Got confused about "Oceanic sound", and started typing in things like pwooosssshhh and other such watery sounds. My brain clicked in the end, I'm happy to say...
Sulps: It's called "Las Pampas", which is plural. The locals may call it "Pampa" (though I've never heard one say it), just like locals may say "The Village" instead of "Greenwich Village", but that doesn't change the proper name of the place.
Sulps is right. I'm argentinian, we call it Pampa all the time, or, if we want to be more accurate, "región pampeana" (pampean region). This would be the "proper name". In any case, it's a small semantic debate, but certainly not a bastardization.
Fun fact: when Pompeii was rediscovered in 1599, the team accidentally dug into what they thought was the house of a man named Pompey. The city of Pompeii had been so far removed from public memory that nobody understood the inscription on a wall that said, "decurio Pompeii." The moral of this story is that accepting "Pompey" as an alternate spelling would be to repeat the mistakes of history.
instead of Pompeii? - If you're going to bastardize, go all the way!