This Land: California

Natural History, March, 2000 by Robert H. Mohlenbrock

Four major deserts lie in the long trough between the Rocky Mountains and the Sierra Nevada and Coast Ranges of North America: the Great Basin, the Mojave, the Chihuahuan, and the Sonoran. Occupying elevations of up to about 3,000 feet in much of southeastern California and parts of southwestern Arizona, with extensions into Baja California and other parts of Mexico, the Sonoran has several natural divisions. The westernmost section, in California, is bounded on the east by the Colorado River and is usually referred to as the Colorado Desert. It is watered by gentle winter rains from the Pacific Ocean and more violent summer storms that blow in from the Gulf of Mexico.

Low desert--the sandy fiats found in valleys and bordering the many mountains--is the principal habitat in the Colorado Desert. Traversing this landscape are countless washes--waterways that are dry for most of the year but fill up briefly following torrential summer rains. The low desert also has some scattered palm oases, alkaline sinks, desert marshes, and permanent streams. The often steep and rugged lower slopes of the mountains are dominated by cacti, agaves, yuccas, and thorn-bearing shrubs. Farther upland, usually between 3,000 and 5,000 feet, is chaparral, where scrub oaks, manzanitas, and various other shrubs join cacti and yuccas.

One of the best places to explore the Colorado Desert is Anza-Borrego Desert State Park, a 1,500-square-mile preserve that has well-paved roads and miles of primitive jeep trails and hiking trails. Among the paved roads is Highway S22, which passes through typical low desert as well as a severely eroded landscape known as the Borrego Badlands. Thimble Trail, off S22 in the badlands, is an excellent place to see the colorful annual wildflower show that appears (if winter rainfall has been ample) between mid-February and early April. Anywhere a paved road crosses one of the normally dry washes is a good place to study desert-wash vegetation. One such location is Smoke Tree Canyon, which is easily accessible from S22 and has a concentration of smoke tree (Psorothamnus spinosa) as well as indigobush (P. schottii) and desert lavender. A fine chaparral community can be viewed along S22 as it passes through Culp Valley, southwest of the desert community of Borrego Springs.

The lower slopes of the mountains that rise from the desert floor are often difficult to hike because of the rocky terrain. But a typical (and easily reachable) patch of this kind of desert habitat lies near Ocotillo Flats and can be reached by taking DiGiorgio Road north out of Borrego Springs and continuing along a dirt road. This is a good place to encounter the purple milkweed vine Sarcostemma and the lavender-flowered spectacle pod, a member of the mustard family.

The goal of many park visitors is to see Washington fan palms, which grow naturally only in California's Colorado Desert and in two isolated spots in western Arizona. The sixty-foot trees live in patches kept wet by underground water sources. Reaching these oases usually requires a hike through rocky ravines; the easiest to get to is Borrego Palm Canyon, just one and a half miles by hiking trail from the nearby campground. Another unusual plant is the elephant tree, named for its swollen gray trunk and limbs. The most accessible ones grow a short distance from the Elephant Tree parking area off Split Mountain Road.

Among Anza-Borrego's wetlands is Coyote Creek, a perennial stream in the northwest corner of the park. Its rugged surroundings may be explored on foot or partway by jeep. Plants that grow along the stream banks include alder, Fremont cottonwood, sycamore, honey mesquite, and Goodding willow. Another wetland is the marshy Sentenac Cienega, along San Felipe Creek, near the juncture of Routes 78 and S2. The huge reed Phragmites grows there, along with three-square, a sedge found in wetlands across the United States. Woody plants along the margins include Goodding, narrow-leaved, and arroyo willows; Baccharis; desert willow (not a willow but a relative of the catalpa tree); and Fremont cottonwood.

Scattered depressions in the desert fill with water after a rainfall, retaining an alkaline residue as the water evaporates. One of these alkaline sinks is Borrego Sink, about five miles southeast of Borrego Springs. Most of the plants found here can tolerate a high degree of salinity and, apart from the honey mesquite, do not grow elsewhere in the park. Among them are salt grass, pickleweed (also called samphire, or Salicornia), arrowweed (a purplish-flowered perennial related to the marsh fleabane of the southeastern United States), and several species of Atriplex, or saltbush.

For visitor information, write: Anza-Borrego Desert State Park 200 Palm Canyon Drive Borrego Springs, CA 92004 (760) 767-4205 www.anzaborrego.statepark.org

Robert H. Mohlenbrock, professor emeritus of plant biology at Southern Illinois University, Carbondale, explores the biological and geological highlights of U.S. national forests and other parklands.