They are a version of maple I believe. The picture here is when we got them fresh (and soaking wet) from the family farm. This amazing little family farm in Maine was having a sale on their lumbered pieces it was awesome. I forget the kind of maple he said it was but I’m pretty sure it was a maple.
Here’s some other pics from the place, I could’ve bought so many lol
I couldn't tell you exactly which type of maple tree, but in these pictures it definitely looks spalted.