Based on a cursory Google searchch 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.

-Also, mushrooms are fungi.

-Thirdly, you don’t want to eat Amanita Muscaria aka fly agaric unless you have thorough knowledge of what your doing. It contains a hepatotoxic compound (hence the deer piss reference in someone else comment) and it’s not to be confused the Psilocybin containing mushrooms AKA magic mushrooms. —The more you know 🌈