Based on a cursory Google search with the terms "bighorn sheep"+"Psychoactive fungi" it would seem they are referring to rumors of a psychoactive lichen that have not been formally identified.

-secondly, you don't want to eat Amanita Muscaria aka fly agaric mushrooms unless you have thorough knowledge of what you're doing. It contains a hepatotoxic compound (hence the deer piss reference in someone else's comment) -and it should not be confused with the Psilocybin containing mushrooms AKA magic mushrooms. They do different things in the brain—The more you know 🌈 🌟