Saguaro cacti are the quintessential symbol of the American desert and occur naturally only here in the Sonoran Desert. Sensitive to fire and frost, and exceedingly slow to mature, these massive, treelike cacti grow in great profusion around Tucson but have long been threatened by both development and plant collectors. In 1933, to protect these desert giants, the federal government set aside two large tracts of land as a saguaro preserve. This preserve eventually became Saguaro National Park. The two units of the park, one on the east side of the city (Rincon Mountain District) and one on the west (Tucson Mountain District), preserve not only dense stands of saguaros, but also the many other wild inhabitants of this part of the Sonoran Desert. Both units have loop roads, nature trails, hiking trails, and picnic grounds.
The west unit of the park, because of its proximity to both the Arizona-Sonora Desert Museum and Old Tucson Studios, is the more popular area to visit (and your best choice if you're trying to do a lot in a short amount of time). This also happens to be where you'll see the most impressive stands of saguaros. Be sure to take the scenic Bajada Loop Drive, where you'll find good views and several hiking trails (the Hugh Morris Trail involves a long, steep climb, but great views are the reward). To reach the west unit of the park, follow Speedway Boulevard west from downtown Tucson (it becomes Gates Pass Blvd.).
The east section of the park contains an older area of saguaro "forest" at the foot of the Rincon Mountains. This section is popular with hikers because most of it has no roads. It has a visitor center, a loop scenic drive, a picnic area, and a trail open to mountain bikes (the paved loop drive is a great road-bike ride). To reach the east unit of the park, take Speedway Boulevard east, then head south on Freeman Road to Old Spanish Trail.
Sunset on Signal Hill -- A hike to Signal Hill, located off the Bajada Loop Drive in Saguaro National Park's west unit and only a quarter-mile walk from the parking area, will reward you with not only a grand sunset vista away from the crowds at Gates Pass, but also the sight of dozens of petroglyphs.