Hey Russell,
I had beams from an old post and beam barn under tarps on my property for a while. The snakes loved to curl up in the small gaps between the beams and in the mortices (about 2"x6"). We couldn't move a beam without disturbing at least one snake.
I also had a friend who grew potatoes in
straw with
compost. She got lots of potatoes and tons of snakes. So I think they like warm dry places with lots of small spaces where they can curl up. I'm going to try things like:
*A large flat rock propped an inch off the ground on one end and surrounded by logs or brush.
*A loose pile of logs - I'll probably cut some mortices into the logs as I have the technology
*piles of straw near the Japanese beetles favorite
trees
*upside-down half flower pots
There are some great threads on permies about garter snakes. Just Google "permies garter snakes" and at least 4 threads will pop up.