You are correct that it is extremely hard to find specific rules for that area...actually for any federal lands. In general, most places allow limited amounts of berry picking and mushrooms. But if you are collecting anything else, you will need to check directly with the governing body and even then you might get different answers.
My husband eats acorns and they are not considered a fruit so he can't collect them in state parks, etc.
Here is some general info, but doesn't get specific about BW
Foraging in MN