Joshua+Tree

** Welcome to Joshua Tree! By Christie Ledingham and Nikki Salzman**


Introduction Joshua Tree National Park is in southeastern California, situated 140 miles away from Los Angeles in Twentynine Palms, California. The latitude of the park is 34 o 4' 10”, and the longitude is 116 o 23' 20” 8. Joshua Tree contains parts of the Mojave Desert as well as the Sonoran (or Colorado) Desert. The main difference between these deserts is their elevations, with the Mojave higher than the Sonoran-- this creates slightly different environments 5. The national park has 954,242.688 arces of federal land, and 63,505.35 acres of privately owned land, meaning that there is a whopping gross area of 1,017,748.03 acres 6. Yet, it is not on the top ten biggest national park list of the United States. Joshua tree is known for it’s beautiful geologic formations, as well as spectacular cacti and unique yucca and Joshua trees. In spite of the harsh climate of the desert, there is diverse plant and animal life for great observation. It was designated as a national treasure in 1994, when the United States congress passed the California Desert Protection Act, made for conserving California’s natural desert areas. In Joshua Tree National Park, there are many highlighted features to explore. For example, there are innumerable nature hikes and trails, camping sites, look outs, and rock climbing boulders. Also, there are opportunities to rent out mountain bikes and explore the dirt roads of the park. If one is interested in observing, there are many birds to observe as well as wildflowers, yuccas, cacti, and the Joshua trees. The prime time to observe the annual wildflowers in lower elevations is February, March, and April. If exploring higher elevations having altitudes of 3,000 – 5,000 feet such as in the Mojave desert, it would be better to go from March to May. For Cacti in lower elevations, visting in March, April and May is the best. Higher up, aim for April to June. For both higher and lower elevations, both Yucca and Joshua trees bloom throughout March and April 8. For hiking trails, the first great trail is the Boy Scout Trail, which takes 1 -2 days to complete and is moderate in difficulty. In total, the trail is 25.8 kilometers, or 16.0 miles roundtrip. The Boy Scout trail is a scenic trail through the edge of the Wonderland of Rocks. The Wonderland of Rocks is huge, pancake or loaf-like stacks of rocks, columns or spires of rock, and even some huge domes. Each structure is unique, for they were all formed by different events over millions of years. A famous rock climbing area is called Hidden Valley, as it has many handholds and footholds 8.

Geologic Setting Joshua Tree National Park’s signature type of rock is granite. Granite is light in color and igneous. It is light in color because it’s two main components are feldspar which is pink and quartz, which is a washy white. This igneous rock is formed in deep intrusions, and not only in this area. Granite covers a large amount of California’s mountain ranges from Mexico all the way to the Sierras in Nevada. Granite cools very slowly, as it was magma. Because it cools so slowly, its minerals have the chance to grow very organized into large and tightly locked grains.



One part of why Joshua Tree National Park is so interesting is because of its surplus of strange boulder formations. Sometimes, the boulders seem strategically balanced atop one another, for each is perfectly smooth and rounded. The process of formation for these boulders is quite logical. Thousands of years ago, the land was covered with soil, and the climate was not like the desert of today. The bedrock was a granitic rock called monzogranite 3. As the groundwater ran through the rock, it started to chemically weather it. Since the bedrock was this type of granite, the feldspar turned to clay while the quartz pieces became loose due to the now present clay. The most weathered part of the rock was the edges because it had the most surface space for erosion 7. As the climate changed into the present day desert climate, the sand and clay were easily eroded away by water and wind, resulting in the breakup of the granite to reveal its new, rounded, free-floating boulders. It broke in such rectangluar pieces because the monzogranite has characteristic vertical and horizontal joints that form from the groundwater. Some of these boulders are left balanced atop another, explaining the strange formations 9.

The Hidden Valley climbing area is so popular as mentioned before because of its ringed rocky granite walls, handholds, footholds, as well as its strong fabric of vertical and horizontal jointing. Joints are careful cracks in rock due to stresses. There are three different kinds of jointing: the first is when the joint is parallel to the surface of the rock exposure, so that it looks layers; the second is when the joint runs up vertically, and the third is when it runs diagnonally. Joints are similar to faults except that there is no movement along them. Jointing sometimes removes pressure off of rock under it, exposing the underlying rock and letting the top rock erode. The stresses that form faults are compressional stress, meaning that the rock has pressure pushing in; tensional stress, meaning that the rock has pressure pulling it apart; and strike- slip stress, meaning that the rocks slide by each other. Fault stresses are also common in jointing stress. Something else spectacular in Joshua Tree National Park is the Keys View scenic lookout over the San Andreas fault. This lookout is in the southern part of the park and is at one of the highest parts of the park. The San Andreas fault runs vertically through California, at more than 800 miles long. It is a transform boundary of strike-slip faults occurring along it. This means that it is neither creating lithosphere like in divergent boundaries, or destroying lithosphere as in convergent subduction boundaries. In millions of years, this means that there is the possibility of Western California breaking off of it’s native spot, and moving up towards Alaska. Geologists think that over its 15-20 million year existence, it has displaced 150 miles. This is calculated from an annual displacement rate of 2 inches per year. Faults do not just affect the rocks of the park. When the bedrock shifts along a fault, the groundwater flow is changed because sometimes non-permeable rocks end up in places where permeable rocks once were. When this happens, the groundwater has nowhere else to go but up, so it comes to the surace and forms small oases 7. These oases are critical water sources for desert plants and animals in Joshua Tree.



