I would actually put Vegas as one of the most sustainable cities in the US out of necessity. Vegas's per capita water use is about 1/4 of the US average including all of those crazy fountains on the strip. They don't irrigate anything compared to places like Phoenix and almost all municipal water hookups use reclaimed water unlike most other cities where people have an aversion to drinking filtered piss. Vegas also gets almost all of its energy from renewable sources (hydro and a tiny amount of solar) compared to the US as a whole which is only about 10%. Colorado by comparison gets about 60% of it's electricity from coal.