Wow if I saw that hole I would have NEVER thought a snake had dug that out!! I would just assume the animal had legs! I like that you are trying different substrates and it shows how smart the snake is.
I went up last week Sunday to a sandridge and saw nothing at 9am, Its really hot lately. At 4 am I was at work outside and thought I was in a oven the pavement was still expelling heat...just unbearable.

