The snake river canyon around Twin Falls has always had pigeons. Today there are large feed lots and dairies in the area as well that attract them and they are considered a pest. I think the outfitters are hunting off of these operations.
Here is vintage video of some old pigeon shooters in the Snake river canyon at Twin Falls Idaho. The whole video is great but Look at about the 3:00 minute mark. Not much has changed in this area since then.
https://www.youtube.com/watch?v=jDs3lg5ZoCs
PML