According to The Nature Conservancy, they traverse five ecological communities and contain "the highest diversity of habitats of any mountain range in North America.

"[1] The highest point is Mount Graham (Western Apache: Dził Nchaa Sí'an—"Big Seated Mountain") at 10,720 feet (3,267 m).

[2] The mountains cover 300 square miles (780 km2) and are part of the Coronado National Forest, Safford ranger district.

This is similar to what Charles Darwin discovered with species he collected from different islands in the Galápagos, a discovery that played a major role in his theory of natural selection.

Trees that grow there include: Douglas fir, Engelmann spruce, quaking aspen, Ponderosa pine, silverleaf oaks (south-facing slopes), box elder, and bigtooth maple.

The Mount Graham red squirrel was once considered to be extinct, but was "rediscovered" in the 1970s and as of June 3, 1987, is officially listed as endangered.

The lava-based mountains found throughout Arizona tend to be barren, whereas the Pinaleños (and others) have a large number of trees, including many that pre-date Columbus's arrival in the Americas.

Atop mountain peaks throughout southeastern Arizona and southwestern New Mexico, soldiers manned stations using mirrors, or heliographs, to flash messages across great distances.

"Many of the improvements at campgrounds, as well as hiking trails, roads and other facilities now enjoyed by many visitors to Mount Graham, were built by the CCC personnel.

"[4] One of their projects included the construction of a 99-foot (30 m) steel framed lookout tower on Heliograph Peak to watch for fires in the Pinaleños and nearby mountain ranges including the Galiuros, Dos Cabezas, White Mountains, Gilas, Rincons and Santa Catalinas.

The U.S. Forest Service claims that "prior to about 1870, the Pinaleños maintained healthy, resilient ecosystems that were adapted to naturally occurring fire regimes (primarily frequent, low-intensity wildfires)."

They go on to explain that "After European settlement, the natural ecosystem processes were interrupted by passive (overgrazing) and active fire suppression, and harvest of large-diameter trees.

The result is that today the forests are composed of overly dense, small-diameter trees and snags with excessive amounts of downed wood.

The agency states that "global climate change and drought are helping to poise the Pinaleños for epidemic insect or disease outbreaks and catastrophic, stand-replacing fires.

The flora and fauna have not evolved to tolerate these new conditions or catastrophic events, so there is a need to use silvicultural management and prescribed burning to begin to restore the natural balance in the remaining forests and woodlands.

With unparalleled observational capability, astronomers will be able to view planets in distant solar systems, and detect and measure objects dating back to the beginning of time (14 billion years ago).

Second, some environmentalists worried that construction of the site would adversely affect the endangered population of the Mount Graham Red Squirrel.

[11] Astronomers and other personnel working at the site have faced protests, threats of physical violence, and attempts at sabotage on the mountain.