Imperial Sand Dunes
Tremendous earth upheavals that elevated the area above the ocean some 200 million years ago and the constant action of erosional forces over the eons have all had a part in sculpturing this vast region. For millions of years, the climate of California's desert area was tropical.
But as the earth's crust shifted along the San Andreas fault, the coastal mountains were pushed up, cutting off the moisture laden air coming from the ocean. At the same time, the interior plains of Southern California began to drop, forming a basin known as the Salton Sink. Gradually, the region dried, forcing many plants and animals to adapt or perish.
The Colorado River flowed through country so flat that the meandering course of the river varied over a wide area, being periodically diverted in one direction or another by silt deposits remaining after floods. Sometimes, the river flowed into the Gulf of California as it does today, while at other times it turned westward into the Salton Sink. Each time the Salton Sink received the river flow, a large freshwater lake formed. Scientists refer to this ancient body of water as Lake Cahuilla (ka-WEE-ah). The last Lake Cahuilla covered much of the Imperial, Coachella and Mexicali Valleys as late as 1450.
The most popular theory holds that the Imperial Sand Dunes were formed from windblown beach sands of Lake Cahuilla. The prevailing westerly and northwesterly winds blew the sands eastward from the old lakeshore to their present location This process continues to this day.
Prevailing winds cause the dunes to migrate toward the southeast at the rate of approximately one foot per year. The primary force shaping the dunes is wind, and by understanding the relationship of wind to sand, you can learn to "read" the dunes. Dunes are generally oriented at right angles to the wind. Since the wind here generally blows west to east, the dune crests generally follow a north-south orientation.
The side of the dune west of the crest is the "windward" side, because that's the side the wind blows against. The side away from the wind (east side) is the "leeward" side. The windward slope of the dune follows a gradual curve resulting from the sand grains being pushed up the slope by the wind. As the sand grains blow over the crest, they go over the brink into air so still that they simply drop straight down. Most sand grains land high on the leeward slope, which tends to over steepen the slope so that from time to time thin tongues of sand slide down it. For this reason, the upper steep portion of the leeward slope is called the "s1ipface."
The bigger the dune, the bigger the slipface. Two of the largest and best known are Competition Hill and the Brawley Slide (Oldsmobile Hill). The slipface will be steepest just after a big windstorm. Many dune vehicle accidents result from failing to anticipate the slipface. The vehicle races up the windward side, and before the driver knows what's happening the rig jumps off the slipface and is airborne. On large dunes, a vehicle may drop 50 feet or more before landing in the sand below, sometimes with fatal results. Study the dunes carefully to learn to expect a slipface on the other side!
Vegetation & Wildlife
Although sand dunes are often viewed as being lifeless, a number of specialized plants and animals have adapted to this unique environment. Constant movement of the sand and a lack of water near the surface have produced a relatively sparse vegetative cover on the dunes themselves, but a number of species are common. Creosote bush extends into the dunes along the east and west edges of the dune system where many recreationists camp.
Other smaller species extend into the central dunes and include sandpaper plant, desertbuckwheat, desert witchgrass, silver-leaved dune sunflower, Pierson's locoweed, three- forked ephedra, plicate coldenia and others. These dunes plants have adapted by developing root systems which support them in the unstable sand and penetrate deep to reach water. In the spring, some areas are dotted with colorful annuals such as dune primrose and sand verbena.
A number of dune plants are considered rare or threatened because they occur only in this very specialized type of environment. Examples are the silver-leaved dune sunflower, Pierson's milkvetch, and Giant Spanish needle. Sandfood, a parasitic plant which obtains its food by tapping the roots of nearby desert shrubs, is an unusual dune resident which appears on the surface each spring. The condition of these and other plant and wildlife species is being closely monitored using funds from a variety of sources, including the State OHV Fund, to insure that the dunes are managed to provide both recreational opportunities and viable habitat for sensitive species.
Large open pockets nearly free of dune formation are found east of the crest of the dune system. These relatively stable low areas catch the runoff from summer and autumn rains in the mountains to the east and support such desert woodland species as ironwood, palo verde, honey mesquite, screwbean mesquite, desert willow and other trees and shrubs. Most large wildlife species seek the protection of the heavier vegetation along the dune periphery, though such mammals as coyote and mule deer are occasionally seen crossing the dune system. Rabbits, ground squirrels and a variety of birds, lizards and insects are seen throughout the dunes.
Gecko Campground is named for one the most common sand dune inhabitants, the Banded Gecko. This small lizard has smooth skin which makes it appear like a creature from a swamp, but its body has a number of features that clearly suit it for life on the desert. The gecko's unique notched eyelids interlock to keep sand out of its eyes. Its long tongue can be used to lick its eyes clean if necessary. If you don't see a gecko, it's probably because these lizards hibernate during much of the winter and are active only at night during other times of the year. On a quiet spring evening you might hear a gecko, though. They are one of the few lizard species to have a voice, which is presumably used to call a mate.
The sand dunes have long been an obstacle to travelers moving east and west in the vicinity of the Imperial Valley. Juan Bautista de Anza and other early explorers were forced to detour around the dune system. Though a few pioneers did manage to cross with horse and mule pack trains, this natural barrier continued to hinder California's southern commerce until the first road across the dunes was built in 1911.
The Southern Pacific Railroad was constructed along the eastern edge of the dunes late in the nineteenth century. Company towns of Glamis, Amos, and Ogilby grew around railroad sidings. Today, only Glamis survives, primarily because it is located on State Highway 78 at an important staging area for sand dune recreationists.
From 1951 through 1964, portions of the dunes were used as a U.S. Naval Impact Range. While the area has been searched for unexploded ordnance, shifting sands continue to expose dangerous shells, rockets and practice bombs. Beware of suspicious objects! DO NOT TOUCH UNEXPLODED ORDNANCE. If possible, mark the area and report the location to BLM.
The sand dunes contain little evidence of early man's permanent habitation. The dunes were crossed by travelers moving between ancient Lake Cahuilla and the Colorado River. Temporary campsites, often containing roasting pits, broken pottery and arrowheads are sometimes found along the east and west edges of the dunes.
Please leave all cultural resources as you find them and inform the nearest Bureau of Land Management (BLM) office of their location so that they can be studied in place by archaeologists. Removal of or damage to artifacts is prohibited and punishable by fines or imprisonment.
-- Source: California BLM
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