Rich pickings

Can anyone enlighten me as to the origin of the phrase "rich pickings"?

My guess is that it refers to the (mainly) women who would during the nepoleonic wars (after a battle had ended) trawl the dead bodies left on battlefields for anything of value.

I associate it with gold mining, but I don't know that that's its origin.

It's the opposite of "slim pickings," meaning not much to choose from. I always associate it with food harvesting (picking fruit off a tree, for example) but I have no evidence to support this.

Well. Now. I've done a little more research, and I can't find support for my harvesting origin ... except as picking through leftovers is harvesting.