The 70,000-square-mile Sky Island region of southeastern Arizona, southwestern New Mexico, and northwestern Mexico contains 40 mountain ranges that are connected by the corridors they create for the movement of animals.  Each Sky Island has a distinct ecosystem, and the region is globally unique because of its rich diversity of species and habitats.  The Rincon Mountain District of Saguaro National Park is included in this "Sky Island Archipelago" -- containing the largest roadless (wilderness) Sky Island in North America.

Before the climate in the southwest began to change some 15,000 years ago, forests stretched from the Rockies down into the Mexican Sierra Madres.  Wolves, black bears, and jaguars moved freely along this wooded corridor.  But with the end of the ice age, temperatures rose and precipitation dropped, and the desert to the south spread north.  The species that needed water and cooler temperatures (like squirrels and fish) found themselves marooned at high elevations by widening arid gulfs between themselves and other animal life.  The result were these mountaintop "Sky Islands" amid a 20-million-acre sea of desert -- described by University of Arizona botanist Peter Warshall as ecosystems "unique on the planet."