The region contains sky island mountain ranges, called the Madrean Sky Islands, some separated from the Sierra Madre Occidental proper, and occurring in the northeastern Sonoran Desert, and extreme west-northwestern Chihuahuan Desert.

Sierra La Esmeralda anchors the southern portion of the Tumacacori Highlands.

The Tumacacori Highlands is a series of connected mountain ranges in western Santa Cruz County, Arizona.

The Highlands are northwest of Nogales and are bordered on the east by the Santa Cruz River Valley, that is traversed north–south by I-19.

The sequence of the north-to-south Tumacacori Highlands is as follows: North-to-south: A Santa Cruz county-border "bootheel" extends southwest; the bootheel contains Cobre Ridge, and it is connected northwest to a small range, the San Luis Mountains which are in the southeast of the Altar Valley, and borders the Buenos Aires National Wildlife Refuge.