At just over (or maybe under) 11,500 feet, San Gorgonio Mountain is Southern California's high point, considerably eclipsing rivals San Jacinto Peak and Mount San Antonio. This might just be the most inspiring summit view in SoCal, but you'll have to work for it. The shortest approach, via the Vivian Creek trail, is about 8 miles and 5.5K of vertical. The South Fork approach, from the north, chops a bit of vertical but adds a hefty mileage premium.
I particularly love the view of San Jacinto from atop San Gorgonio, with the dramatic plunge of Cochella Valley in between. Looking east you can see a sweeping view of Palm Springs and the Low Desert, with Arizona visible on a clear day beyond. To the north is Big Bear Lake and the High Desert. South is San Diego and the Inland Empire. And to west, you'll see Mount Baldy, the Santa Ana Mountains, the Pacific Ocean, and course the mighty Los Angeles Basin.