Death Valley National Park
Geologic and Human History
By John Krist
Page 1 of 3 |
It is a harsh but beautiful realm. Golden sand dunes rise at the foot of colorful layer-cake mountains. Ancient lake beds display salty beaches created during the last ice age. Isolated stands of pinyon pines cling to the mountain summits like island dwellers in a vast sea of naked stone. Canyons carved through billion-year-old rock by seasonal flood waters slice deep into the flanks of mountain ranges with evocative names: Amargosa, Last Chance, Panamint. In the canyon walls, fossil bones and shells exposed by erosion tell the long story of life.
Death Valley National Park is the centerpiece of this region, preserving 3.3 million acres of its most spectacular and historically rich territory. It is the largest national park outside Alaska, and one of the newest, created in 1994.
Death Valley, an enclosed basin 130 miles long and from 6 to 14 miles wide, is part of the western region known as the Great Basin, which was the last part of the continental United States to be explored by Europeans and their descendants. Dry and forbidding, the Great Basin desert region is vast, stretching from the eastern foot of California's Sierra Nevada nearly 500 miles east to the Wasatch Mountains in Utah, and spanning nearly 900 miles from north to south. Its 210,000 square miles encompass almost all of Nevada, the western third of Utah, parts of California and Colorado, and small pieces of Arizona and Idaho.
Although the name conjures an image of a single great bowl, there isn't one. The Great Basin contains hundreds of north-south mountain ranges, separated by hundreds of sunken basins. The depressions are not true valleys, a name properly applied only to clefts carved or drained by streams. Instead they are blocks of the earth's crust that either have sunk between fault lines or have been left lying low as the mountains at their sides have risen along those same faults.
This combination of fault-block mountains and depressions is known as basin-and-range topography, and it is on vivid display in and around Death Valley. Starting at the foot of the Sierra and working east toward Nevada, the series of basins includes Owens, Saline, Eureka, Panamint and Death valleys, separated by such ranges as the White-Inyo, Argus, Last Chance, Panamint, Grapevine, and Funeral mountains.
Most of the Great Basin has no drainage outlet to the sea. What little precipitation does fall in this region remains there, gathering into intermittent streams and rivers that either disappear into the arid sands or drain into saline lakes.
Geologically, Death Valley is a showplace. In its barren and convoluted topography are preserved evidence of volcanoes and floods, of distant glaciers and ancient seas. It contains the lowest point in the United States—Badwater, at 282 feet below sea level—which lies literally within the shadow cast by 11,049-foot Telescope Peak.
The geological history of Death Valley goes back nearly 2 billion years, but little is known about the earliest periods. The oldest rocks exposed within the national park comprise the 1.8 billion-year-old crystalline basement formation, which is exposed in the steep front of the Black Mountains at the south end of the park and in the Panamint Mountains north of Hanaupah Canyon. These ancient rocks however, are greatly deformed, and their story cannot be deciphered.
The sequence of events becomes much clearer starting about half a billion years ago, at a time when most of what is now California was at the bottom of the sea. The western coastline of North America ran roughly north-south through the California-Arizona-Nevada junction, and for millions of years sediment washed off the edge of the continent and was deposited in shallow, warm waters there. The land-derived sediments now appear as beds of shale, sandstone and conglomerate, and are intermingled with layers of limestone and dolomite formed by thick deposits of the calcium-rich shells and skeletons of marine creatures. Good examples of these sediments, which form beds thousands of feet thick, are exposed in many of the canyons that penetrate the Panamint and the Funeral mountains.
About 140 million years ago the region began undergoing a period of volcanic activity that lasted until only a few million years ago. Molten rock welling up through the stressed and fractured continental crust formed a string of volcanoes that included cones and vents between Furnace Creek and Shoshone, and they blanketed the area with ash and cinders. The fantastic colors of the Artist's Palette formation just south of Furnace Creek inside the park were produced by weathering and chemical reactions within these volcanic ash deposits.
About 30 million years ago the landscape of Death Valley was one of lakes and wooded, rolling hills, inhabited by grazing animals such as dwarf horses and deer, as well as tapirs, rodents, rhinoceroses and dogs. Fossils of these and other creatures are found in Titus Canyon.
The topography of California as we know it today began forming about 25 million years ago, as the stress of colliding chunks of the earth's crust produced rows of fractures—faults—throughout the desert region. Along some of these faults, blocks of the earth's crust were shoved upward, while others slipped down, creating the basin-and-range topography. Death Valley, sandwiched between the Panamint and Amargosa mountain ranges, is one such basin. The geological term for this type of fault-block valley is graben, derived from the German word for"ditch."
As the faulting continued and the basins deepened and the ranges rose, the Great Basin desert became a region of interior drainage without outlet to the sea. Erosion again accelerated, and thick beds of debris were deposited in Death Valley and the other grabens of the region. Many of these basins held lakes: During the Pleistocene epoch, which began 2 million years ago and was marked by the presence of extensive glaciers in the Sierra Nevada, the Mojave River flowed above ground all the way from the San Bernardino Mountains to Death Valley. There it emptied into huge Lake Manly—since vanished, but 100 miles long and 600 feet deep at its greatest extent. Evaporation of this lake, and a much smaller one that formed during a miniature ice age about 5,000 years ago, created the salt and borate deposits found today on the valley floor.
The climate grew dry about 10,000 years ago as the last ice age ended. The Great Basin lies now in the rain shadow of the Sierra Nevada and several parallel mountains ranges, which block the flow of moisture-laden air from the Pacific and wring from it rain and snow. Only traces fall in Death Valley and the surrounding area in most years—National Park Service records show no precipitation at all in the valley in 1929 and 1953.
Geological forces at work in Death Valley today consist primarily of erosion and the motion of great blocks of the earth's crust, which continues to contort the basin-and-range province. The south end of Death Valley, for example, is still subsiding; tilt meters installed early in this century show a sinkage rate of about an inch per decade.
The sinking is partially offset by erosion and deposition of debris. Geologists have determined that beneath Badwater, a 9,000-foot-thick deposit of debris washed from the surrounding mountains rests on the bedrock floor of the Death Valley basin. If all that sand and gravel were removed the difference in elevation between the national park's highest and lowest points would be nearly 4 vertical miles. The visitor standing on the valley floor would enjoy a view of mountains rivaling the Himalayas in their soaring height.
There have been quite recent exhibitions of the more violent geological forces that have helped create the Death Valley landscape. Ubehebe Crater, produced by tremendous steam and gas explosions, formed only about 3,000 years ago. Only 2,000 years ago, a huge earthquake caused landslides, tipped the valley floor and produced fault escarpments 10-20 feet high along the foot of the Black Mountains.
These are reminders that the restless earth does not sleep, and that the period of calm modern visitors believe they live in is illusory.
Published: 28 Apr 2002 | Last Updated: 30 Mar 2010
Details mentioned in this article were accurate at the time of publication
Details mentioned in this article were accurate at the time of publication
Best Hotels in Anchorage
#1Fairfield Inn & Suites by Marriott Anchorage Midtown
#2Clarion Suites Downtown
#3Dimond Center Hotel
#4Anchorage Marriott Downtown