Thursday, March 15, 2012

USA - California - Joshua Tree National Park

Joshua Tree is a rock-climbers paradise, providing beautiful vistas of the desert to those that scale these grand boulders. The geologic landscape of Joshua Tree has long fascinated visitors to this desert. These rocks, referred to as monzogranite, took on their fantastic shapes millions of years ago through the forces of volcanism and erosion.

Sent by The Colliers, postcrossers from California, USA.

This is from Wikipedia : Joshua Tree National Park is located in southeastern California. Declared a U.S. National Park in 1994 when the U.S. Congress passed the California Desert Protection Act (Public Law 103-433), it had previously been a U.S. National Monument since 1936. It is named for the Joshua tree (Yucca brevifolia) forests native to the park. It covers a land area of 790,636 acres (1,235.37 sq mi; 3,199.59 km2) – an area slightly larger than the state of Rhode Island. A large part of the park, some 429,690 acres (173,890 ha), is a designated wilderness area. Straddling the San Bernardino County/Riverside County border, the park includes parts of two deserts, each an ecosystem whose characteristics are determined primarily by elevation: the higher Mojave Desert and lower Colorado Desert. The Little San Bernardino Mountains run through the southwest edge of the park.

The higher and slightly cooler Mojave Desert is the special habitat of Yucca brevifolia, the Joshua tree for which the park is named. It occurs in patterns from dense forests to distantly spaced specimens. In addition to Joshua tree forests, the western part of the park includes some of the most interesting geologic displays found in California's deserts. The dominant geologic features of this landscape are hills of bare rock, usually broken up into loose boulders. These hills are popular amongst rock climbing and scrambling enthusiasts. The flatland between these hills is sparsely forested with Joshua trees. Together with the boulder piles and Skull Rock, the trees make the landscape otherworldly.

Joshua trees dominate the open spaces of the park, but in among the rock outcroppings are piñon pine, California juniper (Juniperus californica) and scrub oak. These communities are under some stress, however. The climate was wetter until the 1930s. The same hot and dry conditions that provoked the Dust Bowl affected the local climate. These cycles were nothing new, but the original vegetation did not prosper when wetter cycles returned, however. The difference may have been human development. Cattle grazing took out some of the natural cover and made it less resistant to the changes. But the bigger problem seems to be invasive species, such as cheatgrass. These things deliver a double punch. During wetter periods, they fill in below and among the pines and oak. In drier times, they die back, but do not quickly decompose. This makes wildfires hotter and more destructive, which kills some of the trees that would have otherwise survived. When the area regenerates, these non-native grasses form a thick layer of turf that makes it harder for the pine and oak seedlings to get a roothold.

Below 3,000 feet (910 m), the Colorado Desert encompasses the eastern part of the park and features habitats of Creosote bush scrub; Ocotillo, desert Saltbush and mixed scrub including Yucca and Cholla cactus (Cylindropuntia bigelovii). There are areas of such cactus density they appear as natural gardens. The lower Coachella Valley is on the southeastern side of the Park with sandy soil grasslands and desert dunes.

The only palm native to California, the California Fan Palm (Washingtonia filifera), occurs naturally in five oases in the park, rare areas where water occurs naturally year round and all forms of wildlife abound.

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