Wow. I went into this expecting something kind of cracky; instead, you really pulled off something beautiful and unexpected. I love the idea of Severus as "El Curandero" - it seems fitting, given his generally enigmatic nature - and I really enjoyed your OCs - Anna, in particular, but also the idea of Senor Roa (and his jealousy-provoking masculinity!). I liked the legend of El Curandero's scar, and the way that Harry discovered that he was, in fact, 'revived'.
I have to say, you kind of got me a little teary because of the setting: my parents are both from Alpine (and my Dad, in particular, thinks that Big Bend is about the most perfect place on the planet), and although I've only been a handful of times, it's a place that's very near and dear to me - and now it has it's own Snarry. Very well done, indeed. :D