San Gabriel Mountains - Geography

Geography

The highest elevation, Mount San Antonio at 10,064 ft., rises towards the eastern extremity of the range which extends from the Cajon Pass (Interstate 15 Freeway) on the east, where the San Gabriel Mountain Range meets the San Bernardino Mountain Range, westward to meet the Santa Monica and Santa Susanna ranges at approximately Tejon Pass (Interstate 5 Freeway).

The Range is bound on the north by the Antelope Valley and the Mojave Desert and to the south by the communities of greater Los Angeles area. In the western portion of the San Gabriel Mountain Range, the Sierra Pelona Ridge stretches from approximately Soledad Canyon (14 Freeway and railroad right-of-way), formed by the Santa Clara River. The Sierra Pelona Ridge includes Liebre Mountain, Sawmill Mountain, Grass Mountain, Redrock Peak, Burnt Peak, most of which is part of the Angeles National Forest, but also features several rural communities.

North of San Fernando, the San Gabriel Mountains crest abruptly up to almost 4,000 feet (1,200 m). 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 is Mount Gleason, which at 6,502 feet (1,982 m), is the highest in this region of the San Gabriels. South of the gorge are the southern "foothills" of the mountains, which rise abruptly 4,000 feet (1,200 m) 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 5,710 feet (1,740 m). 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 30 miles (48 km) in length that includes most of the highest peaks in the range: Waterman Mountain, at 8,038 feet (2,450 m); Mount Islip, at 8,250 feet (2,510 m), Mount Baden-Powell, at 9,399 feet (2,865 m), Pine Mountain, at 9,648 feet (2,941 m), and finally Mount San Antonio, the highest peak in the range at 10,068 feet (3,069 m).

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 14 miles (23 km) eastward, and the East Fork, starting north of Mount San Antonio, flows 18 miles (29 km) 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 out of the mountains near Azusa into the urban San Gabriel Valley, and eventually to the Pacific Ocean near Seal Beach.

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. Little Rock, 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 Inland Empire cities of Claremont, Upland and Rancho Cucamonga. However, there are still several notable peaks in this region, including Telegraph Peak, at 8,985 feet (2,739 m), Cucamonga Peak, at 8,859 feet (2,700 m), and Ontario Peak, rising 8,693 feet (2,650 m). Lytle Creek, flowing generally southwest, 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.