Organ Pipe Cactus National Monument

This UNESCO biosphere reserve on the Arizona-Mexico border is the only place in the United States where organ pipe cactus grows wild, alongside senita, saguaro, and the rest of the Sonoran Desert's rich plant life. About 95 percent of the monument is designated wilderness, crossed by scenic drives like the Ajo Mountain loop.

Spot cacti and desert wildlife on short nature trails and drive the Ajo Mountain loop; young kids can earn a Junior Ranger badge. For a challenge, hike the rugged Bull Pasture and Estes Canyon loop into the Ajo Mountains.