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Wind and Deserts
Wind and Deserts-Articles
Roger Weller, geology instructor
Valley of Fire, Nevada
by Robert Kelsey
Valley of Fire State Park, Nevada
Valley of Fire State Park, located in
southern Nevada, was established in 1935 to preserve dramatic sandstone
formations, including many 3000 year old petro glyphs.
Valley of Fire derives its name from red sandstone formations, formed from great
shifting sand dunes during the age of dinosaurs, 150 million years ago. Complex
uplifting and faulting of the region, followed by extensive erosion, have
created the present landscape. Other important rock formations include
limestones, shales, and conglomerates. Prehistoric users of the Valley of Fire
included the Basket Maker people and later the Anasazi Pueblo farmers from the
nearby fertile Moapa Valley. The span of approximate occupation has been dated
from 300 B.C. to 1150 A.D. Their visits probably involved hunting, food
gathering, and religious ceremonies, although scarcity of water would have
limited the length of their stay. Fine examples of rock art left by these
ancient peoples can be found at several sites within the park.
Nevada’s Valley of Fire State Park is located only six miles from Lake Mead and 55 miles northeast of Las Vegas via Interstate 15 and on exit 75. Valley of Fire is Nevada's oldest and largest state park, dedicated 1935. The valley derives its name from the red sandstone formations and the stark beauty of the Mojave Desert. Ancient trees and early man are represented throughout the park by areas of petrified wood and 3,000 year-old Indian petroglyph. Popular activities include camping, hiking, picnicking and photography. The park offers a full-scale visitor center with extensive interpretive displays. Several group use areas are also available. The park is open all year.
Nature is the Master Sculptor
Deposition of limestone, shales, and sandstones created many diverse minerals ideal for the sculptor. Earth movements arranged these materials in an interesting manner, resulting in folds, faults, and joints. But the beauty seen in the rocks of Valley of Fire is chiefly the result of that great sculpturing process of geology-erosion.
Rock, one of the hardest substances in the natural world, is gently shaped and molded into fanciful forms and shapes by water, one of the most pliable and flexible substances. Out of such a paradox is created beauty. Dark and light contrast to highlight sculpted forms. Internal structure and layering of the rock add a delicate flown to the external structure. Inner dimensions of the rock’s memory of long past events control and shape the present outline of the eroding remnants of the past.
Erosion seeks weakness in stone. The sandstone layers have soft interbeds allowing erosive forces to erode differentially. Holes form where the rock is especially vulnerable. Fanciful forms result the probing agents of the weather.
Tilted sandstone rocks are modified into
graceful shapes by the geologic process of erosion. Water is the most
active erosive agent even here in the desert. It couples with the enormity
of geologic time to achieve artistic results.
Arches are the work of nature, primarily from wind blowing sans through a weakened crack. But natures change. Once this was a solid slab wall. Someday it will be two separate pieces. Today we can enjoy the artistic form you see – a masterpiece of creation
Cementation focuses around a nucleating point such as quartz crystal or an iron grain. The binding carbonate then grows outward in spherical shell form this point. Freed by erosion at the surface, these hardened spheres weather out as “Indian Marbles”
The flow of the rock reflects the flow of time. Wrinkled, etched and scoured by
time, ancient rock walls stand exposed to the inexorable eroding forces of water
and wind. Melting snow and rainwater percolate downward through the sandstone.
The water dissolves the cementing carbonate and iron from between the grains of
sand, weakening the structure. Grain by grain the rock disintegrates. As the
water emerges along exposed rock faces, it evaporated into the dry desert air,
leaving behind residue of iron to veneer the rock with dark brown and black
patina of desert varnish.
Chemical erosion has altered original materials and created brilliant colors in
the rocks. The addition of reds by rusting iron minerals, the creation of white
sandstones leaching out of iron, and mixing of all shades of the palette of
chemical change have resulted in the colorful diversity we see today.
Chemical action has added soluble materials - lime and silica – to the
groundwater. Moving through the joints and fault surfaces of Aztec sandstone,
these chemicals occasionally find an environment for precipitation. The joints
are sometimes filled these chemicals. After precipitation the newly formed
minerals calcite or quartz, often harder than the surrounding sandstone, are
left standing as narrow ridges after the sandstone has eroded away. Where
blocks have sheared off, the vertical joints thus exposed are often veneered
with the white mineral deposits.
Other joint surfaces are coated with black substances. This “Desert Varnish”
results from chemical action, perhaps further modified by microscopic plants.
Leached from the rocks by the movement of water, iron and manganese are
deposited on the rock surface as emerges and evaporates over thousands of
years. These blackened surfaces were favored by the first inhabitants of the
Valley of Fire as ideal sites for carving rock art,
Contrary to common belief, wind has not been as active an erosion agent within the park as has water. Chemical dissolution, freezing and thawing with resultant expansion in joint surfaces, and the effect of the raindrop give water more importance than the intensity than wind as an erosive force. Anyone who witnessed the intensity of a desert of a desert thunderstorm and the power of a flash flood following it can attest to the carrying strength of water in the desert. Lack of extensive vegetation results in large amounts of erosion during floods.
Hundreds of millions of years have witnesses the creation and modification of
the materials that have made Valley of Fire one of the most geologically
interesting and scenic areas in Nevada. Preservation of this unique area for
future generations to appreciate in its natural state is a challenge to the
sensitivity and responsibility of every traveler in this geological wonderland!
The preceding Student Web Page is from my Spring Break Trip to Nevada in March 2010. All pictures taken are from my personal camera and are copyright free for non-commercial educational uses. Please credit photos to Robert M. Kelsey
Suggest Web Sites:
Nevada Division of State Parks. http://parks.nv.gov/vf.htm
Exploring the Southwest Desert USA. http://www.desertusa.com/nvval/
The American Southwest. http://www.americansouthwest.net/nevada/valley_of_fire/state_park.html
Las Vegas Review-Journal. http://www.reviewjournal.com/recreation/parks/valleyoffire.html
Fiero, G. William. Geology of the Great Basin. Reno: University of Nevada Press, 1985
Longwell, Chester R. Structe of the Northern Muddy Mountain Area, Nevada. Geological Society of
America Bulletin, Volume 60. Boulder, Colorado: 1949
Shelton, John S. Geology Illustrated. San Francisco: W.H. Freeman, 1966