Damn Red Rot!

Pretty common when timber gets past its prime.
I have also seen it in young stressed Hemlock also. But not very often.

 

Is that similar to blue stain in lumber. I acquired 3000 square foot of Argentina yellow pine for free from a furniture manufacture here in Pennsylvania because it had what they called blue stain and due to workplace regulations their employees could not cut or machine it. I used it as a floor in my camp. It sure is beautiful after I Sanded and applied 6 coats of urethane. Before and after photos.

 

I like the compass on the floor. Helps you when loading NS or EW.