Solifugae! (aka "Sun Spiders" - though they're not really a spider). We have them here. One of the ugliest critters you'll run across - right up there with Jerusalem Crickets. Pretty harmless. I hear the bite can be painful, but there are no known poisonous varieties, so it's just a wicked pinch.
I don't know how big the ones in Arizona get, but the ones that made the dirt come alive through night vision in Iraq while camping on overwatch or manning an OP made me wish like hell that I could carry bird shot.
Most of the ones I've seen here are a couple of inches long or smaller - which implies that there are likely some that are twice that big. Night time is a whole 'nother world in the desert, and I miss seeing most of it. ZZZzzzzz....
