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by The Lilies of the Valley: Amy, Alison, Jeanie, and Shellee |
The Southern San Joaquin Valley is the fourth arid region.
Climate
Characteristics of a desert environment are:
The Great Basin Desert
Located east of the cascades and the Sierra Nevada. The Great Basin climate is much cooler than the southern desert. Almost all of the precipitation occurs during the winter months, mostly the runoff of snow. The growth period is delayed until spring not like other deserts where the major period of growth is during the winter.
The most common plant of the Great Basin desert is the Great Basin Sagebrush. This plant is typical of well-drained sandy soil; it is a blue-gray shrub.
Mojave Desert
The Mojave Desert is located interior to the Transverse Ranges and South of the Great Basin. It is a large wedge-shaped basin lying between the Garlock fault on the north and the San Andreas Fault on the south. The Mojave Desert is the "High Desert" even though it includes Death Valley, with the lowest point in the United States.
It is a hot desert, precipitation mostly occurs in the winter. Vegetation here is unlike that of other deserts because of the soil is coarse and non-alkaline. The dominant life forms are the leaf-succulent yuccas, the conspicuous of which is the Joshua Tree.
Colorado Desert
This desert is called California’s "Low Desert", which is known much larger the Sonoran Desert. This southwestern desert region encircles the Gulf of California and includes northwestern Mexico, southwestern Arizona, southeastern California, and Baja California. The Colorado Desert ends at the Colorado River on the east.
It experiences more summer precipitation than the northern deserts. Precipitation remains low; most of this portion falls in August and September, usually as thunderstorms.
This desert is similar the Mojave Desert in the way that they are both sandy flats and slopes. Creosote Bush dominates over most of the area with saltbushes occurring where the soil becomes more alkaline. A distinctive feature in the Sonoran Desert is the presence of many species of trees, most of them in the pea family.
Desert Geology
The lack of water in the desert has preserved ancient rocks such as metamorphic rocks older than a billion years. Other formations include gneiss and marble, found in the Ord and Old Woman Mountains. The Pinto Gneiss is found in the Joshua Tree National Monument, and at the southern end of the Marble Mountains there are old granites and schists.
The Paleozoic Era, from about 600 million to 245 million years ago, is represented by shales, sandstone, and limestone, but they are found particularly in the Basin-Range Province.
Strategies of Desert Plants
Since water is only available for a short period of time, most plants either succulent or drought-deciduous. Succulent plants grow on the coarsest soils. They store water, which is drawn up slowly during rainstorms. Drought-deciduous plants drop their leaves during drought. After it rains, their leaves grow back rapidly. Most of these plants only drop their leaves once a year and grow new leaves up to seven times a year.
Desert Communities
Latitude influences zonation due to its effect on temperature and day length. Northern latitudes are colder and receive more precipitation as snow. The northern communities then may appear at higher elevations toward the south.
Sand Dunes
Wind is constantly carrying sand form this slope to the top of the dune, where it then slides down the other side. Major dune fields are found in each desert. In California the most spectacular dunes are the Eureka Dunes, Dumont Dunes, Kelso Dunes, and Algodones Dunes. Most sand plants have become endangered do to off road vehicles.
Desert Pavement
Desert pavement happens when wind blows away all the sand from an area. The larger pebbles and stones that remains form an armored surface preventing any more sand form being blown away. Evaporation of water from this surface leaves calcium carbonate, which can become cement that holds the stones together.
Strategies of Desert Animals
Desert animals deal with temperature extremes by avoidance.
Animals use a form of evaporative cooling. They remain in the shade
during the day in burrows. Activity periods are at dawn, dusk or
nighttime. When the climate is too severe animals go into a state of
torpor: they hibernate or aestivate.
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The Star Thistles: Naida Blevins, Miriam Koppel, Tammy Rease, Amber Shrum |
Climate
Traditionally a desert receives less than 10 inches of precipitation a year. Many California deserts receive less rain than 10 in. In Bagdad, formerly a small town in the Mojave desert, is reported to be the driest in the state receiving an average annual precipitation of 2.2 in. It holds a record from October 3, 1912 to November 8 1914, of having no precipitation. Death Valley receives an average of 1.5 in of precipitation and is the official driest place in the state.
