Highway 38 to Valley of the Falls, ending at the Vivian Creek Trailhead at ~6,000ft elev., about halfway to the proper summit of Mt. San Gorgonio. The stretch that is Valley of the Falls is pretty gnarly-- it picks up about 1,500ft in just under 4 miles, and there's a stretch of half a mile or so of +10%. Two and a half hours to get up there, less than 40 minutes to get back down.