Organ Pipe Cactus National Monument is a showcase biosphere -wilderness preserve for the flora and fauna of the Sonoran Desert region within Southern Arizona. The namesake species of Organ Pipe Cactus National Monument is the organ pipe cactus (Stenocereus thurberi). With many slender, curving stems that some believe resemble the pipes of an old-fashioned organ. They are the second-largest columnar cactus in the United States and can grow up to 23 feet tall. They are second only to saguaro cactus (that also grow in abundance in the park) that can grow 40 to 60 feet tall.
The landscape is also showcase for the geologic and tectonic features of the Basin & Range Physiographic Province. The park's mountainous areas provide exposures of Cenozoic-age volcanic rocks (lava flows and tephra deposits of rhyolite, andesite, and basalt composition). These rocks rest unconformable on faulted metamorphic and ignous rocks basement rocks of Precambrian age.
This collection of images includes pictures mostly taken along the Ajo Mountain Drive, a mosly unpaved but maintained one-way loop road that traverses the pediments and foothills below the higher peaks of the Ajo Range to the lowlands of the alluvium-filled Sonoyta Valley. Learn more about the park's amazing geology from the NPS report below.
Organ Pipe Cactus National Monument Geologic Resources Inventory Report: U.S. National Park Service Natural Resource Report NPS/NRSS/GRD/NRR—2022/2399, 102 p. (.pdf file).
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Fig. 1 - NPS map of Organ Pipe Cactus National Monument.
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