Bishop, in the Great Basin, receives 5.6 inches of precipitation, which is mostly snow. Barstow, in the Mojave, averages 4 inches of winter rain. Imperial, in the Colorado Desert, averages 3.6 inches, including winter and summer rain. Bakersfield in the Great Central Valley averages 6 inches of winter rain.
The characteristics of a desert environment are:
A range of 50 degrees between nighttime lows and daytime highs is common. In Imperial, in the Colorado Desert, the range of temperature from the record high to the record low is 130 degrees. Air rises when it is warm and sinks when it is cool, thus causing windy conditions. The wind accelerates precipitation. In dry desert conditions 90% of the available sunlight reaches the ground, as opposed to 40% in humid areas. The desert is very hot because of these factors. The hottest day recorded in the Western hemisphere was in Death Valley, at 134.6 degrees F. The world record is the only to exceed this in Lybia at 136.4degrees F in 1922.
Low precipitation coupled with high evaporation causes the soil to be alkaline. Alkaline soil (aridasols) causes a stress for desert plants. Lack of water limits primary productivity. Photosynthesis requires water.
The Great Basin Desert
This includes two geomorphic provinces, the Modoc Plateau and the Basin-Range Province. The Modoc Plateau is a volcanic tableland that lies in the lee of the Cascades in northeastern Calif. It is the southern most tip of a large volcanic plateau known as the Columbia Plateau. It has been converted to agriculture and pasture. Gopose Lake and Eagle Lake provide abundant water. Goose Lake drains into the Pit River. The river used to flow to Sacramento River. Now the Pit River is stopped, by the Shasta Dam.
East of the Modoc Plateau is the Warner Mountains. The Warner Mountains is mostly comprised of volcanic rocks, like obsidian. Mahogany obsidian is found in the Warner Mtns.
The Basin &endash;Range Province is east of the Sierra NevadaThe northernmost valley is drained by the Walker River flowing into the Walker Lake. South of Sherwin Summit is drained by the Owens river, which drains into Owens Lake and the Mojave Desert.
The large tufa towers south of Trona were formed underwater.
The climate of the Great Basin Lake is cooler than more southerly deserts. Almost all of the precipitation falls in the form of snow in the winter. This is reflected by the dominant vegetation. The growth is delayed until spring.
The distribution of vegetation in the northern parts of Owens Valley is typical of the Great Basin Desert in California. The dominant plant may be the Single-needle Pinyon Pine or the Western Juniper. Below the pinyon pine belt is the community called the Blackbrush Scrub, so named because of the dominant Blackbush. Below this community, south of Bishop, is the Great Basin Sagebrush. This is the most common plant of the Great Basin Desert and is typical of the well-drained soil. Shadscale replaces the Sagebrush where soil is more alkaline.
Mojave Desert
The Mojave Desert is south of the Great Basin. It lies between the Garlock Fault on the north and the San Andreas Fault on the south. To the southwest it is bounded by the Transverse Ranges. To the northwest it is bounded by the Tehachapi Mountains and the southern Sierra Nevada. Included within the Mojave are Antelope Valley, Apple Valley, and Yucca Valley.
The Mojave is a hot desert. Precipitaion occurs mostly in the winter with occasion summer thunderstorms. At higher elevations thunderstorms are common. Wher snow falls and soil is coarse and nonalkaline vegetation is very distinct. Leaf succulant yuccas such as the Joshua tree are common. Above the Joshua Trees are the pinyon pines and below are the Blackbrush. Below that is the Creasote bush, which is Californias’ most abundant shrub. Where soil is too alkaline Creasote is replaced by the Shadscale. Cacti are abundant in the Mojave compared to the Great Basin and are found mostly on rocky slopes. Along washes there may be Desert Willows or Honey Mesquite, which drop their leaves in the winter.
