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Faulted Structures -- Geology 101
This page describes faulted structures. This includes fault blocks, fault lines, splinters, overthrusts, scarps, etc.
If you wish to return to the main geology page, please click here.
Faulted structures are found where sections of the earth's crust meet one another. Ever see a dried mud puddle...completely dried and cracked into a pattern of individual pieces? Now imagine what would happen to the individual pieces of dried mud if you kicked that cracked crust around. Pieces would collide, some would overlap, some would stand on end. It would no longer resemble a cracked pattern, but rather a chaotic surface. Now, simply substitute the earth's crust for that dried mud puddle, and deep tectonic movement for the kicking motion...welcome to earth, 3rd rock from the sun.
Many of the fault phenomena described on this page can be best understood by referring to the illustration immediately below:
Seen in basin & range areas where numerous alluvial fans have formed where the fault block range is eroding. The range erodes with deep angular patterns, leaving alluvial fans as run-off. When a number of alluvial fans merge together, the resulting sloping plains are called bajadas.
Faults play into the formation of many canyons. Where a fault opens up, a canyon begins to form. The Grand Canyon, for example, is the result of a combination of uplifting, fault action, and erosion.
Outlying hunks, sort of icebergs if you will, of a range that has eroded away. Usually found "in front" of fault block type mountain ranges that have eroded away. The inselberg resembles a "mini mountain." In the diagram at the top of the page, inselbergs are visible on the pediment in the "old age" segment of a fault block mountain range.
In basin and range country, the pediment is the broad sloping area just in front of the range. It gradually slopes into the bajada (see above).
A shallow lake found in depressions in the basin and range country typical of the Western United States.
Upward thrust mountain, hill, or ridge line on the edge of a fault line. The front of tilt block or fault block mountains or ranges. The photo immediately below shows the front of the Wasatch range in Utah. It is a mature scarp. A young scarp will have a steep, solid face. A mature scarp exhibits the deep v-shaped drainage and alluvial fans seen in the photo below. An old scarp is marked by sloping pediment, inselbergs, and well worn mountains that resemble buttes more than mountains.
Faults and erosion create deep, narrow canyons; found mostly in the Colorado Plateau of Utah and Northern Arizona. Noted for stylish rock formations and flash floods.
A geologic oddity in which an older, lower layer of earth is displaced over a younger layer. One of the most notable thrust faults is found on the eastern edge of Glacier National Park, Montana. Known as the Lewis Overthrust, it is where precambrian shield thousands of feet thick has been pushed over the top of Cretaceous material that is much newer. It is evident in Flattop Mountain, where the banded layers of rock lie at a distinct angle. Chief Mountain is slightly east of the edge of the Lewis Overthrust; it is called an outlier because it is actually part of the overthrust material.
Reflects tectonic activity that has turned a layer of rock "on end," and then more recent layers have formed right beside it. Appears as a vertical stratification next to a horizontal stratification.
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