Digging A Really Deep Hole

If the mood strikes you to go out in the woods and dig a really deep hole, just to see how deep of a hole you can dig, remember this:

Don't start the hole on top of a hill. No matter how small the hill is. Dig it next to the hill. Preferably in the valley between two hills.

The lower-lying areas have much deeper layers of easily diggable topsoil. This is a result of naturally occurring processes.

The digging there will be much easier for much longer than it would be on top of the hill. Until you hit those rocks.

Then you'll need the pick-axe.