Joshua Tree National Park encompasses some of the most interesting geological displays one could hope to see. With more than half a million acres of wilderness it is a huge National Park. Located about two hours east of Los Angeles, California, it is beyond the Santa Rosa and San Jacinta Mountains. It is part of the Mojave Desert.
Rugged mountains, uplifted strata of folded granite, twisted and eroded rock, and exposed granite monoliths are visible evidence of the powerful forces that have shaped the land in the Park.
No specialist geological training is needed to see plainly visible arroyos, playas, alluvial fans, and bajadas.
The Joshua Tree, Yucca brevifolia, is a member of the Agave family and is a close relative of the Mojave yucca, Yucca schidigera. Both types of yuccas can be seen growing together in the park.
The Joshua Tree provides a good indicator that you are in the Mojave Desert,
American Indians worked the leaves into baskets and sandals, and used the flower buds and raw or roasted seeds as part of their diet.
It is claimed that a group of Mormon settlers who crossed the Mojave Desert in the mid-19th century named the tree because its unique shape reminded them of a biblical story in which Joshua reaches his hands up to the sky in prayer. Ranchers and miners who were contemporary with the Mormon immigrants used the trunks and branches as fencing and for fuel for ore-processing steam engines.
Joshua trees are fast growers for the desert; new seedlings may grow at an average rate of 75 mm per year in their first ten years, then only about 40 mm per year thereafter. If it survives the rigors of the desert it can live for hundreds of years with some specimens surviving up to a thousand years. The tallest trees reach about 15 metres.
Joshua trees usually do not branch until after they bloom and they do not bloom every year. Like most desert plants, their blooming is dependent on rainfall at the proper time. They also need a winter freeze before they will bloom. Once they bloom, the trees are pollinated by the yucca moth which spreads pollen while laying her eggs inside the flower.
Getting a Different View
Keys View Lookout
The Keys View lookout is on the crest of the Little San Bernardino Mountains and offers fantastic panoramic views of the Coachella Valley, including the 1100 kilometre long San Andreas Fault.
The Santa Rosa Mountains, the San Jacinto Peak and usually-snow covered 3500 metres San Gorgonio Mountain are clearly visible from the lookout.
Ranchers utilised areas that are now part of the National Park. The rainfall averaged 250 mm in the late 1800s/early 1900s, suitable for raising cattle. Today, rainfall averages only 60 mm.
Barker Dam is an example of the water impoundments built by the cattlemen.
The National Park has more than 750 different types of plants.
As one descends towards the Cottonwood Visitor Centre the Joshua trees disappear and the Cholla Cactus Garden suddenly appears.
The Cholla Cactus is also called the Jumping Cactus, a name it received from the ease with which the stems detach when brushed, giving the impression that the stem jumped. The merest touch can leave a person with bits of cactus attached to them. The ground around a mature plant will often be covered with dead stems, and young plants are started from stems that have fallen from the adult. They attach themselves to desert animals and are dispersed for short distances.
Joshua Tree is crisscrossed with hundreds of faults. The effects of earthquakes and ‘raw rocks’ are easily seen. The famous San Andreas Fault bounds the south side of the park, and can be seen from the fantastic Keys View lookout.
Movement by faults causes impervious zones of shattered rock fragments to form an underground dam, forcing ground water to rise and creating a natural spring.
The park has five fault-caused palm oases that are an important supply of food and water to a wide variety of wildlife habitat.
California’s Colorado Desert
As we left Joshua Tree we were still in the Mojave Desert which is part of the California Colorado Desert, part of the bigger Sonoran Desert. The road towards Mecca in the Coachella Valley is routed through box canyons.
Groundwater and water transported via the Coachella Canal have transformed the desert environment into large swaths of agricultural land. The Coachella Valley has become one of the main agricultural production bases in the world. The warm year-round climate in the region and irrigation systems allows producers to cultivate a variety of fruits and vegetables.
The Salton Sea is a shallow, saline, rift lake 72 m below sea level, located directly on the San Andreas Fault in the Coachella Valley,
The modern Salton Sea was accidentally created by the engineers of the California Development Company in 1905. In an effort to increase water flow into the area for farming, irrigation canals were dug from the Colorado River into the valley. Due to fears of silt buildup, a cut was made in the bank of the Colorado River to further increase the water flow. The resulting outflow overwhelmed the engineered canal, and the river flowed into the Salton Basin for two years, filling the historic dry lake bed and creating the modern sea, before repairs were completed.
The surrounds of present day Salton Sea are impoverished and slum-like. It is disappointing when one considers what it once was and what it could still be.
We left the area via Palm Springs and headed back to Los Angeles.
© Kim Epton 2015-2019
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