Difficulty: Class I to III

Season: All year, best in winter

Trip Length: One to seven days

The three river canyons of Big Bend National Park—Santa Elena, Mariscal, and Boquillas—can be rafted either singly or all together as a seven-day trip. Each canyon has a distinctive character, so picking out just one to do is thornier than canyon-bottom cactus. The Santa Elena is the first and most popular canyon. Its charms include waterfalls, fossils, petroglyphs, wildlife, and the notorious Rock Slide Rapids—a walloping stretch of hard-to-figure whitewater. Boquillas Canyon is much calmer: Its whitewater is barely Class II. The 4,000-foot canyon walls, caves and rock formations make this a good trip for sinking into geological time—slow and majestic. Mariscal is a festive canyon, with lower walls and lively rapids. It is the most remote of Big Bend's canyons: beckoning those who seek wilderness.