In the southwestern United States and northwestern Mexico lies a region boasting the highest biodiversity in inland North America. Isolated mountain ranges topped by 10,000-foot peaks rise from intervening desert valleys and grasslands, prompting the nickname “Sky Islands.” A unique array of geographic, topographic and climatic influences create a bewildering variety of plants and animals here, many imperiled or found nowhere else.

Also called the Madrean Archipelago, dozens of distinct mountain ranges scattered on both sides of the U.S.-Mexico border function as high-country stepping stones between the subtropical Sierra Madre to the south and the temperate Rocky Mountains to the north. The area also lies along the confluence of the Sonoran and Chihuahuan deserts, two very different ecoregions with disparate plant communities. Dramatic elevation changes result in distinct vegetation zones that can vary from desert scrub to spruce-fir forest in a single range, sometimes within the space of a few miles. Add in the climatic phenomenon of a summer monsoon — a seasonal wind pattern that produces powerful thunderstorms in July and August — and you have all the ingredients for a world-renowned biodiversity hotspot.

Ascending the steep slopes of a Sky Island mountain range, one encounters a series of distinct lifezones, each with its own particular array of plants and animals — from high coniferous forests to the grasslands and chaparral of lower elevations — and a spectacular array of species thrives in the transition zones and microhabitats in between. For example, in the mid-elevation Cave Creek area of the Chiricahua Mountains, research points to the world’s highest diversity and density of nesting birds of prey.

Some species, like the Mount Graham red squirrel, occur only in a single mountain range after evolving in isolation, surrounded by deserts; the red squirrel is just one of about two dozen species endemic to the Pinaleños, the highest of the Sky Island ranges. Various species of talus snail species are likewise limited to a single mountain range, Arizona’s Santa Rita Mountains. Such species are particularly vulnerable to threats like large-scale resource extraction and climate change, the latter of which jeopardizes the Sky Islands’ numerous perennial streams, crucial to many species’ survival. The entire home range of the Mount Graham red squirrel is threatened by a single array of large telescopes, while rare talus snails faces extinction as a result of a single open-pit copper mine proposal.

Many species in the Sky Islands region occur at the northernmost or southernmost extent of their ranges. Endangered jaguars and ocelots, for example, roam into the mountains and canyons of southeastern Arizona and southwestern New Mexico from larger populations to the south. Other subtropical species found in the Sky Islands include the coatimundi, elegant trogon, thick-billed parrot and Mexican garter snake. Conversely, the region harbors the southernmost occurrence of pure spruce-fir forest on the continent.


It’s no coincidence that the Center maintains its headquarters in the Sky Islands; in fact, our founding more than 20 years ago was spurred by efforts to gain federal protection for the Mexican spotted owl, an iconic denizen of the region. Our work to protect this and other Sky Islands species has produced significant — and at times dramatic — land-management changes that have left a living legacy. Over the years, we’ve successfully advocated for listing a number of Sky Island species — including the southwestern willow flycatcher, spikedace, loach minnow and Chiricahua leopard frog —  and for the protection of millions of acres of habitat. In the late 1990s, litigation against the U.S. Forest Service (which manages much of the Sky Islands) led to removal of cows from many streams and other changes in management. Based on newly listed species and other new information, the Center recently reinvigorated this suit and hopes to gain further protections for endangered species. In late 2010, we filed a notice of intent to sue the Forest Service to stop habitat destruction harming the iconic Mount Graham red squirrel.


Other recent work includes scientific petitions to list the Rosemont and Sonoran talus snails, as well as three plants — the Bartram stonecrop, beardless chinch weed and Coleman's coralroot — under the Endangered Species Act. All five species are threatened by plans to build an enormous mine — the controversial mile-wide Rosemont Copper Mine — in the Santa Rita Mountains, where mining activities and waste would destroy at least 4,400 acres of habitat. Besides submitting comments on the mine’s devastating impacts, in 2011 we joined with allies to sue the Forest Service over its preparation of the Rosemont mine “environmental impact statement” without allowing public participation in meetings on key Rosemont issues. In May 2012, in response to legal action brought by opponents including the Center, the Arizona Corporation Co`mmission voted to delay construction of a high-voltage power line needed for Rosemont's construction until the project's proponents could get major environmental permits. In summer 2012, as part of a 2011 landmark legal settlement by the Center to speed protection decisions for 757 species, the Sonoran talus snail, Bartram stonecrop and beardless chinch weed were granted positive “90-day findings” from the U.S. Fish and Wildlife Service, kicking off one-year reviews of the species’ statuess to determine if they qualify for federal protection.

In May 2014 things started to look up for the Santa Ritas and the species that call it home: The U.S. Army Corps of Engineers concluded that that a mitigation plan by the Rosemont Copper Company — required to comply with a Clean Water Act permit — was inadequate to protect regional water supplies, wildlife habitat, natural springs and wetlands. In a letter sent to the company, the Corps explained plans to close the books on more than a year’s worth of work with the company to develop an adequate mitigation plan and pivot toward a final decision on Rosemont’s permit application.

But in May 2017 the U.S. Forest Service published a notice in the Federal Register declaring it would issue a decision on Rosemont in less than a month, in early June of that year — a premature decision that would fly in the face of the law, since other outstanding permitting reviews — including the Clean Water Act permit recommmended in the Army Corps' 2014 letter — haven't been completed.

Banner photo of Santa Rita Mountains by Alan Schmierer/Flickr