Erosional Features of the Desert

Surprisingly, most of the desert erosion comes from the effects of running water and groundwater. Occasional late summer tropical storms come up from the south and bring quick, heavy rains that cause flash flooding 2. Alluvial fans are often the result of flash flooding because the runoff water quickly dragged sediment off the mountains into a fan-like shape at their bases 7. These flash floods also cause small lakes right after they occur, but for the rest of the dry season, these lakebeds are dry and flat. They are called playa. The second most prominent erosional feature is wind. As wind sweeps over an area, it picks up the fine particles on the ground in the process of deflation 7. This occurrs until there is only a layer of large, packed particles on the ground—this is desert pavement. The wind also erodes the rocks in the park through the process of abrasion, when wind-blown sand cuts and polishes the surface of rocks close to the ground 7.

Weather and Climate

The Joshua Tree National Park has a arid, desert climate 1. This is because it is at roughly 30 degrees latitude, which is a worldwide zone of high pressure. The air at the equator rises and diverges above the surface to travel north or south of the Equator because it recieves direct insolation from the sun, making it hot and unstable. However, when it rises at the Equator, the humid air mass cools, and the relative humidity increases to dew point, for cool air has a lower capacity for water vapor 7. Then, if there are condensation nuclei in the air, clouds form above the equator and all of the humidity in the air is dumped out. Once the tropical air mass reaches about 30 degrees latitude, it starts to sink, warm, and form a high-pressure zone. Since warm air has a greater capacity for water vapor, the relative humidity decreases. Also, since the air is dry because it already rid itself of its humidity, it almost never reaches dew point to form clouds and rain 3. Joshua Tree National Park is also what is called a rain shadow desert because it is on the leeward side of the mountains near the California coast 1. When the maritime air masses come off the ocean and reach the mountains, they are forced upward due to orographic lifting 7. As they rise, they expand and cool, and their relative humidity increases to dew point. At this point, they form clouds and rain. Then, when they get over the mountains, the air masses are now dry, and they sink because there is no landform forcing them upward. Again, as these air masses sink, their relative humidity decreases, so they almost never form clouds and precipitation. This is another reason why Joshua Tree has a desert climate. On average, there is less than 25% humidity per day at Joshua Tree, and it only recieves an average of 4.06 inches of rain annually 4. The rain mostly falls in the higher elevated regions of the park where it does not evaporate before reaching the ground. Like other desert climates, Joshua Tree Park has very hot summers, with temperatures that can climb over 100 degrees Fahrenheit during the day. At night, the temperature can drop down to 75 degrees 8. This is because land is able to absorb heat quickly as opposed to water, but when the heat source vanishes, it is not able to retain its heat. During the winter, temperatures average about 60 degrees Fahrenheit per day. At night, it can drop down to 32 degrees. High elevations do receive minimal amounts of snow in the winter. The sun shines down on Joshua Tree park for about 230 days per year 8. As one travels through the park, they are likely to feel a light wind, averaging at about 6.6 miles per hour. During the winter, Joshua Tree National Park receives a minimum of 8 hours per day, while during the summer, the park receives a maximum of 19 hours of sunshine 8. The terrain of Joshua Tree is shaped by strong winds, sudden rains, and climactic extremes charateristic of a desert. The park rests on the edges of two deserts, the Mojave and the Colorado, which is part of the larger Sonoran Desert. The Colorado Desert is characterized by its lower elevations under 3,000 ft, and the multitude of Cresote bushes. The Mojave desert is the higher of the two, which renders the climate to be slightly cooler and wetter. This is the section of the park where the Joshua Trees thrive, characteristic of its name 3.

