On Friday, June 14, 2019 at 9:28:58 PM UTC-5, DerbyDad03 wrote:

And yet we don't see the marks on *all* pressure treated wood. At least I
where I live, even on wooden docks. Maybe it's a west coast thing?

It's probably where you live in some applications, you just might not notice it often. Here in south Louisiana, all the wooden cross members on the older wooden high line poles have those slit marks.

I had salvaged some 4X4 cross members, long ago. I had supposed they were treated, but had no idea the slits were part of the treatment process. Cutting/sawing it, to make a porch swing, produced a foul odor, from the chemical(s) no doubt.

Sonny