This is kind of an interesting change of pace, in that the story is really just about a bunch of gauchos sitting around passing the mate around and chewing the fat. One of the gauchos happens to be a great storyteller, so the other gauchos convince him to tell them some stories. (The gaucho as storyteller element comes up in Don Segundo Sombra, too.)
There's an interesting progression to the three stories he tells. The first is a pretty typical folktale about the fox and the jaguar, with the fox and the jaguar being relatives and friends until the fox cheats the jaguar. The second story is something of a ghost story, introducing a human element and some local color. The final story completes the process by being a pretty horrific story of a gaucho and his dog.
There's always something a little artificial about stories within stories, but I tend to find them quite a thrill when they're done well. I wouldn't place this at the top of the scale, but I thought it was quite well done.