I always used to ignore these things, but visiting the Upper Peninsula and being shown some of the dig sites really gave me more appreciation for them-- in many places people are digging through mine tailings, it's a mixture of broken rock, overburden, and even plants and trees that have overgrown the old piles of waste rock-- its slow, hard digging and with a few very loose guidelines for what areas might have a greater chance of producing something, its like trying to find a needle in a haystack.