A large part of Southern California is desert. And much of the rest of Southern California is “semi-arid:” It gets more rainfall than an actual desert, but not enough to support a large human population without importing substantial amounts of water from elsewhere. The entire densely-populated region stretching from Santa Barbara in the north through Los Angeles to San Diego in the south is all too frequently subject to severe droughts. It depends on major engineering projects that divert water from the eastern Sierra Nevada region and the Colorado River.

Two national parks in this large desert region offer unique geology, biology, and scenery. Joshua Tree National Park is in the southern desert north of Palm Springs. Death Valley National Park is in eastern part of the state, on the Nevada border (a small part of the park is in Nevada).

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Joshua Tree National Park’s nearly 3200 square kilometers include two distinct California deserts. The Colorado is “low desert,” at elevations from 275 meters up to 915 meters. The drier, cooler Mojave is “high desert,” at elevations from 915 to 1800 meters.

The “forest” of Joshua trees in the Mojave high desert section gives the park its name. Even though it has a woody trunk and branches, the Joshua tree isn’t a tree at all. It’s actually a kind of yucca, in the same botanical family as the Mexican agave plant whose sap is fermented and distilled into tequila. Nineteenth-century miners and ranchers, in apparent ignorance of botany, burned the trunks and branches for fuel and also made fences out of them. I am not aware of any intoxicating use of these yuccas, though I’m sure those miners and ranchers tried their best.

Mormon pioneers encountered these unusual trees during their extensive travels in the Southwestern desert to escape religious persecution. Steeped in biblical lore, the Mormons saw the trees as the prophet Joshua praying with arms stretched to heaven as he led the Israelites to the Promised Land.

The low Colorado Desert is the realm of cactus, particularly the cholla (“CHOY-a”). From a distance, cholla looks so cute and cuddly that it’s sometimes even called the “teddy bear cactus.” But close up, it’s anything but cuddly. It will attack the unwary with a nasty bite. The “fur” is actually very prickly spines with little barbs at the end. Get anywhere near one with your hand, or even with a clothed arm or leg, and the little barbs will attach themselves painfully to your flesh. The barbed spines are an effective defense against any lizards, birds, or rodents that might fancy a snack.

Cholla barbs get into inappropriate places so easily that the other nickname for the cholla is the “jumping cactus.” It almost seems to jump right for the nearest arm or leg. When taking these pictures, I was very careful to avoid touching the cholla. But somehow a little cluster jumped onto the bottom of my camera bag. Removing it required a thick wad of newspaper.

Although the park was named for its distinctive flora, the yuccas, cactus, and desert diversity aren’t what make the park popular with visitors from all over the world. Joshua Tree is far better known for its rock formations, the product of an unusual combination of geological processes. Rock climbers and bouldering enthusiasts at “JT” can choose from over 400 formations, and some 8,000 named climbing routes.

The jumbled piles of enormous, sometimes precariously balanced boulders look like some kind of implausible construction project, perhaps abandoned by ancient alien astronauts. But no science-fiction explanation is needed when you’ve got geology and millions of years for nature to do the job.

Dinosaurs might have found this area inhospitable. It wasn’t a desert in those days, but there was a lot of volcanic activity. The columns of magma that welled up underground began to crack into blocks as they cooled. Since the climate was much wetter then, rainwater seeped underground and percolated through the volcanic rock. Over millions of years, that water eroded the rectangular blocks into spheres.

The climate change to desert shut off the percolator. The rain that does come to the desert is brief but torrential, creating intense flash floods. Over the years, the powerful floods first exposed the eroded volcanic rocks and then carried them away, depositing them into the heaped formations seen today.

The earthquakes for which California is renowned continue to put the finishing touches on the job begun by volcanoes and water. The famous San Andreas Fault is the park’s southern boundary; the Pinto Mountain fault is just to the north, and the Blue Cult Fault bisects the park. There are also hundreds of small unnamed faults throughout the park. These faults continuously produce earthquakes that only seismographs can “feel,” but there’s a good chance of experiencing one or more larger ones, as I did.

The ocotillo (“oak-o-TEE-yo”) is another distinctive denizen of the low desert. Although it’s often called a cactus, it’s actually not in that family. Much of the time the ocotillo looks like an oversized upended scraggly broom, with seemingly dead brown woody bristles sprouting from the ground. But after a heavy rain it quickly comes to life, with red flowers and small tough leaves that minimize evaporation of water into the dry air. This blooming ocotillo is in Anza-Borrego Desert State Park, in the low desert south of Joshua Tree.

The Coachella Valley, in the low desert south and east of Joshua Tree, is a major producer of dates. Not surprisingly, the local culinary speciality is the “date shake,” a vanilla milkshake flavored with puréed dates. This cultivated stand of date palms is in the town of Mecca. The fruit grows in clusters on the palms.

As far as I know, the Mecca in California in no way resembles its Arabian namesake; it’s mainly a community of migrant farm workers. So my visit there in no way entitles me to the honorific title of “Haji.” There was, however, a pillar of fire and black smoke guiding me toward Mecca. It turned out to be from an incineration facility that was burning worn-out tires.

At the southern end of the Coachella Valley, the Salton Sea was created by accident around 1905, when poorly-built irrigation channels flooded an ancient basin. It’s the largest lake in California, 57 kilometers long and 24 kilometers wide. The surface is 69 meters below sea level. Like Mono Lake in northern California, the Salton Sea has no outlets, so it is becoming increasingly salty (it is now about 25% saltier than the ocean). It’s also a migratory bird sanctuary as well as a popular boating recreation area. Unlike Mono Lake, some 90% of the Salton Sea’s water comes from agricultural runoff. The pesticides and heavy metals in this runoff make the lake controversial for environmentalists. On a hot May weekday, I found the Salton Sea a rather desolate and strangely alien setting.

The fine print: All pictures and text are copyright ©  1991, 1998, and 2010 by Ted R. Marcus and may not be reproduced without permission. For information about licensing any of these images for Web, print, stock, or other uses, contact me.