Called my local supplier about some stone material ... asked for #57 but they do not carry anything specifically called that. They do carry #8 (described as 1/2" - 1 1/4" crushed limestone) and #5 (described as 3/4" - 1 1/4" crushed limestone).
Trying to get a feel of how much stone would be needed to backfill a 20x40 rectangle pool. Assuming a 30" overdig and filled from on top of the concrete footer to the base of the deck pour.
Roughly $19 per ton delivered.