Triorla interrupta (Robber Fly) ♂.
Size: approx. 25 mm. Photo: 07/19/11, 10 am.

Triorla interrupta. This pretty big robber fly often kills even larger insect prey including grasshoppers and dragonflies. It likes open grassy terrain. This specimen has been identified as a male on the bug guide. 
bug guide (this photo):
Herschel Raney: