I don't think there's a pot in there. The rocks are shaped to the base. A pot wouldn't fit the base like that. I've seen those that are like that but these are different. I'm trying to make one now. I'll post a photo when I get done.
Those are some of the coolest containers I have ever seen, thank you for sharing that Echinacea!! I'm stunned that she said it takes about an hour to do a smaller one, WOW!!! Must take loads and loads of practice to get that good at it!