I dug out a French drain. Without measuring I'd say that I dug a 30 foot trench a maximum depth and width of 12 inches. I dug out 4 rocks weighing at least 50 lbs each, and probably much more.
Here's the trench:
Here's the rocks (that's a man sized hand, although probably not a Paul sized hand):
So, if you live in an ancient flood plain, and you want an easy planting, consider a
raised bed. If you need some rocks for a
project, consider getting out the shovel
.