There are no "Offical Fields" in Utah. Most of the teams and organizations play on land that they obtained permission from the owner to play on. If you want to play with some teams check out Black Thorn Airsoft (BTA) or Just For Fun Airsoft (JFFA). Both welcome walk ons and are pretty cool dudes to play with.
Hic Pro Pugna!!! (“Here For The Fight”)
Tokyo Mauri VSR-10 G-spec (Highly Upped)
TSD M9 GBB
UTG M3 Shotgun