Saguaro National Park is an American national park in Pima County, southeastern Arizona. The 92,000-acre (37,000 ha) park consists of two separate areas—the Tucson Mountain District (TMD) about 10 miles (16 km) west of the city of Tucson and the Rincon Mountain District (RMD) about 10 miles (16 km) east of the city—that preserve Sonoran Desert landscapes, fauna, and flora, including the giant saguaro cactus.
The volcanic rocks on the surface of the Tucson Mountain District differ greatly from the surface rocks of the Rincon Mountain District; over the past 30 million years, crustal stretching displaced rocks from beneath the Tucson Mountains of the Tucson Mountain District to form the Rincon Mountains of the Rincon Mountain District. Uplifted, domed, and eroded, the Rincon Mountains are significantly higher and wetter than the Tucson Mountains. The Rincons, as one of the Madrean Sky Islands between the southern Rocky Mountains and the Sierra Madre Oriental in Mexico, support high biodiversity and are home to many plants and animals that do not live in the Tucson Mountain District.