 The delineations between the Monte Desert, the Atacama Desert, and the Patagonian Desert are not exact and the desert seems to be more-or-less continuous with the other two nearby deserts.The geography of the land is very similar to that of the interior Patagonian Desert, with volcanic sediments, piedmont plains, large mountain blocks and many usually dry salt lakes.The major river is the Río Colorado and its tributary the Río Desaguadero, which meet in the south of the region and provide its principal source of irrigation water for wine crops.