Two things shape a surround in this town, and neither is the pool. What the creek laid down under the garden decides whether it stays flat, and the afternoon sun decides whether anyone uses it.
Fontana sits on the Lytle Creek alluvial fan, so a back garden is sand, gravel and rounded stone dropped by water. That drains, which is why nobody here fights the swelling clay that lifts decks in other towns, and it is also why a surround can sit on a buried wash channel that was never as tight as the ground either side of it. We dig beside the shell before quoting, and where a seam shows up it is dug out and made up in compacted lifts rather than bridged.
The other half is temperature, and it is the reason people replace decks that are not even cracked. Air in the mid-90s through July and August puts a sealed, dark surround far higher again, and a pool nobody crosses at four in the afternoon is a pool nobody uses. A light broom or a salt face on the same slab reads several shades cooler underfoot, and it is a choice made before the truck comes, not after.