<P> Western Region is one of the least known areas of Mesoamerica . It is an extensive region that comprises the slopes of the Sierra Madre Occidental, a part of the Sierra Madre del Sur y and the middle and lower basin of the Lerma River . The foothills of the mountain were covered by forests of pine and oak, but forestry in the area has reduced its size . The land is suited to cultivation due to its fertility and abundant water resources, especially in the coastal plain of Sinaloa, the Bajío, and the Tarascan Plateau . The climate varies from cold in the mountains, in the east of Michoacán, to tropical along the coast of Nayarit . </P> <P> This region was inhabited by Uto - Aztecan - speaking peoples, such as the Cora, the Huichol, and the Tepehuano . The incorporation of these peoples into the sphere of Mesoamerican civilization was very gradual, and it is presumed that the first ceramics developed in this region were linked to traditions of the Andean people of Ecuador and Perú . The changes that clearly affected the rest of the region are less observable in the West, and for that reason, the cultural traditions of the Preclassic period, such as those of the Colima, Jalisco and Nayarit, or those of the Tumbas de Tiro survived well into the Classic period (150 - 750 CE). The best known of the western societies is the Purépecha, which rivaled the power of the Mexica during the 15th century CE . </P> <P> The North of Mesoamerica formed part of the cultural super area only during the Classic era (150 - 750 CE), during which Teotihuacan's apogee, and population growth, favored migration towards the north and commerce with distant Oasisamerica . The region is flat, compressed between the mountain ranges of the Sierra Madre Occidental and the Sierra Madre Oriental . The climate is dry, if not desert - like, with scarce vegetation, for which reason agriculture was only possible through the canalization of surface water currents (especially the Pánuco River and the Lerma tributaries) and the storage of rain water . The excessive dependence on good weather led the people of the North to abandon the region in the middle of the 8th century after enduring a prolonged drought and invasions of Aridoamerican people . </P> <P> The centers of population in the North were dependent on the network of commerce that was established between Teotihuacan and the Oasis America societies . Sites such as La Quemada in Zacatecas, and La Ferrería in Durango served as forts to guard the commercial routes . When agriculture and the social system collapsed in the North, the occupants of the region migrated towards the West, the Gulf, and the Center of Mexico . </P>

Mesoamerica contains all of the following geographic features except