What a great picture... have to visit Huaywash soon !
The plants on your picture need a lot of water and are from the Juncacae family. It seems to be either Distichia muscoides or Oxychloe andina.
Yareta (or llareta, Azorella compacta) grows far from water and belongs to a completely different family (Umbelliferae).
more info on : http://www.worldwildlife.org/wildworld/profiles/terrestrial/nt/nt1001_full.html