Geography
Much of the range features rolling peaks. The range lacks craggy features, but contains a large number of canyons and is generally very rugged and difficult to traverse. The San Gabriel Mountains are composed of a large fault block between the San Andreas Fault Zone to the north, and the San Gabriel Fault and the Sierra Madre-Cucamonga Fault Zones to the south. This tectonic block was uplifted during theSetting and elevation
The highest elevation, Mount San Antonio (Mount Baldy) at , rises towards the eastern extremity of the range which extends from the Cajon Pass (Interstate 15) on the east, where the San Gabriel Mountain Range meets the San Bernardino Mountain Range, westward to meet the Santa Susana Mountains at Newhall Pass (Interstate 5). South and east of Santa Clarita and north of San Fernando, the San Gabriel Mountains crest abruptly up to about . Pacoima and Big Tujunga Canyons cut through the range just east of San Fernando, carrying runoff into the San Fernando Valley. Little Tujunga Canyon Road bridges the range in this area, connecting the San Fernando Valley to the Santa Clara River valley in the north. Towering over Big Tujunga Canyon north of Big Tujunga Reservoir, and south of Acton, is Mount Gleason, which at , is the highest in this region of the San Gabriels. South of the gorge is the southern "foothills" of the mountains, which rise abruptly above the Los Angeles Basin and give rise to the Arroyo Seco, a tributary of theLocale
The Range is bounded on the north by the Antelope Valley and the Mojave Desert and to the south by the communities of Greater Los Angeles. The south side of the range is almost continuously urbanized and includes theHydrology
Melting snow and rain runoff on the south side of the San Gabriels' highest mountains give rise to its largest river, the San Gabriel River. Just to the west of Mount Hawkins, a north–south divide separates water running down the two main forks of the river and their tributaries. The West Fork, beginning at Red Box Saddle, runs eastward, and the East Fork, starting north of Mount San Antonio, flows south and west through a steep, rugged and precipitous gorge. The two meet at San Gabriel Reservoir and turn south, boring through the southern portion of the San Gabriels, emptying of the mountains near Azusa into the urban San Gabriel Valley, and eventually to thePeaks
Climate
The climate of the range varies with elevation from continental to Mediterranean, with mostly dry summers (except for scattered summer thunderstorms) and cold, wet winters. Snow can fall above elevation during cold fronts between November and April, but is most common in December through March. Annual precipitation totals are mostly in excess of on the coastal (southern) slopes above elevation, with up to falling in some areas above . The coastal (south) side of the range receives vastly more precipitation than the desert (northern) side. The highest precipitation is found in the central and eastern parts of the range (Mt. Wilson to Mt. San Antonio). Annual precipitation totals are highly variable from year to year, and can be extremely high during wet El Nino years (sometimes over , with single storm totals over ). Runoff from the mountains during big storms often produces flooding in adjacent foothill communities (especially in areas denuded by wildfires). The range is mostly smog-free above elevation, above the inversion layer. The large telescope installation at Mt. Wilson is a testimony to the clear atmospheric conditions that prevail, although light pollution from the L.A. basin below has hindered telescope activities in recent decades.Wildfires
The San Gabriel Mountains see wildfires frequently. The fires are often driven by dry Santa Ana wind events in the summer and fall. Notable wildfires in the San Gabriel Mountains have included the 2009 Station Fire, 2020 Bobcat Fire, the 2024 Bridge Fire, and the 2025 Greater Los Angeles Wildfires.Geology
Granitic and metasedimentary rocks are the primary constituent of the San Gabriel Mountains. Metasedimentary rocks were attached to the North American craton in the Precambrian eon, and granitic rocks formed throughout the Mesozoic as oceanic plates subducted underneath the North American west coast. Like nearly all of the other mountains in the Transverse Ranges, the San Gabriels are a series ofEcology
There are both areas of conifer as well as broadleaf forestation, including the presence of some endemic taxa. Conifer (pine, fir, cedar) and oak forests are most widespread above where the precipitation is above (the central and eastern high San Gabriels). In the wetter areas, madrone and bay laurel trees also occur in places, and ferns are common. Trees like willow, alder, and cottonwood are also found throughout the range along with the stream courses (riparian habitat), even at lower elevations. Chaparral (dense shrub, brush, and small tree) vegetation is widespread where there is no continuous tall tree cover, especially at lower elevations. Chaparral is highly adapted to fire and replaces trees for decades after fires. With the recent increase in wildfire frequency and damage, chaparral occupies more and more of the San Gabriels each year. There is a subspecies of