Basin and Range Province
This is a geographic zone which
occupies much of the American West, mostly lying within Nevada, Utah, Arizona, New Mexico,
Oregon, west Texas, and southern California.
Within this area, extension of the Earth's crust has caused great blocks of
crustal rock to settle downward due to gravity.
Between these blocks higher crustal pieces are seen as now-eroded mountain
ranges. Anyone driving long distances in this part of the world is familiar with the
pattern of long, wide valleys separated by narrow mountain ranges, mostly in parallel
The extension began in western North America during the Tertiary period,
around (open to debate) 25 million years ago. Arizona is in the older portion, so
our mountains are more eroded and we have relatively little earthquake activity.
Younger portions, to the north in Utah, and to the west in California, are much more
An excellent book to read if you are interested in this part of the West, is
John McPhee's Basin and Range. Many stories are woven within the context of
the geology, and it is written for the average reader, not terribly technical in its
If this window appears as a full-size,
rather empty looking web page, either you do not have scripting and "pop-ups"
enabled in your web browser, or you have found it only by way of a search function.
In the former case, you can return to the main website by using your
"Back" button, or by accessing our Home Page at www.gemland.com.
In the latter case, you will have to access our website's Home Page by going
If this window appears as a
"pop-up", simply close
this window to return to where you were.