The Sierra Madre Occidental run north to south in western Mexico from the center of the country towards the United States border.

The Sierra Madre Occidental is Mexico's largest range, and the ecoregion extends approximately 1,200 kilometers from southern Arizona to northern Jalisco.

[4] The northern Sierra extends from the US-Mexico border through eastern Sonora and western Chihuahua south to the barranca (gorge) of the Urique River, between 27° and 28° N latitude.

[4] The central Sierra extends from the Urique barranca to the valley of the San Pedro Mezquital River, which cuts through the range from north to south between 22°50’ and 23°25’ N latitude.

It has a mean elevation is 2650 m, and includes several peaks above 3200 m.[4] The southern Sierra extends from the San Pedro Mezquital valley into northern Jalisco.

It consists of several north–south trending ranges separated by wide canyons where lowland tropical and interior arid vegetation converge.

The ecoregion also covers the western end of the Trans-Mexican Volcanic Belt in Nayarit, including the Sierra de San Juan.

Endemic species include the tufted jay (Cyanocorax dickeyi), green-striped brushfinch (Arremon virenticeps), and thick-billed parrot (Rhynchopsitta pachyrhyncha) which is now endangered from trapping for collections.

The eared quetzal (Euptilptis neoxenus) is a near-endemic, ranging from the sky islands of southern Arizona through the Sierra Madre Occidental to the western Trans-Mexican Volcanic Belt pine–oak forests.

[2] Mammals include the Coues deer (Odocoileus virginianus couesi), American black bear (Ursus americanus), cougar (Puma concolor), and jaguar (Panthera onca).

The increase of global warming is expected to have some devastating effects on the pine trees located in the Sierra Madre Occidental.