The Saguaro Desert is enclosed within the Saguaro National Park and is comprised of two separate units. The Tucson district (TD) 16 km (10 miles) west of Tucson, in Pima county in southeastern Arizona and the Rincon district (RD) about 16 km (10 miles) east of the same city. These two units preserve Sonoran Desert landscapes, fauna, and flora, particularly the saguaro cactus.

The volcanic rocks on the surface of the TD differ greatly from the surface rocks of the RD. Crustal stretching displaced rocks for over the past 30 million years and in doing so, move the rock from beneath the Tucson Mountains of the TD to form the Rincon Mountains of the RD. The uplifted, domed, and eroded rock of the Rincon Mountains are significantly higher and wetter than the Tucson Mountains. The Rincon Mountain are one of the Madrean Sky Islands between the southern Rocky Mountains and the Sierra Madre Oriental in Mexico and they support high biodiversity, being home to many plants and animals that do not live in the Tuscon Mountians.

Early wayfarers include the Hohokam, Sobaipuri, Tohono O′odham, Apaches, Spanish Explorers, missionaries, miners, homesteaders, and ranchers.