Colorado Desert
California’s "Low Desert" is the Colorado Desert. It is the California portion of a much larger region known as the Sonoran Desert. This southwestern desert region encircles the Gulf of California and includes northwestern Mexico, southwestern Arizona, southeastern California, and Baja California.
The Colorado Desert experiences more summer precipitation than the northern deserts. Although yearly precipitation remains low, a significant portion of it falls in August and September, usually as thunderstorms.
Sandy flats and slopes in the Colorado Desert are very similar to those of the Mojave Desert. Creosote Bush dominates over most of the area with saltbushes occurring where the soil becomes more alkaline.
The California Fan Palm is a distinctive species of the Colorado
Desert, occurring in seeps and oases. From the air, groves of
California Fan Palms can be seen to outline the trace of the San
Andreas fault.
The Peninsular Ranges, along the western edge of the Colorado Desert,
show distinct banding of desert communities. Above the Cactus Scrub
community there is a zone of shrubs known as Desert Chapparal. Above
the scrub community is a zone of pinyon pines, marking the transition
to the mountain communities.
Desert Geology
The lack of water in the desert has preserved ancient landscapes. Old rock materials that have washed away in other parts of California are still present in desert mountain ranges.
Metamorphic rocks older than a billion years are found at scattered localities in the Mojave Desert. Such rock formations, including gneiss and marble, are found in the Ord and Old Woman mountains.
The Mesozoic Era, from about 245 million to 65 million years ago, was a time of subduction, when the continent was moving westward over the ocean crust. The magma formed during this interval is represented by plutonic rocks throughout the west.
During the Cenozoic Era, from about 65 million years ago to the present, the desert area accumulated freshwater sediments and volcanic rocks indicating that the terrain was above sea level. One exception to this is found on the north side of the El Paso Mountains near Red Rock Canyon. This area, uplifted along the El Paso fault, a portion of the Garlock fault system, includes a series of stream and lake deposits dates at about 58 million years of age.
About 25 million years ago (Miocene) the picture of California as we see it today began to emerge. About this time the west coast changed to become a faulted, rifted borderland.
Right-lateral faulting along the San Andreas fault pulled Baja California away from what is now mainland Mexico. This rifting opened up the Gulf of California, of which the Salton Trough of the Colorado Desert is merely the northern end.
Northward (right-lateral) movement along the San Andreas fault may be the driving force causing left-lateral movement along the Garlock fault.
Intermittent flooding and volcanism also added to the Miocene record of the California deserts. Some of the oldest beds of tuff, ash, and other interbedded volcanics are in Red Rock Canyon, they are estimated to be 58 million years old. Mixed with other volcanics through out the southwestern deserts are the shales, siltstones, sandstones and conglomerates. In Death Valley the Artist’s Drive is an area where you can see the playa deposits and conglomerates. Other areas of displayed lake sediment deposits are in Zabriskie Point and Artist’s Pallette.
Badlands are areas where the lake bed deposits have been eroded, they support very little plant life. A plant that grows in the badlands and nowhere else is the wildflower Gilmania luteola (a member of the buckwheat family).
A series of marine deposits in the Colorado Desert are known as the Imperial Formation, these deposited have been uplifted along the Elsinore fault. These deposits contain 200 marine invertebrate species fossils.
Palm Spring Formation is a badlands formation in Anza-Borrego Desert State Park. It contains fossils of the vertebrates of the Pliocene period, such as, llamas, mastodons, sloths, lions, sabertooth cats, just to name a few. During this period deserts experienced heavy rainfall, the desert basins were large lakes. There is also evidence of volcanic activity in the layer of volcanic ash.
The Salton Sea which is 235 feet below sea level is fed by irrigation runoff; the last freshwater invasion ended 500 years ago.
