I ran both pics on my Picturethis app that identifies trees and plants.
One pic said Japanese cedar and the other with the worm holes said giant sequoia.
I'm sure neither is correct.
Well, quite the diversity of opinions here! Thanks, all. My sister told me that the realtor who brokered the sale of the house between her and the previous owner said the latter identified the wood as… (drum roll)
Wormy chestnut
If that’s true, then the wood is pretty valuable as the source, American chestnut trees killed by the chestnut blight of the early 1900s, was pretty much used up by the middle of the century. My sister’s place was built circa 1950, but I’m not convinced that’s what this wood is, though I’ve never seen wormy chestnut before. So I’m taking a sample from an off-cut back to my shop to try planing and cutting it, and see what further clues I can turn up.