Flora and Fauna of Joshua Tree Since the desert climate is so harsh, the plants and animals of the park have learned to make some necessary adaptations for their survival. Common characteristics of animals include ones that can borrow underground to save themselves from the temperature extremes, and ones that don’t need much water to survive or can receive enough of it through the plants that they eat. Most of the animals' hair or fur have is light colored so that their coats do not absorb as much of the sun’s rays. Many desert animals are also nocturnal so that they do not have to bear the heat of the day. Other animals, like birds, have the ability to fly to water sources 1 . Common animal types include reptiles, small mammals, birds, and insects, spiders and centipedes. Mammals have the worst time living in the desert because their body temperatures cannot change. So, to adapt, most mammals have long limbs so that the heat can be distributed. The typical desert mammal is a small rodent. The kangaroo rat is one of the best mammals suited for this environment; it does not have to drink water at all during its life. Bats and kit foxes are nocturnal animals that prowl the desert at night, and bighorn sheep are easily able to navigate around the rocky terrain with their large cloven hooves 3 . Insects and spiders have exoskeletons to protect them from the heat, and they also can burrow under rocks. Since these small animals are common prey, they often are equipped with defense mechanisms: the giant hairy scorpion as poison in its stinger to defend itself against predators, and the tarantula has hair that it can shoot off into its enemies’ eyes 3 . Reptiles are very well suited to the desert biome because they do not have to produce their own body heat through food. This means that they do not need water for cooling; they just have to get out of the sun. Snakes, lizards, and a type of tortoise populate the park 3 .

Common desert plants must adapt to the harsh environment, as well. To do this, they often do not have leaves, because leaves provide surface area for transpiration to occur. Instead, they often have spikes or flowers. Desert plants take a while to grow because they have such limited nourishment resources, so the spikes serve as a defense and help them survive for a long time1 . Plants like cacti are also able to store water in their stems. These plants also typically have a dense covering of hairs or a thick, waxy covering to prevent water loss. The hairs are especially unique because they restrict the air flow around the plant to further prevent water loss. Most desert plants have an extensive root system just below the surface so that they can absorb nutrients as soon as they enter the ground 1 . Plants in the Colorado Desert include mesquite, desert holly, ocotillo, and teddy bear cholla. In the Mojave Desert, there is the yucca plant and the Joshua tree 3 .

A Park Without its Namesake

The climate of this picturesque park is changing for the worse due to the effects of global warming 10. Joshua Tree has been plagued by more frequent fires and drought, which is killing off the sensitive trees for which the park is named. While there used to be large fires every 50 to 100 years, they now occur every 3 to 10 years. The worst fire that Joshua Tree has seen occurred in 1999, named the Juniper complex fire. It was triggered by a lightening strike, and it burned up 14,000 acres of Junipers, Pines, Scrub Oaks, and Joshua Trees.

The fires are fueled by non-native ground cover grasses that proliferate in the park 10. These grasses feed on the car emission elements in the soil, so as the level of human pollution increases, the foreign grasses multiply quickly and feed fires. The Joshua trees burn up, and they barely ever reproduce—a deathly combination for the species. Yet, it is not only the loss of the trees that is devastating: the yucca night lizard makes its home in the roots of the Joshua trees, the Scott’s orioles build hanging nests amongst its branches, and the small desert rodents eat the tree’s seed pods and carry them to places where they can grow into new trees 10. Other negative human impacts on the park include crushed wildlife due to humans walking off trails and human trash buried by animals in the park 8.

<span style="display: block; font-family: Times New Roman; font-size: 12pt; line-height: 200%; text-align: center;">Works Cited 1) "Deserts." //Marietta College//. Web. 09 June 2010. <http://www.marietta.edu/~biol/biomes/desert.htm>. // 2) Joshua Tree National Park, California, United States //. Web. 09 June 2010. <http://www.gaisma.com/en/location/joshua-tree-national-park-california.html>. 3) "Joshua Tree National Park (U.S. National Park Service)." //U.S. National Park Service - Experience Your America//. 4 June 2010. Web. 09 June 2010. <http://www.nps.gov/jotr/index.htm>.4) "ProTrails: Wildlife Joshua Tree National Park, California." //ProTrails.com: Trail Database - Hiking Trails - Mountain Biking Trails - Mountain Climbing Access - Horse Trails//. 2003. Web. 09 June 2010. <http://www.protrails.com/area.php?areaID=24&subid=5>.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">5) “Sonoran Desert” //DesertUSA.com// Web. 1996. June 2010. <http://www.desertusa.com/jtree/jmap.html>. 6) “Sonoran Desert.” //NewWorldEncyclopedia.com// Web. 8 April 2008. June 2010. <http://www.newworldencyclopedia.org/entry/Sonoran_Desert>. 7) Tarbuck, Edward J., and Frederick K. Lutgens. //Prentice Hall Earth Science//. Needham, Mass.: Pearson/Prentice Hall, 2009. Print. 8) Uhler, John William. "Joshua Tree National Park." //Joshua Tree National Park//. 2007. Web. 09 June 2010. <http://www.joshua.tree.national-park.com/>. 9) “Wonderland of Rocks Traverse Trail.” //Trails.com// Web. 1999. June 2010. <http://www.trails.com/tcatalog_trail.aspx?trailid=HGS241-042>. 10) Zimmerman, Janet. "Desert Icon Joshua Trees Are Vanishing, Scientists Say | Riverside." //PE.com | Southern California News | News for Inland Southern California//. 20 June 2009. Web. 09 June 2010. <http://www.pe.com/localnews/environment/stories/PE_News_Local_S_joshuatree21.474c058.html>.