The hook
The highest mountain in Southern California isn't in the Sierra. It's Old Greyback, an 11,503-foot dome above the Inland Empire, high enough that its summit clears the treeline entirely.
01Why it's worth it
San Gorgonio, called Old Greyback for the pale rock along its summit ridge, tops out at 11,503 feet, higher than any point in Southern California or anywhere in the Transverse Ranges. It rises past the tree line, the only SoCal peak that does, so the last stretch to the top crosses open alpine rock with nothing but sky above it. The view from up there is hard to believe. The summit is visible from Mount Whitney 190 miles away, one of the longest sightlines in the country, and on a clear day you can pick out the ocean, the Mojave, and the Sierra on the same horizon. Getting there is the price. Every route is long, the shortest around seventeen miles round trip with close to 5,500 feet of climbing, and the whole massif sits inside the San Gorgonio Wilderness, which caps how many people enter each day. Most hikers do it as a very long single push or split it over a night at one of the trail camps.
02How to experience it
The main trailheads are Vivian Creek and South Fork, off Highway 38 past Redlands, about eight hours from the Bay. You need a wilderness permit, free but quota-limited, from the San Bernardino National Forest, and you want the window from roughly June through October unless you're equipped for snow and ice. Start before dawn. Carry far more water than seems reasonable and real layers for the summit, which stays cold and windy even in July. This is a serious mountain day, not a casual hike.