Looks like some spalted sycamore I have. Sycamore is a member of the maple family, but I don't know what grows in that area.
I guess once it's spalted it's just called "spalted maple"?+1 Big leaf maple. Maybe red maple if from a colder inland areas of NW.
Doubt it is Alder, as it has grey/tan tones, not the yellow red tones shown in pictures. Alder sapwood and heartwood are same colors and hard to distinguish too.
https://www.wood-database.com/wood-filter/
http://www.hobbithouseinc.com/personal/woodpics/
Cheers!
- CaptainKlutz