the Leather Oak which is found only within the San Gabriel Mountains. The Rift Zone along the San Andreas Fault produces numerous springs, sag ponds, and wetland areas that are critical habitats for a variety of native species. A prime example of such a sag pond is Jackson Lake just west of Wrightwood. Larger animals include California mule deer, California black bear, San Pedro Martir coyote and the rarely seen mountain lion or cougar. Smaller mammals include raccoons, opossum, skunk, and bobcats. Golden and bald eagles are found rarely, but hawks are common. Rattlesnakes are common and often encountered on trails by hikers. Critically endangered yellow-legged frogs have declined or vanished from the streams due to the loss of suitable habitat. The San Gabriel Mountains were once home to a thriving population of Southern Steelhead. The Arroyo Seco and San Gabriel River had two major populations, but due to damming and channelization, these fish cannot make it upstream anymore. However, wild nativeTransportation
The main road that runs through the San Gabriel Mountains is the Angeles Crest Highway, State Route 2. It starts in the southwest at the city of La Cañada Flintridge and ends at its junction with State Route 138, just past Wrightwood, near the Victor Valley and the western Cajon Valley. Past its junction with Angeles Forest Highway, traveling east, Angeles Crest Highway features blind curves, various bumps, and potholes. This section of the "Crest" is closed during the winter due to rockfall and avalanche hazards. State Route 2, just past Mountain High, is called the Big Pines Highway to the Route 138 junction. Another key county route through, the mountains is Angeles Forest Highway. Angeles Forest Highway begins 11 miles northeast of La Cañada Flintridge at its Angeles Crest Highway junction. Ending near Acton, it allows easy access to the central Forest and the fast-growing Antelope Valley. Because the "Forest" and the "Crest" portion leading to La Cañada Flintridge is well traveled by Antelope Valley commuters, its road maintenance is much better, and it is open much of the winter. State Route 39 connected the city of Azusa with the Angeles Crest Highway until it was seriously damaged by landslides, first in 1978, and again in 2005. The highway was opened to emergency crews in February 2003. People heading to Mount Waterman must now travel west to Pasadena and then travel on the Angeles Crest Highway (Highway 2) in La Cañada Flintridge, a nearly two-hour trip. Reopening Highway 39 would cut the drive time to the Waterman Ski Area in half and shorten the trip east to Wrightwood. According to the Caltrans District Seven "Inside Seven" Newsletter, "Two projects that will address those issues and get the highway reopened are scheduled for construction soon. The first, building two retaining walls near the city of Azusa from Old San Gabriel Canyon Road to approximately south of SR-2, could begin in mid-2009. The second, a $45 million project to reconstruct the roadway, construct soldier pile retaining walls, repair drainage systems, install rockfall protection, and provide asphalt concrete overlay and traffic striping, should begin in fall 2010." In 2011, the planned repair of the road was abruptly terminated, due to concerns of high future maintenance costs, and potential impact on the local bighorn sheep population. However, in October 2016, Caltrans announced it was again considering plans to reopen the road, after pressure from local communities.Recreation
In the winter, snowboarding and skiing are quite popular in the San Gabriels, at Mountain High and Mt. Baldy. The two other resorts, Mount Waterman and Kratka Ridge, are rarely open due to insufficient snow. In the summer, canyoneering, hiking, backpacking, picnicking, and camping are some of the activities popular with visitors. From time to time, a hiker gets lost or stuck on a mountain ledge or may fall downhill. Some of the more extreme cases of emergency search-and-rescue efforts will often be given air time on Los Angeles television and radio newscasts. The Pacific Crest Trail passes along the mountain ridge. During the winter, many Southern California mountaineers climb a variety of snow routes and even some ice routes in the San Gabriel Mountains. Baldy Bowl is by far the most popular route, getting hundreds of climbers per season. There are many other routes, offering a variety of choices. Rock climbing is not as common in the San Gabriel Range as it is in neighboring areas, as this range is famous for loose rock. Various faults crisscross the range, making it one of the steepest and fastest-growing ranges in the world. Plate tectonic activity breaks up most rock, making it unsuitable for rock climbing. Williamson Rock was the most famous climbing area until it was closed to climbing. There are many other craggy areas scattered about the range that provide mostly traditional climbing opportunities. The Angeles National Forest Fire Lookout Association has rebuilt and operates Vetter Mountain Lookout, and Slide Mountain Lookout. The organization is rebuilding South Mount Hawkins Lookout.Nearby ranges
* San Rafael Hills *Gallery
References
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