The highest point in L.A. County is Mt. Baldy (officially known as Mt. San Antonio). The most serious trail up the summit is the so-called Ski Hut Trail from Manker Flats. You start at approximately 6,000 feet and gain 3,900 vertical feet in the next 4.2 miles. This calculates to a mind-blowing 928 feet of elevation gain per mile. To put this in perspective, when you hike Mt. Whitney (tallest peak in the Lower 48), while you go much farther and higher, your elevation gain is only 563 feet per mile. In other words, this is a kickass hike, and almost all uphill! Summer or winter, sun or snow, this is a strenuous little 8.4-mile day hike. My daughter and I have even come up with some colorful nicknames for some segments like Death Hill, the Hill of Death, Death Creek ... you get the idea. Enjoy! Baldy Road to Manker Flats: The trail head starts by the Port A Pottys on your left. Don't forget a wilderness pass to park your car: $5 for a day pass, or $30 for an annual pass; available at the information center in Baldy Village or at Big 5 and REI stores.