Organ Pipe Cactus National Monument is situated in the deep south of Arizona near the Mexico-United States border. The International Biosphere Reserve is named after the Organ Pipe Cactus (Stenocereus thurberi). It is the only place in the United States where Organ Pipe Cactuses grow wild (see Wikipedia). Along with the Organ Pipe Cactus, many other cacti species and other desert flora native to the Yuma Desert section of the Sonoran Desert region grow in the National Monument, for example the Sanita cactus (Lophocereus schottii). The area is also home to many desert animals.

Organ Pipe Cactuses have several narrow stems that rise vertically, growing from a single short trunk just above the ground level. These stems are about 6 inches (15 cm) thick and grow to a height of about 16 feet (about 5 m) and more.

The Organ Pipe Cactus National Monument is a desert area next to the Ajo Range, a high, rocky ridge which forms the eastern boundary of the preserve. It's not only a place to see desert plants and wildlife but also an interesting geological area. The Ajo Mountains mainly consist of colored volcanic rock.

I recommed to do the 21 mile Ajo Mountain Drive and hike the Bull Pasture/Estes Canyon trail. The 3.5 mile loop is probably the most interesting of only a few maintained paths in the Organ Pipe National Monument. Be sure to bring enough water with you!

The best time to visit the Organ Pipe National Monument is probably spring. Summer's often too hot for hiking (and camping as well). The National Park Service offers lots of information to plan a visit. I also recommend the American Southwest Website.