The Tumacacori Highlands are an extended area of high country and rolling hills. Two primary named mountains make up most of the highlands - the Atascosa Mountains and the Pajarito Mountains. This area connects to another oak woodland zone in Sonora compoed of the Sierra Cíbuta, Sierra Guacomea, Sierra Las Avispas, and Sierra Esmeralda.
Oak savannah and oak woodland with a heavy Madrean influence dominate almost all of the Tumacacori Highlands. Several species are uncommon or don't exist elsewhere in Arizona including the well-known chiltepin (Capsicum annuum var. glabriusculum).