subsurface water circulation varied, resulting in localized formation of caliche, and shallow lakes formed between natural levees, which deposited limestone. These consolidated lenses, distributed in within the middle portion, do not represent any particular horizon ; but do cap intermediate bluffs below valley rims. Because of their bluff-forming nature and resemblance to concrete or mortar, these lenses are described as "caprock" or "mortar beds". Various ash falls were locally deposited, supplying silica for

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1152-424: The same time but in whatever material was at the local surface after deposition of the sand and gravel ceased. And, while the "Algal limestone" is a marker bed, it does not establish correlation of the specific beds in which the caliche formed. Faced with particularly rich collections of terrestrial Neogene vertebrate fossils, Nebraska geologists recognized the distinct North American land mammal ages (NALMA) within

1188-471: The thick continental mass above it. Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range. The current southern Rockies were forced upwards through the layers of Pennsylvanian and Permian sedimentary remnants of the Ancestral Rocky Mountains. Such sedimentary remnants were often tilted at steep angles along the flanks of

1224-477: The underlying sand and gravel is unconsolidated or poorly consolidated such that it easily erodes away, leaving in western Kansas, Nebraska, and Texas a range of dramatic high bluffs that define the boundary of a "high plain". The lowest, oldest deposits filled in the shallow valleys of the weathered rocks that were exposed at that time, which ranged in age from Cretaceous in Nebraska and Kansas to Permian in Texas. As

1260-441: The uplifted shale, limestone, and sandstone accumulated from the Paleozoic and Mesozoic periods, as well as igneous rock from Cenozoic volcanism. Many rivers carried this material from the mountains to the east. What each river carried from different parts of the mountains varied, changing also as the geography of the Rocky Mountains evolved. Owing to the low amount of sloping, vast quantities of sand and gravel were dumped on

1296-403: Was the last of the three episodes and was responsible for raising the Rocky Mountains. Subsequent erosion by glaciers has produced the current form of the mountains. The rocks in the Rocky Mountains were formed before the mountains were raised by tectonic forces. The oldest rock is Precambrian Wyoming craton that forms the core of the North American continent. The Wyoming Craton originated as

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