The park is divided into two sections, called districts, lying approximately 20 miles east and 15 miles west of the center of the city of Tucson, Arizona.
There is a visitor center in each of the two districts. Both are easily reached by car from Tucson, but there is no public transport into the park. Both districts conserve fine tracts of the Sonoran Desert, including ranges of significant hills, the Tucson Mountains in the west and the Rincon Mountains in the east.
The park gets its name from the saguaro, a large cactus which is native to the region. Many other kinds of cactus, including barrel, cholla, and prickly pear, are abundant in the park. One endangered animal, the Lesser Long-nosed Bat, lives in the park part of the year during its migration, together with one threatened species, the Mexican Spotted Owl.
The Rincon Mountain District is located at the eastern edge of Tucson, and includes the land protected in the original National Monument. Plant communities at the lower elevations in the park are typical of the Sonoran Desert, while the Rincon Mountains support a temperate coniferous forest.
The highest peak in this range is Mica Mountain, at an elevation of 8,664 feet (2,641 m). This side of the park has fewer saguaro than its western counterpart, but they are larger in size due to higher amounts of rainfall and runoff from the Rincon Mountains.