Where the rocky mountains are relatively located
The Columbia Icefield is situated on the continental divide in the Canadian Rockies at elevations of 10, to 13, feet 3, to 4, metres above sea level. It includes the large Athabasca Glacier , which is nearly five miles long and about a mile wide. Glaciers in this ice field, while continuing to move, are thinning and retreating. The Canadian Rockies are about equally divided between drainage to the east Atlantic and Arctic oceans and west Pacific Ocean.
While the massive deposition of carbonates was occurring in the Canadian and Northern Rockies from the late Precambrian to the early Mesozoic, a considerably smaller quantity of clastic sediments was accumulating in the Middle Rockies. Mountain building there resulted from compressional folding and high-angle faulting, except for the low-angle thrust-faulting in southwestern Wyoming and southeastern Idaho.
The granitic core of the anticlinal mountains often has been upfaulted, and many ranges are flanked by Paleozoic sedimentary rocks e. This same mountain-building process is occurring today in the Andes Mountains of South America. Most mountain building in the Middle Rockies occurred during the Laramide Orogeny, but the mountains of the spectacular Teton Range attained their height less than 10 million years ago by moving more than 20, vertical feet relative to the floor of Jackson Hole along an east-dipping fault. The Bighorn, Wind River, and Uinta ranges all form sharp ridge lines that rise above surrounding basins.
These glaciers, however, are retreating fairly rapidly.
Geology of the Rocky Mountains
Geologic events in the Middle Rockies strongly influenced the direction of stream courses. A special feature of the past 10 million years was the creation of rivers that flowed from basin floors into canyons across adjacent mountains and onto the adjacent plains. This phenomenon resulted from superposition of the streams. The stream courses were initially established in the late Miocene Epoch about During the subsequent regional excavation of the basin fills—which began about five million years ago—the streams maintained their courses across the mountains and cut deep, transverse canyons.
The Yellowstone-Absaroka region of northwestern Wyoming is a distinctive subdivision of the Middle Rockies. A large magma chamber beneath the area has filled several times and caused the surface to bulge, only to then empty in a series of volcanic eruptions of basaltic and rhyolitic lava and ash. Three such cycles have occurred in the past two million years, the most recent of which occurred about , years ago. The magma chamber is currently filling again, and the land surface in Yellowstone is rising or tilting a slight amount each year.
The eastern and western ranges are separated by a series of high basins: from north to south they are North Park, the Arkansas River valley, and the San Luis Valley. Only about 5, feet of sediment accumulated during middle Mesozoic times about to million years ago in the region now occupied by the Southern Rockies. Mountain building in these ranges resulted from compressional folding and high-angle faulting during the Laramide Orogeny, as the Mesozoic sedimentary rocks were arched upward over a massive batholith of crystalline rock.
Some 10, vertical feet of the sedimentary rocks were then eroded; otherwise the Front Range would be approximately twice its present height. The Southern Rockies experienced less of the low-angle thrust-faulting that characterizes the Canadian and Northern Rockies and the western portions of the Middle Rockies.
Rocky Mountains - Wikipedia
The ranges of the Southern Rockies are higher than those of the Middle or Northern Rockies, with many peaks exceeding elevations of 14, feet. Colorado has 53 peaks over this elevation, the highest being Mount Elbert in the Sawatch Range , which at 14, feet 4, metres is the highest point in the Rockies.
These ranges were heavily eroded by several episodes of glaciation—the most recent ended about 7, years ago, and no active glaciers remain—resulting in spectacular alpine scenery. River valleys have been deepened in the past two million years, first from the direct action of glacier ice and subsequently by glacial meltwaters.
Looping, knife-edged moraines occur in most valleys, marking the downslope extent of past glaciations. The physiographic province called the Colorado Plateau in southeastern Utah , southwestern Colorado, northern Arizona, and northwestern New Mexico is another high-elevation region of the western United States , although it lacks the history of folding, faulting, and volcanic activity of adjacent regions.
The uplifts in the Colorado Plateau are not as great as those elsewhere in the Rockies, and therefore less erosion has occurred; Precambrian rocks have been exposed only in the deepest canyons, such as the Grand Canyon. The plateau is actually a series of plateaus at different elevations arranged in a stairstep sequence through faulting. The horizontal sedimentary rocks have been dissected by the Green and Colorado rivers and their tributaries into a network of deep canyons. Such sedimentary remnants were often tilted at steep angles along the flanks of 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.
Colorado Location of
In the last 60 million years, erosion stripped away the high rocks, revealing the ancestral rocks beneath, and forming the current landscape of the Rockies. Periods of glaciation occurred from the Pleistocene Epoch 1. The ice ages left their mark on the Rockies, forming extensive glacial landforms, such as U-shaped valleys and cirques. Recent glacial episodes included the Bull Lake Glaciation that began about , years ago and the Pinedale Glaciation that probably remained at full glaciation until 15,—20, years ago. 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. 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.
From Wikipedia, the free encyclopedia. International Geology Review. Bibcode : IGRv Handbook of the Canadian Rockies. Corax Press. Johnson; Robert G.
Raynolds Roadside Geology of Colorado. Geology of National Parks Fifth ed. Retrieved Canadian Rockies Geology Road Tours. Bibcode : Natur.
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