Page 18 - 2007 DT 12 Issues

Basin and Range and a small area north of Elko. The see no foothills in these ranges, only
state is covered with roughly parallel alluvial fans. Large earthquakes have
ave after wave of majestic block faulted north-northeast trend- occurred on the faults over the last 1.6
mountain ranges and deep, ing ranges, on average about 10 miles million years. (Note that Nevada ranks
Wflat-bottomed valleys, one wide and up to 80 miles long. They are as the third most seismically active
after another; the territory is huge. Its iconic. The 19 century geologist C. E. state after California and Alaska.)
th
basic topographic pattern is centered Dutton characterized them as "an army The early history of the land
on Nevada and extends from eastern of caterpillars crawling northward out endowed what was to later become
California at the Sierra Nevada bound- of Mexico." the Basin and Range Province with
ary, down along the San Andreas Fault The faults (many still active) a varied geology. Much of it evolved
south through Death Valley and Pana- that are responsible for this caterpil- as a shallow continental margin. Over
mint Valley and west to central Utah’s lar topography are mostly “normal,” hundreds of millions of years, silt,
Wasatch Range. On the north end, it although some are “strike-slip.” The sand, salts, carbonates and miner-
touches the Columbia Plateau (and Walker Lane Fault Zone is a 50-mile- als accreted, layer upon layer, to be
a sliver of Idaho), then travels south wide, 500-mile-long depression of later lifted and contorted, shoved,
through Arizo- north-northwest trending strike-slip compressed and overthrusted, result-
na and New faults and ranges near the California ing in long periods of volcanism as
Mexico and border. It extends from the Garlock land masses shifted or traveled north
a few miles Fault just north of Las Vegas—which to become California. Nevada and
into the Texas intersects the San Andreas Fault—to eastern California owe their riches in
spur. It ends south-central Oregon. These gold, silver and other metals to these
just over the faults, along with the San
border in the Andreas, are accommodating
state of Sonora in Mexico. part of the motion of Pacific
The landscape is unique. Unlike and North American Plates.
the Andes or the Himalaya, which Because the upper crust
rose up through compression and of the Basin and Range is
over-thrusting, the modern Basin and thin and brittle, it breaks into
Range Pysiographic Province was long blocks as the hot, pliable
born of stretching, thinning and fault- lower crust is attenuated, al-
ing. The land has literally been pulled lowing the blocks to rise and
to pieces. tilt. Like a child’s see-saw, one
It is a relatively young landscape. end of the block rises while
Between the Sierra Nevada and the the opposite side dips down
Wasatch ranges, the crust has been into the crust, usually at an
extended by some 50 percent over the angle of 60 degrees. Offsets
last 40 million years—and it’s still of 10,000 ft or more between
stretching. It is among the thinnest the ends is not uncommon. Through igneous processes.
on the planet at 60 miles deep versus erosion the basins are back-filled, Nevada’s mineral wealth in gyp-
180 miles elsewhere. Hot springs and burying the fault and the bedrock in sum and barite is a legacy left by
geothermal pools abound. thousands of feet of debris. Strangely, the land-locked streams of the Great
Nevada is the poster child of the as these mountains shed they may rise Basin, which terminates north of Las
Basin and Range. Virtually all of the still more until the basins top out. The Vegas. With no outlet to the sea, the
state lies within it, except for the east- stressed lower crust, relieved of pres- Basin’s rivers and streams sink into the
ern Mojave Desert (Las Vegas area) sure, will boost them higher. You will ground or die out in ephemeral alkaline

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