California's largest state park is hot, almost shadeless, and waterless for the entire leg of the PCT that traverses the San Felipe Hills. But if you can handle the difficulties--an enormous load of water--the desert will reward your pack-mule toughness. The open terrain offers constantly changing views of the myriad ridges and gullies defining these hills. Beyond the sprawling, 600,000-acre park, you'll see San Ysidro Mountain across the Montezuma Valley, and the higher, tantalizingly green Volcan Mountains. Look for elusive bighorn sheep, and be ready to encounter barrel cactus, agave, cholla, sparse scrub oak, juniper, dense chaparral, and "forests" of ocotillo shrubs, which grow in single stalks 10 to 15 feet tall and bloom in spring with flaming-red flowers. At elevations from 2,200 to 4,400 feet, this hike is best done from fall through early spring. Start the hot ascent of Grapevine Mountain at dawn. Wildflowers bloom from January through March.