At 11,499 feet, San Gorgonio Mountain is the highest peak in Southern California. I've got my boots on!
Here's a map showing the proximity of San Gorgonio Mountain to Yucaipa. According to Google Earth, the summit is just 13 miles from my front door!* The trail to the summit is 17.5 miles round trip, with a 5,420-foot gain, and is rated "Class 1, strenuous". Fun fun fun fun!