I'm pretty positive that Mariner Valley isn't supposed to be a sector of Tharsis; it's actually more like another region of Mars completely. Just east of the real-life Tharsis region on Mars is an enormous canyon, called the "Valles Marineris" - Latin for "mariner valleys". It's not really considered part of Tharsis, though it is right next to it. Since the game's Mariner Valley is very likely near the Badlands, due to its similarity and the fact it's full of Marauders, that would place it somewhere close to the southeast of the Tharsis region map - which is pretty much exactly where the "Mariner Valleys" are in relation to the real Tharsis.
So, basically, I don't think Mariner Valley is really part of Tharsis - it's a whole other region.
Also, something else interesting: while the western end of the Valles Marineris canyon system is right next to Tharsis, the far eastern end connects to a region called Chryse Planitia. You can probably guess where I'm going with that. :P Alazar88 20:27, August 21, 2010 (UTC)