In autumn, they eat a large amount of acorns. Acorns are highly nutritious. Turkeys love them, and so do wild hogs, deer and bear. Domesticated fowl love acorns, too, and periodically a turkey will escape the confines of its cage and join the wild birds for a meal under the oaks. It sounds harmless, but it's not.
Domestic birds carry diseases that can be fatal to wild toms and hens.
If they come to a barnyard where there is food, they will join the other birds. And that works the other way around. It's impossible to say that all the wild turkeys in Humboldt County came from wild stock. I have to believe that a few tame birds got away. In the early 1900s, Humboldt County was a prime location for turkey farms.