The San Gabriel Mountains () are a mountain range located in Los Angeles and San Bernardino counties, California, United States. The mountain range is part of the Transverse Ranges and lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east. The range lies in, and is surrounded by, the Angeles and San Bernardino National Forests, with the San Andreas Fault as its northern border.
The highest peak in the range is Mount San Antonio, commonly referred to as Mt. Baldy. Mount Wilson is another notable peak, known for the Mount Wilson Observatory and the antenna farm that houses many of the transmitters for local media. The observatory may be visited by the public. On October 10, 2014, President Barack Obama designated the area the San Gabriel Mountains National Monument. The Trust for Public Land has protected more than of land in the San Gabriel Mountains, its foothills, and the Angeles National Forest. The mountains were once known as the Sierra Madre, lending the name to the city of Sierra Madre; however, since 1965, the name "Sierra Madre" has referred to a different mountain range to the west in Santa Barbara County.
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 the Miocene and has since been dissected by numerous rivers and washes.
Setting 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 the Los Angeles River.
Southeast of Big Tujunga Canyon, the southern front range of the San Gabriels gradually grows in elevation, culminating in notable peaks such as Mount Wilson at . On the north the range is abruptly dissected by the canyon of the West Fork San Gabriel River. Even further north the range slopes up into the towering main crest of the San Gabriels, a sweeping arc-shaped massif in length that includes most of the highest peaks in the range: Waterman Mountain, at ; Mount Islip, at , Mount Baden-Powell, at , Pine Mountain, at , and Mount San Antonio, the highest peak in the range at .
On the north slopes of the San Gabriel crest, the northern ranks of mountains drop down incrementally to the floor of the Mojave Desert in a much more gradual manner than the sheer southern flank. The Angeles Crest Highway, one of the main routes across the San Gabriels, runs through this area from west to east. Littlerock, Big Rock, and Sheep Creeks drain off the northern part of the mountains, forming large alluvial fans as they descend into the Mojave. To the east, the San Andreas Fault cuts across the range, forming a series of long, straight, and narrow depressions, including Swarthout Valley and Lone Pine Canyon. South of Mount San Antonio, San Antonio Creek drains the mountains, cutting the deep San Antonio Canyon.
East of San Antonio Canyon, the range gradually loses elevation, and the highest peaks in this section of the mountain range are in the south, rising dramatically above the cities of Claremont, Upland and Rancho Cucamonga. However, there are still several notable peaks in this region, including Telegraph Peak, at , Cucamonga Peak, at , and Ontario Peak, rising . Lytle Creek, flowing generally southeast, drains most of the extreme eastern San Gabriels. The range terminates at Cajon Pass, through which runs Interstate 15, and beyond which rise the even higher San Bernardino Mountains.
Locale 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 the Los Angeles city communities of Sylmar, Pacoima, and Sunland-Tujunga, as well as cities and unincorporated areas of San Fernando, La Crescenta, La Cañada Flintridge, Altadena, Pasadena, Sierra Madre, Arcadia, Monrovia, Bradbury, Duarte, Azusa, Glendora, San Dimas, La Verne, Claremont, Upland, Rancho Cucamonga, Fontana, Rialto and West San Bernardino. The north side of the range is less densely populated and includes the city of Palmdale as well as the small unincorporated towns of Acton, Littlerock, Pearblossom, Valyermo, Llano, Piñon Hills, and Phelan. At the west end of the range lies the city of Santa Clarita. Within the mountains themselves are the small unincorporated communities of Mount Baldy, Wrightwood, Big Pines and Lytle Creek.
Hydrology 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, draining the mountains near Azusa, flowing into the urban San Gabriel Valley, and eventually to the Pacific Ocean near Seal Beach.
Peaks
San Gabriel Mountains peaks within the Angeles National Forest include: Mount San Antonio (Mount Baldy), Pine Mountain, Dawson Peak, Mount Harwood, Mount Baden-Powell, Throop Peak, Mount Burnham, Telegraph Peak, Cucamonga Peak, Ontario Peak, Mount Lewis, Timber Mountain, Mount Islip, — site of historic Mt. Islip fire lookout tower USFS.gov: Mt. Islip fire lookout tower Mount Williamson, Waterman Mountain, Iron Mountain, South Mount Hawkins, — lookout destroyed in Curve Fire, 2002 Pallett Mountain, Pacifico Mountain, Mount Gleason, Strawberry Peak, San Gabriel Peak, Mount Disappointment, Mount Lawlor, Vetter Mountain, — site of historic Vetter Mountain Fire lookout tower Rattlesnake Peak, Mount Wilson, — location of the Mount Wilson Observatory Mount Lowe, — site of Mount Lowe Railway Iron Mountain, Josephine Peak, Condor Peak, Monrovia Peak, Rankin Peak, Smith Mountain, Mount Lukens, Mount McKinley, Magic Mountain, Mendenhall Peak, Clamshell Peak, Los Piñetos Peak Kagel Mountain, Potato Mountain, Echo Mountain, Bare Mountain 6,388 ft (1,947 m) Hoyt Mountain 4,416 ft (1,346 m) Wright Mountain 8,505 ft (2,592 m) Mount Markham 5,742 ft (1,750 m) Akawie Peak 7,283 ft (2,220 m)
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 sees frequent wildfires. They 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 during the Precambrian era, 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 of fault blocks that were uplifted in the Cenozoic. Tectonic uplift rates and erosion rates systematically increase as topography steepens eastward in the San Gabriel Mountains, where the San Andreas and San Jacinto faults meet.
Current rates of erosion in the eastern San Gabriel mountains are among the fastest in the continental United States and have accelerated in response to the increased frequency of wildfires over the 1900s. Over future centuries, it remains unclear whether soil and brush ecosystems in the San Gabriel mountains will continue to re-establish soil and vegetation after increasing fire and soil-erosion frequencies, or if increasing fire frequencies and erosion will strip soils and permanently alter soil cover and vegetation types across the mountain ecosystem.
History Indigenous History For thousands of years before the arrival of the Spanish in the Los Angeles basin, the San Gabriel Mountains have been home to Indigenous peoples. Several of the groups that either inhabited or traveled through the mountain range include the Gabrielino-Tongva, Fernandeño Tataviam, Serrano (Yuhaviatam), Kitanemuk, and Chumash. These groups relied on the San Gabriel Mountains for resources and took care to sustain its ecosystem. The Tongva, for instance, practiced sustainable resource management. Women were practitioners of ethnobotany and gathered food from plants such as acorns (kwi), chia seeds, manzanita berries, and mountain cherries. Men hunted deer and rabbits using greasewood-shaft arrows, while the community’s fishermen caught steelhead trout with yucca-fiber nets. Controlled fires were also used deliberately to promote growth.
In addition to being a massive resource base, the mountains served the people as a sacred and cultural landscape and were viewed as living entities The legend of Mount San Antonio’s (Mount Baldy) creation describes two brothers, Sea-god and Land-god, who fought over humanity. When Sea-god tried to flood the earth, Land-god raised the mountains to protect the people, forming the San Gabriel range. Another myth goes that the Serrano followed a white eagle to settle around Mount San Antonio, which marked a territorial boundary between their people and the Tongva.