In the dry regions of high mountains, communities often live in small oases; relying on rivers fed by snow/glacial melt waters, villagers develop gravity-fed networks, so as to irrigate their surrounding valleys and terraces. Our two case studies, Uspallata (12 km2) in the Mendoza River Valley of the Central Argentinian Andes, and Mustang District (almost 2000 km2) in the Kali Gandaki Valley north of the Nepalese Himalayas, illustrate the functioning of oasis systems and recent changes brought about by the development of roads, related to their position close to international boundaries.