Most of the desert volcanic activity occurred in the Miocene age or later. The Calico Mountains are an example of a mixture a of volcanic and sediments of the Miocene age. In the eastern Mojave the layering of ash and rhyolite are quite spectacular between the Providence Mountains and the New York Mountains. Basalts compose the younger volcanics, these formed in the Pleistocene and continued since then. There are approximately 45 volcanic formation near Little Lake in Owens Valley. Rainbow Canyon is also an exceptional scene to take in east of Owens Valley. Pinanmint Valley is painted with red and yellow volcanics.
Volcanic Cones, including Amboy and Pisgah craters in the Mojave were most likely formed by eruptions 2000 years ago. The Ubehebe Crater in the northern end of Death Valley was formed by a steam and volcanic ash that fell back on itself forming layers of bedded sediments. In the Colorado Desert the volcanics are mildly active, the mud pits have since been covered by the Salton Sea, yet some remain visible near Niland.
The earth’s heat has been converted into electricity. Geothermal facilities to be built in the deserts are in planning. There are already several facilities operating south of the Salton Sea, near the southern end of the Coso Range, near Mammoth Lakes and at Agua Prieta. Agua Prieta is one of the oldest working geothermal power plants.
Vegetation specific to volcanic landscapes includes Atriplex hymenelytra (Desert Holly).
Mining in California’s deserts has been an important economic activity. The mining silver, lead, and zinc in the Inyo, Panamint and Argus Mountains has been highly profitable. In the Mojave the most important silver mines were in the Rand Mountains, gold in the Panamint, Rand and Cargo Muchacho Mountains. A small amount of the metal tungsten has been mined in the gravels of the Rand Mountains. Desert gold mining is not over the cyanide help leaching technique still occurs.
Iron has also been found in the desert, the largest mine was in the Eagle Mountains, the Kaiser Steel Company operated this mine until the 1900s.
Most of today’s mining is for sand and gravel, though evaporites are also valuable. The Trona mine produces potash, used in fertilizers.
Boron used in jet fuel can be found in Searles Lake in the form of the mineral borate. Death Valley also contains these minerals (colemanite and ulexite). The largest mine in near the town of Boron.
Gypsum, used in Plaster of Paris is an evaporite composed of calcium sulfate. Talc is also mined in the desert mountains. Rare-earth minerals are also found in the desert, used in glassmaking, petroleum and metallurgy, the important mineral is bastnaesite mined in area where the Clark Mountains and Interstate 15 cross.
Joshua Tree Woodland
Joshua Tree habitat is well-drained loose gravel and sand, on the upper part of gentle slopes. The Joshua Tree Woodland is similar to Blackbrush Scrub. Joshua Trees (Yucca brevifolia), the symbol of the Mojave Desert, are pollinated by yucca moths and produce white flowers when temperature and precipitation are favorable. The germination of the tree's seeds occurs with the winter rain, but rarely survive the predation of rodents. Survival is increased for those trees located under nurse plants.
Joshua Trees are host to many insects. The Yucca Weevil larvae kill stem tips, thereby creating branching. This action makes the Yucca Tree the largest flowering plant in the Mojave Desert.
Approximately 25 different species of birds have been identified in the Joshua Tree habitat. The most obvious are the woodpeckers, which thrive in the environment due to the soft wood of the Yuccas and the abundance of termites. Lizards also benefit from the supply of termites. Snakes such as the Night Snakes live under the fallen boughs and feed on the lizards and a variety of insects.
Antelope Valley, in the western portion of the Mojave Desert, was the fastest growing area in the state in the 1980s. Ordinances were created to protect the Joshua Trees and other sensitive species.
PAGES 514-515 Survival in a Food-poor Ecosystem
Overgrazing in the already deficient ecosystem causes erosion and arroyos, the increase of weeds and unpalatable species. The food production is so poor that it takes 10 acres to support 1 steer or 5 sheep (without any other herbivorous animals). California’s desert produces a mere 3% of beef, yet it is harsh on the desert ecosystem and millions of dollars are spent for predator control there. Desert grazing can destroy the microbiotic crust of the soil, which functions as an absorbent for water and prevents erosion from water and wind. The problem of overgrazing is increased by feral "domesticated" animals (horses and burros). Those animals have been hunted in the past until Congress passed laws in 1971. It is believed that there are approximately 2,100 feral horses in California. The issue of how to control the feral horse population continues to be a matter of debate among ranchers, BLM, and animal rights activists. Likewise, Burros pose a threat to native plants and animals competing for food and water. The Burros who take over the few water holes that exist have particularly threatened the Bighorn Sheep. BLM has created "adopt-a-burro", a program to relocate the Burros.
