Jeffrey pines in the Laguna Mountains

      The San Gabriel Mountains

      Turning our attention farther north and east, we find the San Gabriel Mountains, another segment of the east-west-trending Transverse Ranges. Behind the south ramparts of the San Gabriels, whose chaparraled slopes rise sheer from the Los Angeles Basin and the San Gabriel Valley, stands a series of high peaks, the tallest of which—Old Baldy, also known as Mt. San Antonio—exceeds 10,000 feet in elevation. Yawning gorges slash into the range, in one place offering more than a mile of vertical relief between canyon bottom and adjacent ridge.

      Geologists figure that the San Gabriels are being squeezed horizontally about a tenth of an inch each year, and being thrust upward much more rapidly than that. Caught in this tectonic frenzy, the San Gabriel Mountains are surging upward as fast as any mountain range on the planet. They are also disintegrating at a spectacular rate. Although the San Gabriels consist mainly of durable granitic rocks, much like those in the sturdy Sierra Nevada, the San Gabriel rocks have been through a tectonic meat grinder. The tops of the San Gabriels are fairly rounded, but their slopes are often appallingly steep and unstable. An average of 7 tons of material disappears from each acre of the front face each year, most of it coming to rest behind debris barriers and dams in the L.A. Basin below.

      The San Gabriel Mountains themselves are relatively young as upthrust units—only a few million years old. This is not true of the ages of most of the rocks that compose them. Some rocks exposed here are representative of the oldest found on the Pacific Coast—more than 600 million years old.

      Botanically, parts of the San Gabriel Mountains are extremely attractive, especially in zones above 4,000 feet that receive enough precipitation. There the coniferous forest, which has two phases in Southern California, thrives. The yellow pine phase includes conifers such as bigcone Douglas-fir, ponderosa pine, Jeffrey pine, sugar pine, incense-cedar, and white fir, and forms tall, open forest. These species are often intermixed with live oaks, California bay (bay laurel), and scattered chaparral shrubs such as manzanita and mountain mahogany. Higher than about 8,000 feet, in the lodgepole pine phase, lodgepole pine, white fir, and limber pine are the prevailing trees. These trees, somewhat shorter and more weather-beaten than those below, exist in small, sometimes dense stands, interspersed with such shrubs as chinquapin, snowbrush, and manzanita.

      Excluding relatively small parcels of private land, the bulk of the higher San Gabriel Mountains lies within Angeles National Forest. Hundreds of square miles of wilderness or near wilderness in the San Gabriels are available within easy reach of millions of L.A. residents.

      The 2009 Station Fire devastated the western portion of the San Gabriel Mountains, charring more than 160,000 acres. More than three years later, many affected areas remain closed to aid recovery, while others are open but will be scarred for decades.

      The San Bernardino Mountains

      Farther east, across the low gap of Cajon Pass, the Transverse Ranges soar again as the San Bernardino Mountains. With Lake Arrowhead, Big Bear Lake, and winter ski areas, the mid-elevations of the San Bernardinos (5,000–8,000 feet in elevation) draw millions of day-trippers and vacationers annually. Hikers and backpackers can explore the 10,000-foot-plus peaks of the San Gorgonio Wilderness, including 11,500-foot San Gorgonio Mountain itself—Southern California’s high point. There it is possible to ascend through the yellow-pine and lodgepole belts to treeline and above.

      As in the San Gabriel Mountains, islands of private land in the San Bernardinos are surrounded by large sections of national forest. San Bernardino National Forest encompasses much of the San Bernardino Mountains, as well as the San Jacinto and Santa Rosa Mountains to the south.

      The most dramatic change taking place in the high mountains of Southern California—especially the San Bernardinos —is a massive die-off of coniferous trees. The high-elevation areas in Southern California have been receiving less precipitation in recent decades. A string of very dry years beginning in 1998–99 triggered an acute infestation of bark beetles, which eventually resulted in sudden death for millions of drought-stressed pine, fir, and cedar trees. Wildfires in October 2003 and 2007 destroyed millions of these dead and dying trees, and many others are being removed by logging operations in an overall effort to thin the forest to attain a more healthy level of tree density.

      The Mojave Desert

      North and east of the San Gabriel and San Bernardino Mountains lies the vast, arid sweep of the Mojave Desert, a zone only partly included in this book. The Mojave, sometimes known as the high desert for its generally high average elevation, becomes far less populated and more diverse in its natural features as we move toward eastern California. A few of the hikes in this book explore the transitional region between high mountain and high desert.