• Sunrise at the Cholla Cactus Garden

    Joshua Tree

    National Park California

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  • Pinto Basin Road Under Construction; Expect travel delays up to 30-minutes

    The ongoing construction project to improve Pinto Basin Road will impact travel between the northern portion of the park and the Cottonwood/I-10 area. Please plan accordingly. The project is expected to be completed in August 2014. More »

  • Deteriorating conditions of Black Rock Canyon Road

    The road leading to Black Rock campground has deep potholes, is deeply rutted, and can be difficult to negotiate, especially in large vehicles. Please drive with caution.

  • Access to some Cottonwood trails remains closed

    Trail access remains closed to Cottonwood Spring Oasis, Lost Palms Oasis, and Mastodon Peak. More »

Deserts

Some sources define a desert as an area receiving no more than ten inches of precipitation annually. However, many areas receiving this amount of precipitation are not deserts. This definition is not complete. Both the timing and type of precipitation determine the environment established.

In a desert, rain isn’t evenly distributed throughout the year. Weather patterns often create short, violent downpours that produce flash floods. Much of the water runs off before it can soak into the soil. A lot of moisture is also lost to evaporation.

Many deserts lie in areas of high pressure systems where there is little cloud cover. At least 90 percent of the sun’s rays reaches Earth’s surface, producing seasonal hot temperatures. (For comparison, the surface of more humid lands, covered with more vegetation, receives only 40 percent of possible solar radiation.) The hot, dry air causes any available water to evaporate quickly.

When temperatures are extremely hot, rain can evaporate before it reaches Earth. The conditions producing high daytime temperatures reverse the process after sundown. Approximately 90 percent of the day’s accumulated heat radiates back toward the sky. (In moister climates only about 50 percent of this heat is lost.) These conditions produce the wide range of daily temperatures characteristic of deserts. This range is often 50 degrees or more.

The rapid heating and cooling of air create another characteristic of most deserts: strong winds. These winds, circulating air that is often hot and dry, increase the already high rate of evaporation. Evaporation in American deserts ranges from 70 to 160 inches per year.

A desert then is not so simply defined. Several characteristics: seasonal, high temperatures; low, sporadic rainfall; a high rate of evaporation; wide temperature ranges; and strong winds are part of the definition.

Did You Know?

Fault map of the park

Joshua Tree is crisscrossed with hundreds of faults, and is a great place to see raw rocks and the effects of earthquakes. The famous San Andreas Fault bounds the south side of the park and can be observed from Keys View. More...