Sky Islands: Mountains That Float Above the Desert

Southeast Arizona holds one of the most biologically extraordinary landscapes in North America, and almost nobody outside the birding community knows it exists. The mountain ranges here, the Chiricahuas, the Huachucas, the Santa Ritas, the Pinaleños, rise from Sonoran Desert floor at roughly three thousand feet to alpine meadow at nine thousand feet or higher. Each range is a biological island, isolated from its neighbors by desert valleys, accumulating its own assemblage of species over thousands of years of geographic separation.

Scientists call this the Madrean Archipelago, a chain of sky islands connecting the Sonoran Desert ecosystem with the Sierra Madre of Mexico. Coronado National Forest, which administers these ranges as a scattered mosaic of units across southeastern Arizona and a sliver of New Mexico, contains more species of birds than any other national forest in the United States. More than three hundred species have been recorded in the Huachuca Mountains alone. Rare species that breed only in Mexico extend their range into these mountains because the habitat connects across the international border.

The ecological richness is a product of geography. Cold air pooling in the canyons creates riparian microhabitats at desert elevation. The altitudinal gradient from desert floor to spruce-fir canopy compresses what would elsewhere be hundreds of miles of latitudinal variation into a single mountain range you can drive across in an afternoon.

Coronado National Forest takes its name from the Spanish explorer Francisco Vásquez de Coronado, who crossed these ranges in fifteen forty in search of the mythical Seven Cities of Gold and found instead the Pueblo towns of the Zuni. He returned to New Spain having covered thousands of miles and found nothing he was looking for. The landscape he crossed is now a national forest named in his honor.