Having lived in Phoenix for some 12 years now, we desparately need a theme park that is better than Castles N' Coasters (glorified carnival).  Yes it is hotter n' hell here in the summer, however if you located the park roughly a hour and half north of the Phoenix metro area, say near Prescott, AZ, the summer temperatures are drastically cooler.  That area of AZ is usually 10-15 degrees cooler in the summer time, which, considering we don't have much humidity would make for a reasonably comfortable day.  Also, you would be able to pull from the Phoenix area and Flagstaff as well as Vegas population.