Tehuacan-Cuicatlan Valley, part of the Mesoamerican region, is the arid or semi-arid zone with the richest biodiversity in all of North America. Consisting of three components, Zapotitlan-Cuicatlan, San Juan Raya and Purron, it is one of the main centres of diversification for the cacti family, which is critically endangered worldwide. The valley harbours the densest forests of columnar cacti in the world, shaping a unique landscape that also includes agaves, yuccas and oaks. Archaeological remains demonstrate technological developments and the early domestication of crops. The valley presents an exceptional water management system of canals, wells, aqueducts and dams, the oldest in the continent, which has allowed for the emergence of agricultural settlements.