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. The total area in 2011 was 91,442 acres of which 70,905 acres is designated wilderness. 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.

Below: Prickly pears typically grow with flat, rounded cladodes (also called platyclades) that are armed with two kinds of spines; large, smooth, fixed spines and small, hairlike prickles called glochids, that easily penetrate skin and detach from the plant. Many types of prickly pears grow into dense, tangled structures. Below are three photos of prickly pear with pink fruit and three photos of prickly pear with dark red fruit.

The fruit of prickly pears, commonly called cactus fruit, cactus fig, Indian fig or tuna in Spanish, is edible, although it has to be peeled carefully to remove the small spines on the outer skin before consumption. If the outer layer is not properly removed, glochids can be ingested, causing discomfort of the throat, lips, and tongue, as the small spines are easily lodged in the skin. Native Americans, like the Tequesta, would roll the fruit around in a suitable medium to "sand" off the glochids. Alternatively, rotating the fruit in the flame of a campfire or torch has been used to remove the glochids. Today, parthenocarpic (seedless) cultivars are also available. The two RV Gypsies do NOT recommend for anyone to try to do this.