The Sierra Madre mountain system consists of the Sierra Madre Occidental (to the west), the Sierra Madre Oriental (to the east), and the Sierra Madre del Sur (to the south). These ranges enclose the great central Mexican Plateau, which itself is a part of the system—although the northern portion of the plateau also is considered to be part of the Basin and Range Province in the United States—and is broken by blocks of mountain ranges and large ephemeral drainage basins called bolsones (“pockets”)