Hiya Bruce, to answer your question, the gophers were released into two enclosed areas which made them easier to collect when the experiment ended.

It's of course possible that other gophers dug around in the same areas after the initial experiment, but if so, they would have likely dug around in the other devastated areas on the volcano too -- except there's no evidence of it. Only the areas where the scientists released the gophers are healed while the other areas remain practically barren.

Thank you for commenting and for your curiosity Bruce! I appreciate you!