Basin and Range Province
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The Basin and Range Province is a particular type of topography that covers much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys. Death Valley is a good example of a modified basin and range valley.
The basins are down-fallen blocks of crust and the ranges are relatively uplifted blocks, many of which tilt slightly eastward at their tops. The normal arrangement in the basin and range system is that each valley (i.e., basin) is bounded on each side by one or more normal faults that are oriented along or sub-parallel to the range front.
This arrangement is very similar to the horsts and grabens seen in divergent plate boundaries such as the Mid-Atlantic Ridge or in failed rifting areas such as the Western Rift of the Great Rift Valley in East Africa. However the extent of the rifting in the Basin and Range is not concentrated into a single valley but is spread out over a very large area creating much smaller grabens lying roughly parallel to each other in a north-south direction (which leads to a rain shadow effect resulting in exceedingly dry conditions in this province).
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[edit] Geography
The province extends east from the Sierra Nevada all the way to the Colorado Plateau and extends south over northern parts of the Baja California Peninsula. This covers parts of the U.S. states of Arizona, California, Idaho, New Mexico, Texas, Oregon, and Utah and almost all of Nevada. Basin and Range topography also dominates large parts of the Mexican states of Sonora, Chihuahua, and Baja California. The arid Great Basin is part of this province as well as most of the Sonoran Desert and the Chihuahuan Deserts.
[edit] Geology
The topography of the Basin and Range is a result of crustal extension within this part of the North American Plate. The cause of this extension is as yet not fully understood, although several hypotheses have been offered. The crust here has been stretched up to 100% of its original width.[1] In fact, the crust underneath the Basin and Range, especially under the Great Basin, is some of the thinnest in the world. Along the roughly north-south-trending faults mountains were uplifted and valleys down-dropped, producing the distinctive alternating pattern of linear mountain ranges and valleys of the Basin and Range province.
[edit] Mineral resources
The Basin and Range province supplies nearly all the copper and most of the gold, silver, and barite mined in the United States. A small amount of petroleum is produced within the province, in Nevada.
[edit] See also
- Geologic timeline of Western North America
- Copper mining in Arizona
- Gold mining in Nevada
- Silver mining in Arizona
- Silver mining in Nevada
[edit] References
- ^ http://geomaps.wr.usgs.gov/parks/province/basinrange.html Geologic Provinces of the United States: Basin and Range Province
- Steven M. Stanley, Earth System History (W.H. Freeman and Company; 1999) pages 537, 540-543, 545 ISBN 0-7167-2882-6
- Plummer, McGeary, Carlson, Physical Geology, Eight Edition (McGraw-Hill: Boston, 1999) pages 321, 513, 514 ISBN 0-697-37404-1
[edit] Further reading
- Basin and Range by John McPhee, Noonday Press, 1990. ISBN 0-374-51690-1
- Geology of the American Southwest : A Journey Through Two Billion Years of Plate Tectonic History by W. Scott Baldridge, Cambridge University Press, 2004. ISBN 0-521-01666-5
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