Saguaro National Park

The nation's largest cacti grow only in the Sonoran Desert, and this park protects them on 92,000 acres split across two districts flanking Tucson. The Tucson Mountain District to the west holds denser stands of saguaro; the Rincon Mountain District to the east climbs higher into sky-island terrain where pine forest replaces cactus above 8,000 feet. Both districts conserve what the Hohokam knew between 200 and 1450 — that the Santa Cruz River valley, though mostly dry now, sustains life in forms found nowhere else. A saguaro grows an inch a year and may live two centuries; the first arm appears around age seventy. The park estimates 1.8 million of them stand here, some weighing two tons when rain-swollen, their wooden ribs wrapped in green flesh that stores summer monsoon water through the lean months. President Hoover established the original monument in the Rincons in 1933; Kennedy added the Tucson Mountains in 1961; Congress combined them into a national park in 1994.