Hi rjasonj and welcome to our Forum!
You're correct in posting a new topic for this. If a thread doesn't already exist, we definitely want a new topic created. So thanks!
When you find the location of a dig site, you need to click on the site (it looks like rubble sticking up out of the ground) and click "Excavate." You Sim will start digging at that spot and you'll get messages about what he/she has found, which all go into your Sim's inventory.