Chiricahua Mountains in the context of Dos Cabezas Mountains

Sky islands are isolated mountains surrounded by radically different lowland environments. The term originally referred to those found on the Mexican Plateau and has extended to similarly isolated high-elevation forests. The isolation has significant implications for these natural habitats. Endemism, altitudinal migration, and relict populations are some of the natural phenomena to be found on sky islands.

The complex dynamics of species richness on sky islands draws attention from the discipline of biogeography, and likewise the biodiversity is of concern to conservation biology. One of the key elements of a sky island is separation by physical distance from the other mountain ranges, resulting in a habitat island, such as a forest surrounded by desert.

The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins. The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch.

The numerous ranges within the province in the United States are collectively referred to as the "Great Basin Ranges", although many are not actually in the Great Basin. Major ranges include the Ruby Mountains, the Snake Range, the Panamint Range, the White Mountains, the Toiyabe Range, the Sandia Mountains, and the Chiricahua Mountains. The highest point fully within the province is White Mountain Peak in California, while the lowest point is the Badwater Basin in Death Valley at −282 feet (−86 m). The province's climate is arid, with numerous ecoregions. Most North American deserts are located within it.