West Valley College Death Valley Field Trip, Spring Break 2001!
Gowler Gulch + Badwater Basin
Family + Badwater Basin
Golden Canyon 1
Golden Canyon 2
Golden Canyon 3
Golden Canyon 4
Golden Canyon 5
Densely Welded Tuff
Little Hebe Crater
|Welcome to WVC's Death Valley field trip.
Where is the Death Valley (CA map 1)? Death Valley is in the Basin and Range province of California. It is the third basin in this province east of the Sierra Nevada (CA map 2). Recent Basin and Range extension (100%) has exposed Paleozoic and Precambrian rocks that tell a story of a much different tectonic setting for California during this time. These old rocks tell us that California was a Trailing Continental Margin, much like today's East Coast of North America. There were miles of white quartz sandy beaches, beautiful coral reefs, and warm tropical waters. This tectonic setting was very un-California-like!
The recent extensional tectonic setting of the Basin and Range has given it the geomorphology of mountain ranges and basins that extend from east of the Sierra Nevada to the base of the Wasatch Range in Utah. This region is also known as the Great Basin of North America and extends north to south from Oregon-Idaho down to southern Sonora and Chihuahua, Mexico. The basins or valleys are called grabens (German for ditch) and the ranges are called horsts. These ranges are bound by range-front faults, which are normal faults where an enormous amount of displacement has occurred. For example, the Sierra Nevada Fault is a range-front fault where there has been about 14,000 feet of displacement between the Owens Valley and the High Sierra in the vicinity of Mt. Whitney. Death Valley is known as a half-graben. Here, only the Black Mountains (Armagosa Range) are bound by a range-front fault. The Panamint Range to the west of the valley forms part of a tilted block, sliding on a detachment fault. These detachment faults can yield wildly deformed and metamorphosed rock called mylonite. Next time you are at Badwater (lowest point in the U.S.A. at 282 feet below sea level), take a look at the Black Mountains just to the east. These are known as Turtlebacks, intensely micro-brecciated metamorphic rock of Precambrian age (about 1.7 billion years old). The origin of the metamorphic fabric may be due to mylonitization along the detachment fault underlying Death Valley. The rocks may be some of the oldest exposed in Death Valley, but the fabric of the Black Mountains is probably due to Late Cenozoic extension (2 to 3 million years old)!
Lake deposits, playas, and shoreline erosion features called strandlines tell us that Death Valley was once filled by a very large lake. This lake was called Lake Manly. Shoreline Butte, in the southern end of the valley, contains a series of benches cut by wave action. The highest identifiable wave-cut bench or shoreline is over 285 feet above sea level. The lowest point in Death Valley is 282 feet below sea level. This means that Lake Manly was over 500 feet deep and about 100 miles long! So where did all the water come from and where did it go? We look to the Sierra Nevada for this evidence. During the Pleistocene Epoch, North America experienced a "Great Ice Age". The height of the glacial period occurred about 18,000 years ago. By 10,000 years ago (the end of the Pleistocene), the alpine glaciers in the Sierra Nevada had mostly melted. Much of this water flowed to California's Great Valley; however, a large percentage flowed to the closed basins of California's Basin and Range province. In fact, Death Valley was the lowest point, and the Mojave River and Amargosa River fed Lake Manly for thousands of years. The water has now evaporated due to a warmer climate change. The best evidence for this evaporated water is in the playa. We see salt pans, which are composed of evaporite minerals like halite, gypsum, and borate minerals.
There are many more chapters in the history of Death Valley and the Basin and Range province. We still have not discussed the recent volcanism and the spectacular Ubehebe Crater, nor have we discussed the spectacular action of wind. Sand Dunes, Race Track Playa, Ventifact Ridge, Mushroom Rock just to name a few. Death Valley is tectonically active. Both normal faults and strike slip faults may be found in the valley. This leads to some unusual geologic structures.
Join us on our
trip this Spring Semester, 2002. When will you have the opportunity to visit a
spectacular region like Death Valley? You will gain knowledge, but more importantly
you will gain the experience of traveling and seeing for yourself!
|Feel free to e-mail me:
E-Mail: Robert Lopez
Copyright © 2001 - Robert Lopez
All Rights Reserved
Last updated: November 27, 2001