Foundation is dug out (almost!)

Digging the hole in the ground for the Astroshack foundation was delayed last weekend by some hangar painting work - and we just had too many heavy showers passing through that I would have been digging mud.
I did some more work tonight and dug out the foundation area down to the gravel level under the backyard.  The yard was basically a filled in area years ago when the house was built, and I think I'll have some tough digging for the pier ahead.  I hit a lot of rocks about 8 inches down so at least I'll have a solid "bedrock" to construct on and not have it sink into the ground or anything!
The tree will move soon, I just need Traci to move that since she's a skilled gardener and I can only grow weeds.
I'm thinking of doing a cement slab maybe 10 inches thick.  I have to start some drawing soon to figure out the next steps once digging is done.