Cowabunga Kitesurfing near Piedras Blancas and San Simeon's Hearst Castle in San Luis Obispo County, California, an adventure traveler's choice.   Adventure Vacations continued   Adventure travelers are not limited to air and sea, and would indeed, be missing the majority of California’s natural geography should they ignore California’s Gold Country. Gold Cliff Mine in Angels Camp, for example, offers challenges with climbing, crawling and even diagonal hiking requiring knotted hand-lines on a 45 to 50-degree slope. While the payout doesn’t often come in large nuggets, the adventuresome spirit will discover another type of priceless experience as they explore an authentic gold mine’s deep passages and chambers.   In addition to the white water rafting we’ve found further north in Big Bar in Trinity County, whitewater rafting on the American River and the Sierra Nevada foothills near the historic  gold towns Auburn and Coloma, ranges from Class 3 to  5—the most challenging of rapids and kayaking, requiring knowledge and skill.   As long as you're in the mountains, why not tackle some serious challenges at Mammoth Lakes, where skiing, snowboarding, snowmobiling, ice fishing, and ice skating offer a few great winter adventures. When it's open, Lassen Volcanic National Park is also ideal for extreme thrills. You usually have to climb to get your boarding in, but the region is pristine... kept close to its natural state.   In the deserts of California, Joshua Tree National Park offers high desert rock climbing with crack, slab and steep-face climbing.  There are more than 400 formations and 8,000 climb routes for all levels, plus many climbing schools that rent equipment and shoes. Jeep tours offer all kinds of adventures and breath-taking vistas, and usually include information along the way. All you need for this type of excursion is some sturdy clothing, an adventuresome spirit, and joy riding.   For extreme bicycling, the Death Ride is one of the best tests of human strength. The roads are steep and require that you train (usually, anyway) before taking on the annual event's challenges. That event is held in Alpine County.