[1] It is sandwiched between the larger Tumacacori Mountains to the north, and a small east–west border range to the south, the Pajarito Mountains; the Pajaritos are on the U.S.–Mexico border and abut the Sierra La Esmeralda range in northern Sonora.

Pena Blanca Lake on Ruby Road, arising from the lowest elevations of Calabasas Canyon–(tributary to the Santa Cruz River) are part of the Atascosa's southern border.

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

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