I have to mention a chapter from "Bacon and Beans from a Gold Pan" - the true story of depression-era miners(no, not this current depression!).
Dot and Jeff Coffey were barely squeaking by, making a dollar or two a day,(1930's money) when Jeff noticed the flat, horizontal stretch of bedrock up-creek from
their camp. Seeing some tiny cracks in this bedrock, he decided to "pop" the rocks. Well, underneath the bedrock chunks, he found a very thin layer
of clay and silt which he scraped off carefully and placed into his gold pan. Long story short, they started making about 10 dollars per day til that
stretch of creek was exhausted.