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by Jane Wright, The Chickadees |
Climate
A desert is an area that receives less than 10 inches of precipitation per year. Some of the deserts in California receive even less. Our deserts also have wide variation in when they obtain their precipitation.
Desert Average Precipitation Type of Precipitation Great Basin 5.6 inches majority in winter snow
Mojave 4.0 inches winter rain
Colorado 3.6 inches winter and summer rain
Characteristics of a desert are:
- Low, unevenly distributed precipitation, less than 10 inches a year
- Temperature extremes (can range 50 degrees in a day)
- Windy &endash; rapid temperature changes caused by air rising when warmed and sinking when cooled causes desert air to move rapidly creating wind
- High light intensity &endash; air is dry which is clear letting 90% of the sunlight to reach the ground as compared to 40% which is normal
- Nutrient-poor, alkaline soil &endash; low precipitation and high evaporation causes soil to be alkaline, course soil and lack of organic material causes nutrients to be deficient
- Low rates of primary production &endash; lack of water is the main reason for low production
Great Basin Desert
The Modoc Plateau and the Basin-Range Province make up the Great Basin Desert area. Using water from several lakes to irrigate the land, the Modoc Plateau is being used as agriculture and pasture land. Located further north the Great Basin is cooler than the other California deserts therefore; its growing season is in the spring vice the winter. Like the Great Basin the drainage is internal (does not flow to the sea) flowing into a salt lake. The most common plant in this desert is the Great Basin Sagebrush. Other plants include the Blackbrush, Shadscale, and some Pinyon Pine. These plants all grow in their own niches.
Mojave Desert
The Mojave Desert is called the "High Desert" and is located south of the Great Basin. It also has the low spot in the United Sates &endash; Death Valley at 282 feet below sea level. The Mojave is a very hot desert with its precipitation falling mostly in the winter in the form of rain and snow. The dominant vegetation is the Joshua Tree. Other plants are pinyon pines and Blackbrush, Creosote Bush, Shadscale, and cactus. Located in some washes you can find Desert Willows, or Honey Mesquite.
Colorado Desert
The Colorado Desert is part of the Sonoran Desert and is called the "Low Desert." A lot of the Colorado Desert lies within the Salton Trough with the Salton Sea at its lowest point. The precipitation in the desert falls mainly in the winter, but it does experience some summer rain as well. The dominant plant is the Creosote Bush. Other plants include Cactus Scrub, Desert Agave, and Ocotillo. Located in washes you can find Blue Palo Verde, Ironwood, mesquites, and Smoke Trees. In seeps and oases the California Fan Palm grows. Desert Chaparral and pinyon pine grow at the western edge of the desert.
Desert Geology
Due to the climate in the deserts you can find ancient landscapes that have survived the test of time. The Mojave Desert has metamorphic rocks older that a billion years old. Shales, sandstones, and limestones are left over from the Paleozoic Era when the deserts were cover with seawater. There are granites left over from the era of subduction &endash; 65 million years ago. Since 65 million years ago the deserts areas built up freshwater sediments and fossils of land mammals indicating that the areas were now above sea level.
From 25 millions year ago to today the major faulting transpired. The west coast began moving northward along the San Andreas Fault this caused the deserts to spread. The Garlock fault affected the Basin-Range Province. The faulting caused the mountains to uplift and the valleys to sink. It also caused rivers to be blocked or redirected leaving freshwater lakes without runoff and to eventually dry up. Volcanism was another important aspect in the creation of the deserts changing the landscape, leaving lava deposits, disturbing the soils, and leaving sediments. Volcanism deposited many useable minerals and ores making mining a significant economic pursuit in our deserts. Mineral and ores found are gold, silver, lead, zinc, tungsten, iron, salts, potash, potassium, borates (colemanite, ulexite, and kernite), gypsum, talc, and rare earths.
