Mount San Antonio

California Class 2 San Gabriel Mountains

Rank 21

Elevation landscape

10,064 ft

Prominence height

6,247 ft

Difficulty signal_cellular_alt

Class 2

Est. Time schedule

6–10 hr

Distance route

10–11 mi

Vert Gain trending_up

3,900–4,300 ft

Mount San Antonio ranks No. 21 among the 57 ultra-prominent peaks in the contiguous United States, rising 10,064 feet in the San Gabriel Mountains of Southern California, with 6,247 feet of clean prominence. It is the highest summit in the San Gabriel Mountains and the high point of Los Angeles County on the Los Angeles–San Bernardino county boundary. Most hikers use the Devil's Backbone from Manker Flats for roughly 10 to 11 miles round-trip with about 3,900 to 4,300 feet of gain on Class 1–2 terrain with sustained ridge exposure. Parking at Manker Flats requires a day-use fee or valid federal recreation pass.

More commonly called Mount Baldy, the peak is visible across much of the Los Angeles Basin, where its snow-capped profile appears above the horizon on clear winter and spring mornings. The summit lies roughly 35 miles northeast of downtown Los Angeles within Angeles National Forest.

The San Gabriels are a tectonically active range uplifting rapidly along the San Andreas and related fault systems. Baldy's upper slopes are composed of granitic rock characteristic of the Transverse Ranges. The Devil's Backbone, which forms the final section of the standard route, is a narrow crest shaped by frost action and mass wasting, with steep drops on both sides. The Sierra Club Ski Hut at approximately 8,200 feet on the Baldy Bowl approach has served climbers and skiers for decades and is reservable through the Sierra Club Angeles Chapter.

Recommended Route

Devil's Backbone from Manker Flats

The standard route begins at Manker Flats Trailhead at approximately 6,160 feet and follows the road or trail up to Baldy Notch before continuing along the Devil's Backbone ridge to the summit. From Manker Flats, the full outing commonly runs 10 to 11 miles round-trip with roughly 3,900 to 4,300 feet of gain; parties using the Mount Baldy Resort ski lift to Baldy Notch substantially reduce both. From the notch at approximately 7,800 feet, the Backbone Trail traverses a narrow exposed crest northeast toward the summit, with steep drops on both sides in sections. In dry conditions the ridge is Class 1–2 hiking with exposure; wind, snow, or ice can make the terrain significantly more serious. Most parties allow 6 to 10 hours round-trip from Manker Flats.

Other established routes include the Baldy Bowl Trail from Manker Flats via the Sierra Club Ski Hut, a steeper alternative with a sustained scree section, and the longer Icehouse Canyon approach from the east.

Key Landmarks

Manker Flats Trailhead (~6,160 ft)
Baldy Notch (~7,800 ft)
Devil's Backbone Ridge
Summit (10,064 ft)

warning

Afternoon thunderstorms develop rapidly over the summit July through August. The exposed Backbone ridge offers no shelter; parties should plan to be off the ridge by midday during monsoon season.

Permits & Camping

Climbing Permits

Parking at Manker Flats requires payment of a day-use fee or a valid federal recreation pass; the Adventure Pass has historically been the applicable instrument for this area, but the Manker Flat day-use fee and pass rules are subject to change. Day-hiking the Devil's Backbone route generally does not require a wilderness permit, but wilderness permits are required for entry into designated wilderness areas along the route and are free. Confirm current parking, pass, and permit requirements directly with Angeles National Forest before departure.

Camping & Wilderness

Backcountry camping rules vary by wilderness area and management unit around Mount Baldy; check current Angeles National Forest and San Bernardino National Forest guidance before planning an overnight trip. A California campfire permit may be required for stoves or open flames outside developed facilities, and seasonal fire restrictions frequently prohibit all flames. The Sierra Club Ski Hut at 8,200 feet is reservable through the Sierra Club Angeles Chapter and provides a shelter option for parties making an early start. Water may be available near Manker Flats or developed facilities; do not rely on untreated backcountry sources.

Summit N 34.28940° W 117.64640°. Manker Flats Trailhead: N 34.23320° W 117.64660° (~6,160 ft). Elevation 10,064 ft; prominence 6,247 ft. Angeles National Forest, San Gabriel Mountains.

Wildlife & Seasonal Conditions

Comfort on exposed Class 2 ridge terrain is required in dry summer conditions. Snow or ice above Baldy Notch requires self-arrest competency with ice axe and crampons, and winter and spring conditions can persist on the upper route well into May. Rockfall from parties above in Baldy Bowl is a hazard on that approach; the Devil's Backbone route reduces this exposure. The exposed summit ridge carries serious consequence in wind or icy conditions. Trailhead parking at Manker Flats fills by early morning on peak-season weekends.