Joshua Tree National Park
The desert is immense and infinitely variable, yet delicately fragile. It is a land shaped by sudden torrents of rain and climatic extremes. Rainfall is sparse and unpredictable. Streambeds are usually dry and waterholes are few. This land may appear defeated and dead, but within its parched environment are intricate living systems, each fragment performing a slightly different function, and each fragment depending upon the whole system for survival.
The vegetation in the area varies with the topography, elevation, and gradient. It is estimated that more than 850 plant species live in the park (Adams 1957). Below 3,000 feet, the Colorado Desert (or low desert) is dominated by creosote bush, mesquite, yucca, ocotillo, and species of cactus. Whenever moisture conditions are favorable, cat's claw, palo verde, and desert willow may also appear. In Pinto Basin, creosote bush, white burro weed, several species of grass, and many species of cactus grow. Occasional sand dunes or basins of loose sand provide a rare habitat in this desert most often dominated by annual grasses following spring rain.
Above 3,000 feet three basic vegetation associations have been classified (Holland 1986):
Mojave mixed steppe - Joshua trees, galleta grass, needle grass
Blackbrush scrub - blackbrush, Mojave yucca, Joshua tree, California juniper
Mojavean pinyon/juniper woodland - pinon pine, scrub oak, California juniper
The Mojave Desert is biologically more diverse than the Colorado Desert, probably due to greater precipitation. In the Mojave, mixed steppe densities of Joshua trees vary dramatically. The thickest forests are in Covington Flats, Lost Horse, and Queen Valley areas.
The transition zones between the two deserts provide for an increased biodiversity. They are typically dominated by common shrubs such as desert senna, bladder pod, jojoba, desert mallow, paper bag bush, encelia, vigueria, whiteratany, and four-o'clock. Other shrubs in these areas include jimsonweed and coyote melon. After adequate rainfall the deserts can be transformed by colorful wildflower displays, including extensive areas of Bigelow coreopsis, sand verbena, phacelia, evening primrose, blazing star, pincushion, chia, and others. Fanpalm oases also appear in the park, primarily in the Colorado Desert portion in the Cottonwood area. A few groves are in the southwest portion of the Mojave Desert, close to Indian Cove and at the headquarters at Twentynine Palms.
Species of Special Concern
The following is a list of endangered, threatened, and candidate plant and animal species that may exist in Joshua Tree National Park. This list was included in a letter dated January 21, 1997 from the U.S. Fish and Wildlife Service. The species listed are known to occur in or near the park. Two additional species are included below that are not on the U.S. Fish and Wildlife Service list but are of special interest to the National Park Service.
One plant species is listed as endangered, the Cushenberry milk-vetch (Astralegus albens). The following plants are proposed endangered (PE) or proposed threatened (PT):
Munz's onion (Allium munzii) - PE
triple-ribbed milk-vetch (Astragalus tricarinatus) - PE
Pierson's milk-vetch (Astragalus magdalenae var. piersonii) - PE
Nevin's barberry (Berberis nevinii) - PE
thread-leaved brodiaea (Brodiaea filifolia) - PT
In addition to listed species, the Joshua tree (Yucca brevifolia) and the California fan palm (Washingtonia filifera) are species of special interest in the park.
Groundwater follows zones of least resistance along deeply fractured rock masses and deep loose gravel. There are very few known water tables near the surface. Rainfall is inadequate to recharge underground water. Surface water flows out of the area without percolating into the park's aquifer. By far the largest amount of groundwater is in the Pinto Basin, one of the extensively alluvial valleys underlying the eastern portion of the park. The U.S. Geological Survey estimates that this basin could yield 300,000 acre-feet per year of water in the upper 100 feet of the saturated zone.
Naturally occurring water is rare in the park. There are over 120 known water sources, including springs, seeps, wells, and one short perennial stream. Flows from springs and seeps range from seasonal dampness to about seven gallons per minute. The majority of the springs flow from fractures and joints in the igneous and metamorphic basement complex and appear to be supported by local aquifers. Past monitoring indicates that discharge at some springs is decreasing, and compared to historic accounts, surface water has decreased significantly from 50 years ago. The cause is uncertain and may be attributable to climate change, changes in vegetation, sampling error, water pumping and use, or natural variation.
Several oases, encircled by California fan palms, are found in the park and provide a dramatic contrast to their surroundings. They symbolize the importance of water in shaping the landscape and sustaining life in the desert.
Three artificial impoundments (Barker Dam, Cow Camp, and Keys Lake) contain significant amounts of water most years. These dams were constructed to supply water for ranching and are now considered eligible for listing on the National Register of Historic Places. The dams also provide an artificial source of water for native and exotic wildlife.
California desert environments have traditionally been viewed as wastelands by some people, and the park has been damaged and abused because many users are not aware of their fragile nature. The counties within a 100-mile radius of the park are Los Angeles, Orange, Riverside, San Bernardino, Imperial, and San Diego. These counties contain more than 18 million people, and the population is growing. Over ten million acres of federal and state land in these counties are available for recreation.
Some land adjacent to the park has been subdivided into small desert communities for homesites. Morongo Valley, which parallels most of the park's north boundary, is almost completely subdivided into homesites and desert homesteads. Other desert homesites extend along the southwestern boundary along the foot of the Little San Bernardino Mountains. Farther to the south lies the sea level Coachella Valley, an irrigated agricultural area of date palms, vineyards, and citrus groves. The valley is the site of Palm Springs, an internationally recognized destination resort. The mountainous portions along the boundaries are largely in the public domain, where the primary use is vehicle-oriented recreation and BLM-administered wilderness (Sheephole) and one area of critical environmental concern (Big Morongo). The largest area of mining claims and associated mining-related disturbance near the park is the Eagle Mountain Mine area, which is in a salient that is surrounded on three sides by the park. The area is the subject of a controversial proposal for the world's largest landfill.
The landfill would include the open mining pits in the Eagle Mountain mine area. Its proximity poses some obvious threats to the adjacent wilderness. Blowing trash, dust, noise, and odors could impair the fragile setting. The operations would present other, less obvious, threats to the natural ecosystem. Household trash attracts scavengers such as ravens and coyotes, which can flourish in such a setting. Ravens are known to eat young tortoises. The largest known population of tortoises in the park is within six miles of the proposed landfill.
The abandoned open pits continue to attract other development proposals. If the landfill does not go forward, there is a proposal to fill the pits with water for use in a hydroelectric scheme.
The proximity of Joshua Tree National Park to the Los Angeles metropolitan area and to a large military base generates a steady flow of visitors. The recreational demands of southern California are enormous. For people who are subjected to automobile congestion, air pollution, and disappearing open space, the desert offers rest and relaxation, fresh air, clear skies, outdoor recreation, solitude, and contemplation. Many return frequently for specific recreational activities.
Urbanization and incompatible land uses along the boundary can cause profound deterioration of resources. Examples include air pollution, groundwater pumping and depletion, noise and light pollution, alteration of natural systems along the boundary, incursion of domestic pets into the park, and visual intrusions.
Details mentioned in this article were accurate at the time of publication