Joshua Tree Woodland
Joshua Trees are usually grown in areas that have well-drained loose gravel and sanded soils. They also prefer gentle sloping terrain. These trees form the overstory for some very important understory plants. Without some of these plants, particularly the "nurse plants" the Joshua Trees might all be destroyed by rodents. Many animals and insects are associated with the Joshua Trees including Yucca moths, Yucca weevil, termites, and 25 species of birds (most conspicuous - Northern Flickers and Ladder-backed Woodpeckers). Reptiles also call the areas near Joshua Trees home such as Desert Night Lizards and the Night Snakes.
Overgrazing of the Deserts
Overgrazing of herd animals has dramatically affected California Deserts. Only 20% of Bureau of Land Management’s land in not overgrazed by cattle and sheep. Herd animals grazing changes and destroys the natural vegetation and increases the distribution of weeds. They also compact the soil, which increases run off, and erosion. The bottom line is that the deserts cannot support the magnitude of the herd animals that are allowed to graze. Due to the low productivity in the desert, it is estimated that at least 10 acres are required to support a single cow or five sheep. Feral horses, burros, and donkeys are a growing problem for the desert ecology. Overgrazing has also destroyed or does not provided sustenance for the natural desert animals such as the Desert Bighorn Sheep.
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The Mama's and Papa's |
1. Great Basin Desert
2. Mojave Desert
3.Colorado Desert
Climate
A region that receives less 10 inches traditionally classified desert
Calif. deserts dry, but very considerably in temp
6 Characteristics of desert environment
1. Low, unevenly distributed precipitation, less than 10 inches per year
2. Temp. extremes
3. Windy, increased evaporation rates
4. High light intensity
5. Nutrient-poor, alkaline soil
6. Low rates of primary production
Dryness influences many factors-Dry air changes temp rapidly because little
water vapor to moderate change.
Dry air is very clear, about 90% of available sunlight reaches the ground,
compared to 40% in a humid climate.
Desert soil is also a product of dry climate low rain fall and high
evaporation rate causes soil to be alkaline- posing osmotic stress for
desert plants which already are water stressed
THE GREAT BASIN DESERT
Great Basin Desert includes 2 geomorphic provinces
1.Modoc Plateau - is a volcanic tableland that lies in the of Cascades in
N.E. Calif.
2. Modoc Plateau has been converted extensively to Ag and pasture with lake
in area such
As Goose Lake and Eagle Lake providing abundant water supply.
Not all Great Basin is desert. Numerous ranges- ecologic islands -that rise
above the Great Basin Desert.
During the Pleistocene, the Ice age, there were periods of heavy rainfall in
the deserts. The Owens River flowed beyond Owens Lake to China Lake
Climate of Great Basin Desert is cooler than more southerly deserts-almost
all precipitation occurs in winter.
MOJAVE DESERT
Mojave Desert is south of the Great Basin
Mojave Desert is the "High Desert" of the weather report, even though it
includes Death Valley the lowest point in the U.S.
Mojave is a hot desert -precipitation occurs mostly in the winter-some
occasional summer thunderstorms. Snow in the higher elevations is common
COLORADO DESERT
Colorado Desert is the "Low Desert" is the Calif portion of a much larger
region known as the Sonoran Desert.
Colorado Desert experiences more summer precipitation that the northern
deserts -yearly rainfall low -a significant portion falls in August and September.
Sandy flats and slopes in the Colorado Desert very similar to those of the
Mojave Desert. Creosote Brush dominates over most of the area with saltbushes occurring where soil becomes alkaline.
Distinctive feature of Sonoran Desert is the presence of many species of trees, most from the pea family
DESERT GEOLOGY
Lack of water in the desert has preserved ancient landscapes. Old rock
materials that have washed away in other parts of California are still
present in the desert mountains ranges.
