If you dig it up, break it into little pieces and let it dry out completely. Then rehydrate it in plenty of water and it will dissolve. If you let it set a while, you can pour off the water slowly, but the clay slurry will remain higher than rocks and heavy dirt. It takes a while and some practice, but with native pottery, you end up adding a lot of grog, or other crushed rock, sand and old fired pottery shards anyways, so nowadays, I just try to select clay with very little organic matter in it (leaves and twigs) and I don't try to overly process it down. I just add a little more grog and and wedge the clay well and away you go. I'm still learning as I go, so I am not expert at all....but I know as far as what the native peoples had, trying to process the clay perfectly clean would have been a wasted step since you typically add grog anyhow. God made dirt, and dirt don't hurt. This will be good for small cups and bowls like I've done. I am working on some bigger pieces that have plant fibers in them to bind them together... just takes some trial and error really.
