That is a camel spider, they became famous on social media when the US invaded Iraq in the middle east where they are more common, and the troops started taking pictures and sending them home. Apparently they are also found in the SW USA, which I didn't know. Good news is they aren't venomous, they just have really nasty jaws that can rip and shred flesh. They're known to "chase" people, but really they're only trying to hide in the shade of people's shadows. If one comes after you, just stop moving and it will stop too, it's just trying to use you as shelter from the sun.
From wikipedia: