To the east, the xeric Tehuacan Valley matorral ecoregion occupies the Tehuacan valley to the northwest, the Balsas dry forests ecoregion occupies the upper basin of the Santo Domingo River, which lies in the rain shadow of the Sierra Madre de Oaxaca. The Southern Pacific dry forests ecoregion lies to the south along the Pacific Coast of Mexico, extending into the upper basin of the Tehuantepec River and the Valley of Oaxaca.
This region encompasses the semi-arid Tehuacan Valley matorral ecoregion to the east, which covers the Tehuacan valley in the northwest, alongside the Balsas dry forests ecoregion occupying the upper basin of the Santo Domingo River, situated in the rain shadow of the Sierra Madre de Oaxaca. The Southern Pacific dry forests ecoregion stretches south along the Pacific Coast of Mexico, encompassing the upper basin of the Tehuantepec River and the Valley of Oaxaca.