Metamorphic rocks older than a billion years are founded scattered
localities in the Mojave Desert.
One billion to 600 million years ago, during the Proterozoic, a period of
erosion stripped away many thousands of feet rock throughout most of the
southwest.
Paleozoic Era from about 600 million to 245 million years ago, is
represented by shales, sandstones and limestones that exposed throughout the
deserts, but particularly in the Basin Range Province where the uplift of
mountains along dip-slip faults has exposed them, these sedimentary rocks
represent the interval of time when the western border of North America was
a continental shelf covered by seawater.
Mesozoic Era from about 245 million to 65 million years ago was a time of
subduction, when the continent was moving westward over the ocean crust.
The magma formed during this interval is represented by plutonic rocks
throughout the west.
During the Cenozoic Era from about 65 million years ago to the present the
desert area accumulated freshwater sediments and volcanic rocks indicating
that the terrain was about sea level.
About 25 million years ago (Miocene) the picture if Calif. as we see it
today
began to emerge. About this time the west coast changed to become a
faulted, rifted borderland
Miocene record in Cali. deserts is represented not only by uplift and
subsidence, but also by intermittent flooding and volcanism.
Eroded lakebed deposits are called badlands because they will support very
little plant life. Water sinks slowly and the soil clings to the water so
that it is difficult for plants to grow there.
Volcanism in the desert areas is mostly of Miocene age or younger. In the
Great Basin this includes the Modoc Plateau. Miocene volcanics are scattered
throughout the Mojave and Colorado deserts
Younger volcanics are mostly dark-colored basalts -these rocks are abundant
in Owens Valley.
Several conspicuous cone in the Mojave extending in a line from Barstow
eastward including Amboy and Pisgah craters
Colorado Desert recent volcanics are represented by a line of pumice and
obsidian dome near the southern end of the Salton Sea.
Geysers are a form of recent volcanism and provide geothermal energy.
Volcanic landscapes often have specific vegetation (Desert Holly)
Mining important economic activity to Cal Deserts, large amounts of silver,
lead and zinc have been mined
Gold was obtained in mine in Panamint mountains and gold is still being
mined with the process of cyanide heap leaching
JOSHUA TREE WOODLAND
Joshua Tree Woodland is very similar to Blackbrush Scrub, occurring at
similar elevations with similar climate where snow is a common form of
precipitation. Many species in common in the communities and some
authorities lump them together
Joshua Tree (Yucca brevifolia) from overstory in this community, although
they appear to dominate in terms of actual biomass they are probably less
important than the understory. Joshua Trees are the symbol of the Mojave Desert.
Joshua Tree germinate with abundant winter precipitation but are usually
gnawed off by rodents They need the protection of nurse plants
Number of animals known associates of Joshua Trees Yucca moths, Yucca weevil
25 birds have been reported to Joshua Tree for nesting
PAGES 514-515
Overgrazing of livestock is evident by the photos taken before the
introduction of livestock
Problem is the low productivity of life to sustain livestock 10 acres needed
to support 1 animal unit of livestock but to support wildlife 70 acres is
considered a minimum
Effect of overgrazing have been well documented but only recently shown the
effect on the cold deserts disturbances of the soil can destroy microbiotic
crust that includes stabilizing filaments of blue-green algae and nitrogen
fixing lichens which absorbs and prevents erosion
Until 1971 Gov agencies hunted feral animals to keep them under control
sometimes meat was sold for pet food and exported to Europe
Number of feral horse increasing and could become a problem/ Main problem
is ranchers view the horses as direct competition to cattle for grazing
Burros numbers continue to increase, have no natural enemies and have over
grazed and compacted vast stretches of Mojave terrain to the detriment to
native plants and animals/one of most seriously affected animal is the
Desert Bighorn Sheep because burros take control of the limited water
holes/sheep populations have decreased rapidly/the adopt a burro program
experienced difficulty keeping up with the birth rate of the burros
Go to Other Chapter Summaries!
Marilyn Cannon, November 25, 2002