The Rockies come into this series as losers in nine of their last ten games.
Cook had a nice start against Cincy on July 15th, but received the ND. He went seven innings and allowed one run. Brian Fuentes blew the save in that game. This will be Cook's fourth start against the D'Backs and he has a 1-1 record.
Vargas took the loss to the Brewers on July 16th after allowing six runs in three and two-thirds inning. This is his first start this season against the Rockies.
As always, pay a visit to SBNation's D'Backs site AZ Snakepit.