Originally posted by jonnin:

There is an item that tells you where to dig for such things later on.
doing it without is risky. You will find a standard (first one you can make) chest when you dig. Its usually not much deeper than you can stand in and not be underground (below the surface I mean)

Good to know thanks for the info. I just like to have a general idea of what to expect. Even if I only ever dig for treasure once or twice.