My favorite place of all to look into is a north facing slope/holler/ridge where their are large Maple trees and or alot of maples.
My 2nd favorite spot to look is in an area that has alot of vines droping down with maidenhair fern and/or solomon's seal and most of the time the soil will be blacker in color when you find them vines and the fern together,very,very good soil.
I find it where their is Black coash,blood root,golden seal,stone root and even though these dont seem to be as sure as those above I still like to see them often in a mountian especialy if their is not much Maple,or madienhair fern around the area.
But if you ever find a northern side of a mountian with alot of old maples around that has not been found by someone or dug by someone in a good while.Just get ready to thank the good Lord for what you are about to exsperience :o) then post the pictures and I`ll be happy for you to