The Sierra El Tigre of northeastern Sonora is a rugged Sky Island mountain range. It covers substantial terrain – its basal area spreads out over 600 square miles. Surrounded by the Rio Bavispe valley on three sides, it is somewhat isolated from neighboring high country, except from the south where it is nearly a peninsular extension from the spine of the Sierra Madre Occidental. The Sierra El Tigre is separated from the Sierra Madre by a pass of rugged hills that rise to around 1,200 to 1,600 meters (INEGI, 1998).
Mixed conifer forest grows only at the highest elevations and north facing parts of the Madrean Sky islands, generally over 2150 meters. Species that define mixed conifer are Pseudotsuga menziesii (dug fir), Abies concolor (white fir), and Pinus strobiformis (southwestern white pine).