Mt. San Antonio

Mt. San Antonio (Baldy) - from the south-eastern slope, looking north-west to the peak - photo Eric T. Gunther

This file is licensed under the Creative Commons Attribution 3.0 Unported licence. 

Mount San Antonio (Baldy)

3069m, P1917m

Location

California, USA

Coordinates

34.2892° N, -117.6464° E

Range

San Gabriel Mountains, Transverse Ranges 

Description of the mountain and geology

Mount San Antonio—widely known as Mount Baldy— lies on the border of Los Angeles and San Bernardino counties in southern California. Indigenous names historically used by local First Peoples include Yoát (Tongva/Gabrielino), Jukuma’nga (Serrano), and Joat (Tataviam).

Mount San Antonio is the culminating summit of the San Gabriel block, a rugged, rising massif shaped by the ongoing tectonic compression between the Pacific and North American plates. Its core geology consists of Pre-cambrian gneiss and schist, intruded by later granitic plutons, with extensive faulting related to the nearby San Andreas Fault system.

The mountain’s steep south face drops sharply toward Los Angeles, while its broad northern slopes face the Mojave Desert. A classic alpine environment exists at higher elevation, with sub-alpine forest transitioning to open, windswept slopes near the summit. Active uplift, rockfall, and seasonal snow erosion continue to sculpt its topography.

Archaeological, Historical and Cultural Notes

For thousands of years, Mount San Antonio stood at the meeting point of several indigenous groups, including the Tongva, Serrano, and Tataviam peoples, functioning as a landmark, seasonal hunting area, and place of spiritual significance. With Spanish colonial expansion in the 18th century, the mountain acquired the name San Antonio after Saint Anthony of Padua. In the American frontier period of the 19th century, its bald upper slopes earned the English nickname “Mount Baldy,” which remains the most widely used name today. By the early 20th century, the peak became central to the recreational history of southern California, with the establishment of the Mount Baldy Trail, early mountain lodges, and one of the region’s first organised ski areas.

Summit Description

The summit is a broad, gently domed plateau, largely free of vegetation and marked by exposed rock, gravel, and wind-shaped features typical of high ridgelines in sub-tropical climates. A metal plaque marks the high point, and panoramic views extend across the entire Los Angeles Basin to the Pacific Ocean, as well as northward across the Mojave Desert. To the west, the ridge continues to West Baldy 3049m, P42m, and to the south, the precipitous Bowl face drops sharply toward the San Antonio Canyon.

Popular Routes to the Summit

Two primary routes are established:

- Baldy Bowl–Ski Hut Trail: Beginning at Manker Flats, the trail climbs steeply past the San Antonio Falls to the historic Sierra Club Ski Hut, then ascends the Baldy Bowl via sustained gradients to reach the summit ridge. This is the classic, direct ascent.

- Devil’s Backbone Trail: Also starting at Manker Flats, this route ascends via Baldy Notch and follows the narrow, scenic Devil’s Backbone ridge, offering airy traverses and dramatic views before reaching the upper slopes. This route can be treacherous in winter due to icy snow and very strong, cold winds.

Other items of interest

Mount San Antonio serves as a major recreational centre for southern California, offering year-round hiking, backcountry skiing, and alpine training opportunities. Its proximity to Los Angeles makes it one of the most climbed high peaks in the United States. Despite its accessibility, rapidly changing weather, wild fires (with consequential trail closures), winter ice, and steep slopes result in regular rescues, and the mountain is considered serious terrain in adverse conditions. 

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