Up Above: The Geography of Suburban Sprawl
in Southern California’s Antelope Valley

Matthew Jalbert

It is the Antelope Valley’s physical character which first impresses the observer. It is a vast, nearly flat space of coalesced alluvial fans washed down over millennia from the surrounding mountains. On the southern border lay two mountain ranges: the Sierra Pelonas, which give way to the gnarled San Gabriels at Soledad Pass (which, in cleaving the two ranges, marks the Antelope Valley’s midpoint) and continuing far to the east. The northern boundary of the Antelope Valley is the long-recognized boundary of Southern California itself—the Tehachapi Mountains, far lower in elevation than the opposing San Gabriels. These mountains meet at the Valley’s western tip, forming the well-defined point of a triangle. Together, the ranges account for the Valley’s desert climate. Contrary to one real estate huckster’s assertion that “the natural funnel produced by the converging Tehachapi and San Gabriel mountain ranges aids rainfall,” [Footnote #1] the immense Mojave Desert begins with the Antelope Valley, progeny of a huge rainshadow left by Southern California’s Transverse ranges.

Mary Austin, writing with a disdain for the landscape characteristic of her era in Land of Little Rain (1903), noted the physical character of the point where these mountains meet and the desert which emanates from there:

Nothing the desert produces expresses it better than the unhappy growth of the tree yuccas. Tormented, thin forests of it stalk drearily in the high mesas, particularly in that triangular slip that fans out eastward from the meeting of the Sierras and coastwise hills where the first swings across the southern end of the San Joaquin Valley. [note #2]

The “tree yuccas” Austin describes are the Joshua trees (Yucca brevifolia) which, along with creosote bush, rabbitbrush, and juniper, compose the visually dominant vegetation of the undeveloped plains. The “triangular slip that fans out eastward” is, indeed, the Antelope Valley, whose triangular shape forms the western element of the Mojave desert.

The Antelope Valley is often described as “high desert,” accounting for the elevations of around 3050 feet in its southern foothills to the playas of Rosamond and Rogers Dry Lakes at about 2270 feet. The whole floor of the valley is inclined down toward the north until it inches up again toward the Tehachapis. Several exfoliated granite buttes—with names such as Fairmont, Little, Saddleback, Piute, and Lovejoy—dot the valley. Their widely scattered positions constitute infrequent relief on the horizon before the mountains arise. To the east, a loose constellation of buttes marks the boundary of the Antelope Valley near the Los Angeles–San Bernardino County line. [note #3]

A Joshua tree in the Antelope Valley.

As high desert, the Antelope Valley experiences a much different climate than the nearby coastal plains. Separated by mountains from the moderating effects of marine air, the Antelope Valley has a more “continental” climate, marked by wide diurnal and seasonal temperature variations. Winter nights often drop below freezing, and snow is not unheard of. Daytimes are warm, with a January average of 56° F and a July average of 98°. [note #4] Strong wind is one of the Valley’s constants, occasionally whipping up dust and sand storms. Like all deserts, the Valley’s rainfall is slight: from five to nine inches fall annually, with the southern edge’s higher foothills receiving more precipitation than the drier, lower plains. [note #5] California’s Mediterranean climate characterizes the Valley, with rainy winters and long, dry summers.

The heat of late summer and fall are sometimes punctuated by huge cloudbursts. In extreme cases, flooding has occurred when a year’s total average rainfall was received in one storm. If this sudden runoff fails to find adequate channels and instead spreads out across the desert floor, sheet flooding occurs. What water is not absorbed in the gravels and sands will pond in the beds of Rosamond and Rogers Dry Lakes at the Valley’s northern edge, where it eventually evaporates. As an enclosed basin with no outlet to the sea, the Antelope Valley has experienced “severe” or “extensive” flooding in at least nine of the past fifty-six years. [note #6] Much of this is due to rainfall in the adjacent San Gabriel Mountains, where annual precipitation is on the order of 20–40 inches. A single storm may deposit much of this, with consequential rapid runoff and flooding on the Valley floor.

Earthquakes are even more potentially catastrophic to the Antelope Valley than flooding. The Antelope Valley was literally made by tectonic action—the northern edge’s Tehachapis were uplifted by the action of the Garlock fault, and the steep rise of the San Gabriels occurs where the vaunted San Andreas Fault passes along the Valley’s southern edge. Indeed, the San Andreas forms the boundary between the North American continental plate on which the Antelope Valley sits, and the geologically distinct Pacific Plate on which the Los Angeles Basin sits. Four subsidiary faults, branches of the San Andreas, surround the Antelope Valley. In 1857, the massive Fort Tejon earthquake ruptured the San Andreas and displaced the plates by twenty feet in the Antelope Valley area. The scarp left by this quake is a major attraction for geologists. Climbing it, one can look into the roadcut where the Antelope Valley freeway passes through the scarp and see for oneself the terrifically deformed rock featured in so many geology textbooks. [note #7] Geologists expect another great earthquake on the San Andreas of similar magnitude to 1857’s 8.0+ within twenty-five years. The much-discussed “Big One” is likely to happen right in the Antelope Valley’s front yard.

NEXT | Americans, Alfalfa, and the Antelope Valley

© Matthew Jalbert 1995–2002