Hay-fields are large yellow areas with big yellow rock type structures(hay bales). Helicopter Crash sites and Patient Zero can spawn in a Hay-field. Loot never spawns here, other than the Helicopter Crash loot. Hay-fields are good for picking off targets, as they have numerous amounts of cover, and you can move from one to one, very easily. There is even(surprisingly) a camouflage for Hay-fields, it is the Desert camouflage, which as you may know is one of the rarest camouflages in the game.