There are no specified fields in the area that I am aware of. I do, however, have a group of people who play in Firth every Monday night at 6. It is a very small town just north of Blackfoot. We have a facebook page that we update regularly with match dates and times. Our organization is called Idaho Airsoft League. Just give us a search. I'm on facebook way more often than I'm on this forum.
Echo1 G36c (stock)
UTG L96 (stock+homemade hop-up)
KJW 1911 kp07 (stock using co2)
Well mp5k (stock)
UTG M3 S tri-shot shotgun
Well mb03 R700 (broken).