Petty thick. Each slab is ~8-12" deep. Make great landings. All harvested on site.
We have a wall holding pretty much the entire area from the foundation of the house. It holds the soil beneath the deck, the landing, and keeps the soil stable over the piers. It is not our normal walling style, but very primitive to match the owner's taste. She is about about 70 and wanted a rustic look... Matches the style that was already used there. It is, however, a stable, working wall and is backfilled with a sand/gravel/rubble mixture we have had great luck with. The base is gravel and crushed native stone. These are before and in progress pics taken before capped.
We have a buttermilk/moss slurry that we pour after sand settles... It looks nice once established.
Here is another that gives you an idea of the slope. It is pretty steep.