Organ Pipe Cactus National Monument is a biosphere reserve in the Sonoran Desert, set aside to protect species found nowhere else in the United States. The organ pipe cactus itself — a multi-armed columnar cactus that can grow to seven metres — reaches its northern limit here. Saguaro, cholla, palo verde and ironwood fill the landscape alongside it.
Inside the monument, visitors can explore a quality visitors centre, drive scenic dirt roads through cactus-studded valleys, day-hike the trails, or trek into the backcountry for overnight trips. The Ajo Mountain Drive is a 21-mile gravel loop through some of the most dramatic scenery.
The climate is typical Sonoran Desert: mild winters and brutally hot summers, when temperatures regularly exceed 40°C (104°F). Monsoonal thunderstorms arrive mid-July through mid-September. Winter and early spring are the best times to visit — wildflower blooms in March and April can be spectacular.
The monument lies on the Arizona–Mexico border, about three hours west of Tucson. To its northwest is the Cabeza Prieta National Wildlife Refuge; on the Mexican side, the Pinacate and Gran Desierto Biosphere Reserve. Together they form one of the largest protected desert areas in North America.
There is a campground within the park. Motels and RV parks can be found in the small towns of Ajo and Lukeville (also known as Gringo Pass) to the north and south.